Alright leathermang showed up just in time for me to remember to slow down. Took the plugs out, sanded down all the connections, hooked them up on a piece of wood on top of the motor, and got readings from 11.5 volts down to 2.5 volts at #1. So I needed to clean them. Headlights work but heats up #30 to switch. The connection on the switch wiggles and Sparks, it's pretty toasted. I'll test the resistance across it, but prob should replace it. Fuses 2-6 is the cluster, currently diving in. 7-12 is the lights.

I'm at a loss why I'm getting ground to the fuse box. Same results with the switch disconnected. #30 is fine, no grounding.

Test light hooked to positive side of battery.




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You need to take it slow. These cars have very reliable electrical systems. I've owned a Jag so I've seen awful first hand. Your car is the antithesis of a Lucas electrical system.

If you're seeing sparks at the circuit 30 headlight connection you have a poor connection which will create resistance. Anytime you have resistance in a high current (amps) circuit like circuit 30 you'll have heat.

The wires for circuit 30 need to have crimped and preferably soldered ring tongue ends. They should be connected to the headlight switch with tight screws and lock washers.

I would fix the wires and replace the switch with a good used one. You can find one in 107, 108, 109, 114, 115, 116, 123, 126 and 201 cars. This range of cars covers about 30 years of production.

The fuses for your car can be found at you local auto parts store. Mine has them in stock. The Mercedes mentioned above will be full of them and they often have spares in the glove box. I just found some new ones in a 116 today! Don't change the fuse box. If you think you have problems now you can't imagine your difficulties after trying that!

Forget resistance testing too. It isn't useful here. Just check for voltage. Any circuit will show resistance to ground on the hot side because the circuit being tested is grounded. For example: If you measure resistance from a headlight fuse to ground the meter will measure across the filament to ground just as though you were testing the light bulb itself. Everything powered is also grounded. Also meters can be damaged by making resistance checks on a live circuit.

Your glow plug test out of the engine looks good. The salt shaker takes time to become visible. It may take 45 seconds before you can see it glow. If you have power to the glow plugs when pulling the gorilla knob to the glow position then the salt shaker is good or bypassed already. Make sure the heavy braided ground wire on the glow plug closest to the front of the engine is good.

__________________
1969 220D 5 Speed (OM616)
1983 240D 4 Speed
1985 300D Auto 376K
1985 300D Auto 275K

lol, I tend to over think things and get paranoid. Finally settled down, and told myself "man you have a bad glow plug, relax." And reality was the connections were dirty as all heck.

I got them back in the salt shaker warmed up as should. Car started right up.

The actual terminal on the switch is loose and moves. I'm glad to hear they are common, I'll call the junkyard tomorrow. I was just gonna get a universal one but here are two wires on their that I don't know what they are.

So when I'm running my test light, hooked to positive on battery, to the fuse box, I'm getting ground through the filament in the bulb. That makes sense. Finally. I knew I wasn't understanding something because nothing is melting or blowing fuses.

After going through the FSM I understood the workings of the series glow plugs, in that they have the juice run down the center, then back up an intermediate layer, and the outside is not grounded or connected to this circuit. Finally got a proper resistance reading. As well, I played with the set that caused the initial problem. I held my voltage meter to the outside of the plug, touched the positive contact to the battery, and my negative lead of my meter to the battery. I got full voltage on 3, half on one of them. So they were full shorting. This junkyard motor must have been on the shelf awhile. Or someone fried their glow circuit, towed it to start, and took it to the yard.

An old lady turned the car in for the california rebate for old vehicles. No rust. The owner almost cried. As per law he had to crush it. But I got the motor first.

I did take my resistance readings with the battery disconnected, but only because I thought it was accurate. Didn't know I could hurt my meter. Which would make me cry cause I finally bought a nice one.

Thanks for the help. I learned a lot. And even though I went through a lot for no reason, I know how the whole wiring system works, where it's located, and a lot about working on any electrical system.


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Long term build thread

1970 220D in for the long haul


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