Author Topic: Puzzling electrical problem  (Read 8754 times)

waltklatt

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Puzzling electrical problem
« on: February 04, 2010, 14:30:26 »
I'm using the ohm meter and checking everything for continuity to trace the electrical no start problem.
1970 280SL with the dreaded transitsorized ignition. 
The ohm meter is moving to zero when I touch the distributor body to the core green wire.  I see two wires in the same green wire, one is the core wire and the other is the sheilded wire the surrounds the core.
Please tell me if this is right?
Sounds like I have a short in the system somewhere.
I just took out the instruments to replace the ignition switch, also replaced the coil, condenser, point, cap and rotor, plug wires and ends, as well as both series resistors.  This thing is driving me up the wall!
Am ready to take a sledge hammer to the car.
Thanks,
Walter
1967 220SL-diesel-no problems
1970 280SL-loads of problems causing a no start.

Naj ✝︎

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Re: Puzzling electrical problem
« Reply #1 on: February 04, 2010, 14:46:08 »
Hi, Walter,

Try using the test procedure in the manual for transistorised ign system to find out whats wrong:

http://www.sl113.org/wiki/Electrical/TransistorIgnition

naj
68 280SL

mbzse

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Re: Puzzling electrical problem
« Reply #2 on: February 04, 2010, 16:42:05 »
hrrm, if it gets to you that bad, perhaps you should consider a 123-ignition distributor unit.
This would be a way around the fiddling with those 40-year old electronics...
Just a suggestion  :)
/Hans in Sweden

.../...This thing is driving me up the wall!
Am ready to take a sledge hammer to the car.
Walter
1967 220SL-diesel-no problems
1970 280SL-loads of problems causing a no start.
« Last Edit: February 04, 2010, 16:44:22 by mbzse »
/Hans S

hands_aus

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Re: Puzzling electrical problem
« Reply #3 on: February 06, 2010, 11:43:09 »
Walter is the small bolt that goes through the distributor body and which the capacitor/condenser connects to, shorting to earth?
there should be insulation around the bolt where it goes through the dist body and a couple of fibre washers under the bolt head and nut.

Did you install the earth wire that connects to the points ?

The dist body is earthed and I think the green wire will be an earth too, hence a zero reading.
Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL #114, auto, ps , 717,717
best of the best

ja17

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Re: Puzzling electrical problem
« Reply #4 on: February 06, 2010, 15:06:04 »
Hello Bob, and Walter,

Normally the factory transistorized ignition has the clip type connector for the ignition points. Bob is correct on the earlier cars with the little bolt and nuts, they must remain insulated as it passes through the distributor wall.

Always check the ballast resistors, and go through the test procedure for the "spark box" (transistorized ignition). The coil is wired differently on these transistorized units than on the standard. One side is wired directly to earth as I recall.

If you determine that the box is bad, you can convert to an aftermarket electronic, or find another good used box. The exact same box was used on all the six and four cylinder sedans of the era (1970-72).  The V-8s are different.

In an emergency you can rewire the distributor to standard ignition with no electronic box. Disconnect the ground wire going to the coil and leave it off. Run a hot wire from the ignition to the positive post of the coil then  then connect the ignition contact lead of the green from the distributor to the neg. (earth) side of the coil, as with std. ignition. I think you will need to slightly ream out the ring terminal on the green wire so that it fits over the distributor connection.   At least a 1.8 ohm ballast resistor must be added in line before the coil so the points won't fry. The original ballast resistors are not enough. You can use them both in series before the coil in an emergency. A more permanent fix would be to wire as above, and use the correct red coil and 1.8 ballast resistor and your original distributor will work fine.  The advantage of the factory transistorized ignition, is the points last much longer, you will loose this advantage if you convert to standard ignition.

So what happens if one of you guys are out on the road and your factory electronic box goes out ?  Wire as above and use both your original ballast resistors in series before the coil wire. Take about 15 minutes. You are basically bypassing the spark box and temporarily rewiring the ignition to standard.  The ballast resistance is not high enough for the coil so the points may only last a few weeks this way. But you will be able to drive your car home!!  All modifications are easily changed back to original when you get the parts for a permanent repair.

