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Crane Electronic Ignition

It is a major component of the Electronic Ignitions.

We have the official crane installation manual available here. The John Hassel Installation tips of 15th of April 2002 form most of the contents of this section and the section on the [[IgnitionSystem | Ignition System]. John's original document is only available to Full Members in the Restricted section, and linked below here.

Crane XR-700 Installation and Tips

By John Hassell, Texas, 15 April 2002


This document describes installation and testing of the Crane XR-700 Optically-triggered Ignition System into a 1969 Mercedes Benz 280SL. It is not meant to replace the installation instructions that come with the ignition system, but rather to supplement those instructions with first-hand experience.

Proper installation, testing and adjustment of this device require succinct knowledge of ignition systems as well as standard ignition test equipment. Only qualified personnel should attempt it.

Function of the Crane Ignition System

Points are mechanical, subject to bounce and vibration and must be actuated - mechanically - by the camshaft in the distributor. Whereas the wear on the point contacts has been reduced, the fiber pawl, which rides between the points and the distributor camshaft, can still wear out or break. A method needs to be found whereby the failure-prone mechanical points can be replaced with some other type of trigger for the ignition. The Crane XR-700 Optically-Triggered Ignition System accomplishes this by using a solid-state trigger, which replaces the points.

Shutter and Trigger Assembly

Note that this is not a magnetic or Hall effect trigger; it uses a light-emitting diode (LED) and a photoreceptor interrupted by a shutter. The shutter fits onto the distributor shaft and has six small slots (for a six-cylinder engine). The figure shows the shutter and LED sensor/trigger assembly, both of which are mounted inside the distributor.

When one of the slots appears between the LED and receptor (as shown in the figure), a pulse is generated and sent to the control module, which in turn, sends a pulse to the ignition coil, triggering the spark. Since the LED and shutter assemblies endure virtually no wear, the ignition system is no longer prone to point failure. The XR-700, when properly installed, will reliably trigger the coil at engine RPM beyond red line. An optically triggered system also eliminates point bounce and misfiring at high RPM and provides a consistently reliable spark. Since there is no mechanical friction point between the distributor camshaft and the trigger module, the system should last indefinitely; theoretically at least.

As with the Mercedes Benz transistorized ignition, the Crane system uses a high power transistor to handle the current through the ignition coil. The optical trigger in the distributor is used to control the transistor.

Shutter closed

This diagram shows the trigger module in the distributor with the shutter closed, that is to say, the optical path between the LED and the photoreceptor is blocked. In this mode, the output to the ignition module is 0 volts.

Shutter open

This shows the trigger module with the shutter open. There is now a clear optical path between the LED and the photoreceptor and the receptor turns ON. At this point, the output to the ignition module is 12 Volts.

As the shutter rotates on the distributor shaft, the action continues for each cylinder causing the ignition module to initiate the spark through the ignition coil.

The points have now been eliminated completely and replaced by a solid-state trigger module that receives virtually no mechanical wear. The "Achilles Heel" of the system is gone; engine reliability is significantly increased.


  1. Points are the weakest link in a conventional, Kettering ignition system.
  2. Transistorized ignition systems improve point life by reducing current
  3. Optically triggered systems eliminate points and increase reliability
  4. Transistorized and optically triggered systems do not necessarily improve engine performance or create a hotter spark
  5. Optically triggered systems provide a consistent spark at all RPM

Installation Instructions and Tips

The procedures described herein are intended to supplement the installation instructions that accompany the Crane system. The tips and advice offered are based on actual installation of this system into a 1969 280SL. Generally, the process follows the Crane instructions.

Crane XR-700 in Author's 280SL - Above Sub-Frame Mount

Installation Options

The tools and materials required for installation depend upon where the control module is mounted in the engine compartment. A clear, flat space approximately 3-1/2" square is needed for the module. DO NOT mount the control module to the engine. Possible locations are the firewall, fender, etc. Any location will suffice as long as air can flow over the module to cool the internal power transistor. If your 280SL uses the Mercedes Benz transistorized ignition module, you can remove the module and replace it with the Crane module.

The Mercedes Benz module is mounted under the battery rack and can be accessed only from under the vehicle, or with the battery and battery shelf removed.

The author elected to mount the Crane module above the left-front sub-frame mount on the driver's side fender well, as shown in the photograph.

Equipment Tools and Materials Required

If you elect to mount the control module in a manner different from the author's, please refer to tables below for components, test equipment, tools, hardware and materials. If you wish to mount the module in the same manner as the author, please refer to the additional items required as listed in the last table.

