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Fuses

This component is part of Electrical Systems.

A Fuse (German: Sicherung) is a small device that protects electrical circuits and wiring against too high a current which could damage these devices or burn up the wiring. Overcurrent could be created by an inadvertent short circuit, or faulty wiring, or a faulty device.

The fuse protects against the high current by blowing and breaking the circuit. A fuse consists of a small, soft electrical wire of a certain rating (Amperage), at which current the fuse is designed to blow. If the wire is not intact, the fuse has blown.

Standard Fuses

NrRating (A)LeadDevicesRemarks
1830Entrance light, parking light, clock, passing signal light, map light, hand lamp socketAlways has power
22554Windshield wiper and washer, horn, cigar lighterControlled with ignition key
3854Control circuit for automatic gearboxControlled with ignition key
4854Fuel pumpControlled with ignition key
5854Turn signal indicator, reversing lights, fuel gauge, stop lights, brake indicator lampControlled with ignition key
62554Heater blower, automatic starting aid, electromagnetic starting valveControlled with ignition key
7858Right: tail light, parking light, license plate, dashboard lightsControlled with light switch
8858Left: tail light, parking light, license plate, fog lights (right and left)Controlled with light switch
9856aRight: head lights high beam, and indicatorsControlled with highbeam switch
10856aLeft: head lights high beamControlled with highbeam switch
11856bRight: Low beamControlled with highbeam switch
12856bLeft: Low beamControlled with highbeam switch

The Ignition is not fused.

A Radio will have a separate fuse (2 A) and can be switched on in Ignition key positions 1 (Garage) and 2 (Drive). In position 0 (Off) the radio will be switched off.

The additional fuse boxes, e.g, for the heatable rear-window (16A) and power antenna, may be located in the engine compartment.

Fuse card

Below is the fuse card (front & back) located under the cover lid of the fuses on the firewall, in the engine compartment, in front of the driver:

Fuse size

Caution: This is not intended to be a guide for any specific car or electrical arrangement. Be sure to have a professional or knowledgeable person assist or do the work if necessary. The wattages given below are for Euro style headlights but the method of calculating the required Fuse Size will work with any headlight style.

You open the fuse box on your prized Pagoda and see a mixture of fuses in various sizes and colors. Should you change to the original “Standard” sizes and colors to bring the car back to showroom condition? Maybe not, read on.

The Table above lists the Standard Fuse sizes installed in new cars with normal wiring and components. When lights or the electrical system are modified over the years, different size fuses might be required.

As an example, Fuse "8" on Line 58 is for the left Parking Light, Fog Lights, License (Number) Plate, and the left Tail Light. To know the correct fuse size, we need to know the maximum Amperage for this circuit.

To calculate the Amperage of the current on this circuit: add the total Wattage of all the lights on the circuit, then divide the Total Wattage by the Voltage (12 volts). The result is the total Amperage when all the lights are turned on at the same time.

Typical Watts on the Circuit protected by Fuse 8 with Euro Style headlights: Parking Light 4 watts; License Plate Light 5 watts, two Fog Lights (in the Euro headlights) 70 Watts; one rear Tail Light 5 watts. Total is 83 Watts. Divided by 12 (Volts) is 6.9 Amps. With this light arrangement, the Standard original 8 amp fuse should be adequate.

What happens when a change is made by the dealer upon delivery or by a later owner? In this example, let us assume the owner of car with Euro headlights adds two Bumper Fog Lights, maybe vintage Hella style lights.

A typical vintage Hella Fog Light uses a 35 watt bulb. With the two added fog lights, the circuit would be carrying an additional 70 watts or a total of 153 Watts. Doing the calculation now shows the total possible amperage on Circuit 8 has increased to 12.75 Amps. As a safety measure, the Fuse Size should accommodate all lights on the circuit. If all the lights were turned on at the same time with the two new fog lights, the standard 8 Amp fuse would burn out.

The new fuse size for Circuit 8 with the additional load would be 15 or 16 amps. A fuse of the proper physical size (1/4 inch by 1 inch) having the original style pointed ends to correctly fit the fuse holder would be a Red color 16 Amp CGS style fuse, available (January 2010) for 50 cents up. Returning to (or continuing to use) an original 8 amp fuse would invite danger and a blown fuse.

In addition to using the correct Amperage rating for the fuse, be sure that the Voltage rating of the new fuse is over 12 volts.

The photo is an example of an array of mixed original and replaced fuses. Fuse numbers apply from left to right in the photo. The ceramic grey fuses are original style fuses. The glass fuses are replacements. The missing fuse in Position 8 is for the Fog Light circuit. Originally an 8 Amp grey ceramic, it will be replaced by a ceramic Red 16 Amp to accommodate later added Bumper Fog Lights.

Conclusion: do NOT change an installed fuse to 8 amp or other original size to be “Correct” according to the Standard fuse sizes listed in MB and other Service Guides. As you can see here, electrical changes to the original lights or wiring may require a fuse with a higher amperage rating and going back to the original size can lead to problems.

Physical Size of Fuse

A standard size “vintage” fuse is 1/4 inch around and 31/32 of an inch long. (Actually 6 mm around and 25mm long, sometimes sold as 1 inch long.) The industry standard size code for the ceramic is “GBC”, for the glass is “AGX”. Glass fuses sold for newer cars are typically 1 1/4 inches long and will not properly fit the fuse holder. A one inch long Buss style glass fuse with flat top and bottom will fit the fuse holder and can be used if the fuse is of the proper amperage.

The two vintage 25 amp fuses found in the Pagoda fuse box at Positions 2 and 6 are shorter in length and slightly thicker around. These two fuse positions have a cap to hold the shorter fuses. The short 25's are getting hard to find. A ceramic 1 inch 25 amp is available in dark blue. Can be used if the cap is removed from the fuse holder.

Colors of Fuses:

Standard vintage fuses used in W113 vehicles are Ceramic White (or light grey) for both the 8 amp and 25 amp sizes. An upsized ceramic fuse at 16 amps will usually be Red while a Buss 15 amp is a clear glass fuse. A ceramic 25 Amp replacement for the short fuses, will be dark blue.

Inspection

Good idea to inspect each fuse. Make sure the fuse and the holders are not corroded, that the fuse body is not cracked, that each fuse is the correct amperage for that position. A fuse with too large an amperage rating will not give protection in case of a short circuit or other overload.

A fair number of the Pagodas on the road today have undergone electrical changes for lights, radios, antennas, newer radios, automatic windows, and other electrical devices. Don’t assume what wattage a circuit is carrying and do not slavishly follow the original Wiring Diagram. Best to trace the existing circuit and carefully measure all current on a line before deciding what size fuse to use.


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