« Last Edit: February 06, 2010, 15:12:09 by ja17 »
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
2002 ML55 AMG (tow vehicle)
2002 SLK32 AMG (350 hp)
1982 300TD Wagon turbo 4spd.
1963 404 Mercedes Unimog (Swedish Army)
1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback

Richard S

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Re: Puzzling electrical problem
« Reply #5 on: February 06, 2010, 16:41:53 »
In 1998 I had the 30 year old original box go bad on my 250SL.  I replaced it with a NAPA Echlin EAS-70 Electronic Amplifying System and it has been runing fine for the past 12 years/20K miles.  Probably not a fix for the purist but certainly solved the problem for me.  I also use the same system on my 280SE 3.5 with excellent results.  I don't know if NAPA still has the EAS but I'm going to check and buy a spare if they do.
Richard
250SL RHD
Midnight Blue

waltklatt

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Re: Puzzling electrical problem
« Reply #6 on: February 09, 2010, 17:41:34 »
Thanks Richard, JA17, Hands_aus, MBZE, NAJ for your advice.
I have followed the varying lists of checking out the items.
Took everything out and checked it, all wires and connections seem tight and clean, or cleaned again.
Took the ignition box apart and everything is coated with a brownish red substance like paint and looks fine, a bit of yellowish/whitish powder arouns one of the openings.  Maybe bad?  No foul or burned or overheated smells from the circuits.
Put everything all back together, and now no spark at all.
I just put the car back together and put it outside under a cover for now as punishment.
Then it snowed 2 feet.
The garage is now clear again so I can make the new queen sized bed for my wife and I.
Have been waiting to get the car outside so I can do the bed for the last 2 months.  But the last thing left is to get it running again before the shakedown cruise.
But this snow?  Not likely anytime soon, and yet more coming tonight.  Whew!
THanks again for your suggestions, but they will be on the backburner for now.
Walter
1967 220SL-diesel-fired right up
1970 280SL-not cooperating with running.

graphic66

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Re: Puzzling electrical problem
« Reply #7 on: February 13, 2010, 17:36:53 »
I put the Velleman unit on my 230SL. It works incredible and can be reverted back to points in a minute. I put it over the shock tower under the plastic cover. It still uses the points, but just as a very low amperage switch and it eliminates the condensor. I would guess this is the same type of system used on the late W113. It costs about $35.00 and takes circuit board soldering skills, very basic though. Anyone with a good soldering gun and electronic solder could make this unit from the kit. I bought it just for the fun of building it with my Grandaughter, but this thing really works. I think I am going to get one for my Farmall Cub tractor, they have a 6 volt unit. My points were in need of replacement and when I put this unit in with the old points things smoothed right out. I am still going toput in new points this Spring though.
   I think this unit may fix your problem Walt, it may also fit right in place of the stock unit.
 Here's the link http://www.vellemanusa.com/downloads/0/illustrated/illustrated_assembly_manual_k2543.pdf

waltklatt

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Re: Puzzling electrical problem
« Reply #8 on: March 09, 2010, 05:07:58 »
Thanks to all who offered help on the puzzling problem.
Got it sorted out, just fired it up about 2 hours ago.
It's always the smallest thing that will stop it from doing what it's supposed to do and I found it.
Now my sledgehammer can go away back into it's proper place.
Tools can be repaired back to their places as well and my pride can come back to me.
Ahh it's a good feeling to be firing again.
Walter
1967 220SL-diesel
1970 280SL-"It's alive"

Naj ✝︎

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Re: Puzzling electrical problem
« Reply #9 on: March 09, 2010, 07:35:22 »

It's always the smallest thing that will stop it from doing what it's supposed to do and I found it.

Walter
1967 220SL-diesel
1970 280SL-"It's alive"

  ???   So, what was it?  ???

naj
68 280SL

Jordan

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Re: Puzzling electrical problem
« Reply #10 on: March 10, 2010, 12:28:04 »
Yes, after having read the thread I would also like to know what the problem was. ???  After all the back and forth, enquiry minds want to know. ;D ;D
Marcus
66 230SL  Euro 4 speed

waltklatt

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Re: Puzzling electrical problem
« Reply #11 on: March 10, 2010, 18:44:47 »
The small thing can beset the best restorations.
In this case it was the grounding of the coil.  It's not supposed to be grounded. 
That's the small thing that prevented the car from running.
Thanks.
Walter