Components Required

  • 1 x Crane XR-700 Ignition System
  • 1 x Ballast resistor, Bosch 0227 901 013

Test Equipment and Tools Required

  • Multimeter, DC, analog or digital
  • Timing light
  • External electronic tachometer
  • 5mm hex key, 1/4" drive, with integral universal joint
  • 1/4" drive T-handle
  • Screwdriver, flat-tip, stubby
  • Screwdriver, #2 Phillips, stubby
  • Nut driver (or open/box end wrench), 8mm (coil terminals)
  • Nut driver (or box-end wrench), 7mm (ballast resistor terminals)
  • Electric drill, 1/4" chuck minimum
  • Drill bit, 9/64"
  • Terminal crimping tool/bolt cutter, standard

Hardware and Materials Required

  • 1 x Rubber grommet, 3/8" ID, 1/2" OD
  • Tube of RTV self-vulcanizing rubber, any color
  • 6 x Round terminal lug, crimp, #10 stud, AWG16(blue)
  • 4 x Screw, sheet metal, #8 x 3/4", galvanized

Optional Hardware, Tools and Materials

  • 4 x Threaded hex spacer, 2" long, 6-32 thread
  • 1 x Aluminum plate, 0.050" thick, 4" x 4"
  • 8 x Screw, 6-32x1"
  • 4 x Hex nut, 6-32x5/16"
  • 4 x Hex nut, 6-32x1/4"
  • 16 x Lock washer, internal tooth, #6
  • 1 x Tap, 6-32
  • 1 x Tap handle/driver
  • 1 x Drill bit, 7/64"
  • 3 x Waldom/Molex 0.093" socket pins
  • 1 x Pin removal tool (included with Crane system materials)
  • 1 x Waldom/Molex crimping tool, HT1919

System Components

The following components, as supplied in the Crane kit, will be required for installation of the system in a 280SL

  1. Ignition Module
  2. 6-window shutter with metal clips
  3. Optical Trigger Module
  4. Mounting Arm
  5. Mounting Foot
  6. 4-40 x 3/16 machine screw


Line drawn on distributor housing

  1. Locate cylinder number 1 spark plug port on the distributor cap. Trace the spark plug wire from cylinder 1 to the distributor cap. Mark the cap for cylinder 1.
  2. Draw a clear, easily seen vertical line on the base of the distributor that intersects the exact middle of the number 1 spark plug wire port on the distributor cap. Refer to the diagram.

The line must be exactly in the center. If you place the line correctly, it will save you a lot of grief later.

  1. Remove the distributor cap.
  2. Crank the engine ("bump" the starter) until the rotor is lined up with the line that you just drew on the distributor. See the diagram

Alignment of Rotor With Drawn Line

  1. Turn off the ignition and remove the key from the ignition.
  2. Disconnect the vacuum line from the vacuum diaphragm.
  3. Disconnect the wire from the distributor to the coil or the wire from the distributor to the transistorized ignition module. NOTE: The ignition module is located under the battery tray. There is a small, 2-terminal strip to which the point cable attaches. Remove the two screws and the cable. Refer to the diagram.

Point Cable Connection for MB Transistorized Ignition

  1. Using the 5mm Hex key/universal joint and the Vi" drive T-handle, loosen the holding screw at the base of the distributor and remove the distributor. CAUTION: Do not crank the vehicle while the distributor is removed!
  2. Remove the rotor and points.

Do not drop the screw into the distributor. Save the screw from the points; it will be used later.

  1. Refer to Page 4 of the Crane installation booklet, Figure 8, and attach the optical trigger to the mounting arm, using the 4-40 x 3/16 screw supplied. CAUTION: Do not over tighten this screw. It is threading itself into the plastic housing of the optical trigger and can easily strip the hole in the housing. The screw should be snug enough to hold the optical trigger, but not too tight.
  2. Attach the mounting foot to the distributor plate using the screw removed from the points, as shown in Figure 8 of the Crane booklet. Make the screw snug, but do not tighten yet. Note: Due to the small space inside the distributor, the optical trigger and shutter will have to be installed together. You cannot install the shutter if the optical trigger is already in place.
  3. Install the shutter and optical trigger in the distributor. Carefully place the shutter on the distributor camshaft, then install the rotor and use it to push down the shutter to the proper position. Fasten the mounting arm to the mounting foot with the 6-32 x Vi" screw supplied. Make the screw snug, but do not tighten.
  4. Using a screwdriver, move the breaker plate (plate to which the optical trigger is attached) to see if it moves freely. It will be hard to move, but neither the mounting arm or mounting foot of the optical trigger should touch the side of the distributor; the plate MUST move freely or the vacuum advance and retard will not function properly.
  5. If the optical trigger assembly touches the side of the distributor, it will be necessary to file the mounting arm and foot until enough clearance is achieved.
  6. Install a rubber grommet in the hole through which the point wire used to pass.
  7. Route the three wires from the optical trigger through the grommet. Ensure that there is enough slack in the wires to allow the breaker plate to move freely.
  8. Place a small bead of RTV self-vulcanizing rubber in the grommet to seal the hole from external dust and debris.
  9. Set the distributor aside and wait about 1 hour for the RTV to cure.
  10. Install the ignition module in a suitable location. Use four, #8 sheet metal screws to secure the module. Tighten the screws securely and make sure that the module is lying flat on the mounting surface. Do not tighten the screws if the module is not flat or you will bend and deform the module enclosure, possibly causing internal damage. Note: If you can find a suitable location that affords sufficient airflow for the ignition module, then use it If you want to install the ignition module in the same manner as the author, refer to Section 3.0 for additional instructions, before proceeding.
  11. Locate the ballast resistor that is installed in the vehicle. If you do not have the Mercedes Benz transistorized ignition system in your car, there will be one ballast resistor mounted on the driver's side fender. The resistance of this resistor is 0.6 Ohms. If there is only one resistor on the fender, do not remove it. If you have the Mercedes Benz transistorized ignition installed in your vehicle, there will be two ballast resistors; one will have a resistance of 0.6 Ohms and the other 0.4 Ohms. Remove the 0.4 Ohm resistor but do not remove the 0.6 Ohm resistor. Leave all removed wires and/or terminals open.
  12. By now, the RTV should be cured in the distributor. In the following steps, you will align the optical trigger, place the housing on the wire terminals and adjust the phasing of the optical trigger.
  13. Remove the ignition module from the car.
  14. Find the white, Teflon connector housing supplied with the Crane kit.
  15. Referring to the diagram below, insert the pins on the wires from the optical trigger in the distributor, into the connector housing. Make sure that the wire colors match, black-to-black, white-to-white and gray-to-gray, when the connectors from the distributor and ignition module are mated. Push the pins into the housing until they "click."

Pin Connections for Molex Connectors

  1. Connect the distributor and ignition module to a 12-volt battery or external 12-volt power supply, as shown in the diagram below.

Set-up for optical trigger alignment

  1. Rotate the distributor shaft and ensure that the shutter moves freely in the slot of the optical trigger. There should be no binding or scraping. If there is, you must file the brackets or readjust the optical trigger position. Once the shutter moves freely, you can begin the alignment of the optical trigger's position.
  2. Find the red LED on the ignition module housing. The LED may or may not be illuminated.
  3. Slowly - very slowly - rotate the distributor shaft while observing the LED on the module. Set the distributor rotor to align with the drawn line on the distributor housing.
  4. Adjust the mounting arm and optical trigger until the LED illuminates when the rotor is centered - exactly - on the drawn line, as shown in the diagram above.
  5. Repeat this process several times and ensure that the LED illuminates when the rotor is exactly centered on the drawn line. Tighten the screw on the mounting arm and the screw holding the mounting foot.
  6. Repeat step 29 and make sure that the LED still illuminates when the rotor is exactly centered on the drawn line.
  7. Disconnect all equipment and unplug the connection between the distributor and ignition module.
  8. Reinstall the distributor in the vehicle and snug-up the 5mm holding bolt.

Firing Order Distributor Top View
  1. Install the distributor cap and ensure that all spark plug wires are in the proper ports. The firing order is 1-5-3-6-2-4 and the distributor shaft rotates in a clockwise direction, as viewed from above; refer to the diagram.
  2. You must now determine which wires carry the proper voltages to operate the ignition system. Earlier, you identified the ballast resistors on the interior fender wall. If your vehicle does not have the Mercedes Benz transistorized ignition system installed, refer to the first diagram. If your vehicle does have the Mercedes Benz transistorized ignition system installed, refer to the second diagram.

Wiring without MB Transistorised Ignition

Wiring with MB Transistorised Ignition

  1. If your vehicle has the Mercedes Benz transistorized ignition, remove the 0.4 Ohm ballast resistor and disconnect all wires from it. Also, disconnect all wires from the 0.6 Ohm ballast resistor.
  2. Remove - or tape and secure - the Red/Black and Black wires from the ignition module, if applicable.
  3. Connect the Crane ignition module to the vehicle's coil and electrical system as shown in in the diagram below. Observe wire colors. Cut wires to proper length.

Crane Wiring - 280SL

If your vehicle has an emission control system, there may be a Green/Black wire connected to the negative (terminal 1) of the ignition coil. Leave this wire in place after the installation has been completed. It is connected to the speed relay that is part of the emission control system.

  1. If you wish to shorten the wires to the distributor, you will have to remove the Teflon connector housing on either the cable from the ignition module or the cable from the distributor. Proceed as follows:
    1. Locate the pin removal tool supplied with the Crane kit; it looks like a small brass tube about 2-1/2" long.
    2. Place the hollow tool over the pin you wish to remove and push firmly; the pin will come out of the shell. Repeat for the remaining two pins.
    3. Cut the cable to the length desired. Leave enough length to allow the connectors to be unmated if maintenance is required.
    4. Strip about Vi" of insulation from the end of all three wires.
    5. Acquire the proper pins - male or female - from a Waldom/Molex distributor; Radio Shack usually handles the pins. You will need 0.093" diameter pins.
    6. Using a Waldom/Molex crimping tool, Model HT1919 or equivalent, crimp the terminals onto the wires. Note that two crimps will be required for each pin. The first crimp secures the wire electrically and the second secures the wire physically.
    7. Insert the pins into the connector shell. Ensure that the colors match - side-to-side - when the connectors are mated.
    8. Dress and secure the cable to the existing harness with tie-wraps.
  2. Retain the 0.4 ohm ballast resistor; it may be needed later.
  3. Unless already accomplished, remove the Mercedes Benz transistorized ignition module from beneath the battery shelf, if applicable.
  4. Connect a timing light to the battery and spark plug wire for cylinder #1.
  5. Connect an electronic tachometer to the negative (terminal 1) of the ignition coil.
  6. Start the engine and set the timing to the specifications for your vehicle and gasoline octane used.
  7. Connect a voltmeter between any ground point and the positive (terminal 15) of the ignition coil.
  8. Run the engine at a constant 1,500 RPM and note the reading on the voltmeter. It should read between 10.2 and 11.3 volts. If the voltage is too low, replace the ballast resistor with a 0.4 Ohm unit and retest. If the voltage is too high, install a 0.7 or 0.8 Ohm resistor and retest. Resistors can be obtained from any Bosch dealer.
  9. Road test the vehicle at engine RPM at or near red line. The vehicle should exhibit smooth acceleration with no misfiring.
  10. Route or dress all wires and secure to the existing wiring harness with tie-wraps. Use of electrical tape is not recommended. Tape tends to melt and lose its adhesion under high temperatures.
  11. The installation is now complete. If you encounter any problems, follow the troubleshooting procedures on page 19 of the Crane booklet.

Crane Ignition

Pete Lesler says: I have a Crane ignition replacement kit (formerly known as Allison). It replaces the points with optical sensor and an amplifier. I use the transistorized coil because it is slightly hotter than the older black coil. This system has run for four years without any problems whatsoever. There is another company, Pertronix, which also makes a replacement. It actually looks neater than the Crane installation.

The Crane point conversion kit part #'s are XR-700 unit, -0231 kit. It comes with different shutters for various models. Fairly easy to install and comes with a wire diagram. They run flawlessly. The original ballast resistor is used if you are running the original coil. On the transistor 280 SL's, I have found the .6 ohm resistor is correct, however the switch gear should be unhooked along with the other resistor. I have also tried the Pertronics hall effect unit, but found it weak at crank speed and idle.

Will adds: I too have tried the Pertronix and found it useless. It was for a 190 SL test engine I use to test carb rebuilds. Returned the Pertronix setup for a refund.

I installed the Allison/Crane ignition system on my 190 SL, 250 SL, and 250 SE/C many years ago and am very happy with them. Despite Bosch's recommendation, I have bypassed the ballast resistors on my 250-ies (the 190 SL has none) to get greater secondary voltage out of the existing coil. I had one coil go bad during that time.

Arthur Dalton: I have done several and like the Crane XR-700 part #-0231. It is optical and they run flawless. Comes with switchgear and works fine w/stock Bosch coil. The Pertronics Hall Effect pick-up is easier to install, but does not have as nice a spark [specially at starting]. The advantage is you can't see it has been modified as it is hidden in under the distributor cap. Both are a good improvement over mechanical switching.

On the Crane Cams unit. Amazing results! Installation is easy. You remove the points, and install an optical pickup in their place. A wire connects the pickup to a small electronic control unit, and another wire connects the control unit to the coil. Lastly you adjust the timing. That's it. I paid under $100. Best part is that the car looks completely original. I installed the control unit under the battery tray where it can not be seen.

Absolutely convert to electronic, use the Crane XR-700 Series, model 0231. Stay with the stock coil, it is fine. I have done several and it is a great improvement over mechanical switching points.

Here are some options:

  1. Install the Bosch electronic switching unit that was available on the 113 from late 1969 onwards. The switching unit mounts (usually) beneath the battery shelf and requires a mounting bracket to support it. The system uses the points in the distributor to trigger the spark. There are two versions of this unit: one (the early version) reduces point current from about 5 amps to about 1.5 amps, which significantly increases the life of the points. The later version reduces point current to about 0.4 Amps, which adds even more life to the points. The switching unit was used on sedans as well, so you can probably find one at a local junk yard or parts shop. I believe that they're still available from MB or Bosch, if you check with local dealers, but they're a bit pricey.
  2. You can install a breakerless electronic system such as the Crane XR700 or the Pertronix. Both of these systems eliminate the points and also eliminate the need for dwell adjustments. The Pertronix is simpler and much easier to install than the Crane - the Pertronix unit fits entirely inside the distributor, whereas the Crane has a trigger unit in the distributor and a control unit external to the distributor. Depending on the distributor that you have in your car, it can be a bit of a job to get the Crane trigger unit installed and properly adjusted. For simplicity, go with the Pertronix.
  3. You can also install a multi-spark, capacitive discharge system such as the MSD-6 or something similar. Unless you're going to race the car, however, I believe that such systems are overkill for a 113. Personally, I have the Crane XR700 in my 1969 280SL and I'm very happy with it. No problems whatsoever (except for a loose wire that was my fault), and I don't have to worry about points.

My 300SEL 6.3 has a Crane ignition and it performs flawlessly and you hardly see it.

I just installed a Crane XR700 system in my 1969 280SL. The system works extremely well all the way to red line, but it was a bear to install. I mounted the control unit on a small plate that I installed over the left front shock absorber mount. I didn't want to use the mounting location for the original electronic module since it is installed under the battery shelf and is not easy to access. The wiring was simple and straightforward. Installing the sensor in the distributor, however, was frustrating and time-consuming. Here are the problems you might encounter.

  • The mounting brackets for the sensor array may have to be filed down to a smaller size to ensure that they don't scrape the distributor housing and interfere with the vacuum advance/retard plate. The plate must move freely.
  • If your car has the MB electronic ignition, you'll need a small 1/4" (ID) rubber grommet for the hole that the sensor wire go through in the distributor housing.
  • Make sure that you leave enough of the sensor cable assembly inside the distributor housing to allow the vacuum advance/retard plate to move freely.
  • Once everything is installed, place a bead of self-vulcanizing rubber (RTV) in the rubber grommet as a water seal.
  • The 3-pin Molex connector furnished with the kit (connects the sensor array to the control unit) is NOT waterproof. I used a rubber-encased automotive connector and discarded the Molex.
  • The control unit will require an external ballast resistor unless your coil has an internal one. My coil was standard (no ballast) so I used a 1.6 Ohm ceramic ballast resistor in place of the old one. Here's how to determine if the ballast resistor in your car is OK to use with the Crane system.
    1. Install the Crane system and adjust timing to spec.
    2. With the engine running at about 1,500 RPM, measure the voltage from the coil + terminal to ground. It should be about 1.5 - 2 volts LESS than the battery voltage. If the voltage is too high, you need more resistance; if the voltage is too low you'll need less resistance. Rule of thumb (as noted in the Crane instructions): If the control module seems hot to the touch after 15 minutes or so, you'll need to increase the ballast resistance.
  • The ballast resistor will become extremely hot. If the resistor is new, it may actually smoke until the coating burns off. Believe it or not, this is normal.
  • Phasing. This is the most important adjustment. The spark MUST occur when the distributor rotor is centered exactly on a spark plug wire port. The instructions that come with the Crane system explain how to do this; read them carefully and comply. Basically, if the engine idles smoothly and will run up to high RPMs without missing, the phasing is OK.
  • Remember: Set timing to factory spec for your car and the grade of gasoline that you use. Also, remember that there is no dwell adjustment with the electronic sensor.

The system works very well, but you may run into some problems installing the sensor in the distributor. If you're good with this kind of stuff, set aside a few hours to do the job. If you're not so good; set aside a half-day or so to get it right.

Not familiar with the Pertronix but have had the Crane in my 280SL for 5 years now. Perfect in every way, never a problem.

Crane Distributor Parts

Crane Control Module mounted under the battery tray

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