Can anyone help with a starting problem on a 1989 740GL with automatic transmission?

I recently did some rework on this vehicle, including: replacing motor mounts and the transmission mount, new brake rotors all around and new exhaust system. In completing the motor mounts I removed the usual intake stuff and took the time to clean the oil breather box and other miscellaneous items. I also disassembled and cleaned the starter wiring. Just some good preventive maintenance!

After reassembly of everything and re-charging the battery, I found that I could not turn the engine over from the ignition. I rechecked the starter wiring with no problems found. I was able to engage the starter by jumping the terminals on the solenoid. I noticed that there is an audible "click" in the relay panel when I turn the ignition to start. My manuals do not show a specific relay for the starter solenoid, so I am somewhat stumped. I pulled the neutral safety switch out and checked it out as OK. I even jumped this switch with no success in starting with the ignition key.

At this point the only way I can start and run the engine is by physically jumping the solenoid. I know that there must be some simple connection, relay, fuse or whatever that I am missing and would appreciate any help offered. I am also suspect of the ignition switch itself, but this has never been a problem on the vehicle (intermittent or otherwise), and I am reluctant to pull it out right now. Once the solenoid is jumped the engine runs fine.

I have worked primarily on 240's but I would suspect that the wiring circuit and harness is similar to my 89 240. My first guess is that the cleaning of the starter wiring broke the blue yellow wire leading to the solenoid (terminal 50) within the harness. You can isolate the location of the break/short by tracing back from the solenoid to the ignition switch. First disconnect the solenoid lead (blue yellow wire) and attach a voltmeter to see if 12v is or isn't present when you turn the ignition to position III(just to make sure there isn't a short somewhere). Given your symptoms 12v should not be present. Next, look for a large gray rectangular plug as part of the wiring harness on the engine firewall just below the middle of the windshield (should be near the oil and transmission dipstick). This plug connects the portion of the engine harness that leads to the fuel injection and the starter solenoid. Immediately next to this larger plug should be a spare lead with a black plug that one could plug another lead into; it should have a blue wire coming into it (from terminal 50 of the ignition switch and a yellow blue wire that goes to the starter solenoid). This plug is a remote start access point; by running a lead from the + terminal of the battery you should be able to start the car. So you can either check the continuity from this plug with the lead that plugs into the solenoid (be sure to lead it unplugged at the solenoid) or apply 12v to (with the solenoid lead plugged in) it to see if the starter engages. If continuity is not present then the wire is broken within the harness. You should also check to see that this lead is indeed receiving 12v from the ignition switch by connect the voltmeter, turning the ignition switch to position III (12v should register only in the III position and not the II). If you find that these contions are present then you have found the problem. You can then run a wire from the remote start access plug to the starter solenoid terminal 50 as a fix without having to replace the whole wiring harness.

If however, continuity is present and 12v at the remote start access plug is not present you will have to trace back to the ignition switch. If you already located your automatic interupt switch, I would use the voltmeter at this point to see if 12v is coming out of the ignition switch. You can work back from this switch to another connector in the engine compartment (should be on the right had side of the driver compartment next the to heater fan) that has two blue wires (one from terminal 50 of the ignition switch and the other goes to the remote start access plug in the engine compartment) and a blue yellow that goes to terminal 30 of theJetronic unit). It is also distinguished by a black "loop" wire that plugs into the top of the connector. If you do not get 12v at this point when turning the ignition switch on to position III, I would then remove the ignition switch and test the terminals.

Hope this helps.

My update:

Right now I am still starting this car with a push button switch in the cabin. I just ran jumper wires off the solenoid. It is a solution, but I would prefer to get back on the ignition switch itself.

Regarding this response: There is not +12V at the blue/yellow lead that connects to the solenoid, so I likely do have a break somewhere. I recall when I cleaned the oil breather box that I had to "muscle" the cable harness out of the way to get the box out. I may have broken a wire then.

I could not locate the black plug referenced in this response. Must be that the 240 and 740 differ at this point in the wiring. I did locate the pink wire and black plug referenced in the next response, but found that this lead was +12V all the time, not just when in the III position on the ignition switch. ????

I could now use the color codes for the wires at the point where the cable harness connects to the plugs in the far right corner of the engine bay against the firewall. There are two large plugs and three small plugs located here. There is a blue/yellow" lead is here coming from the engine side of the harness and on one of the larger plugs. When I tried to run a jumper from that lead to the solenoid it did not solve the problem.

Any more ideas?

I appreciate the help!

Based on the other replies it appears you should be looking for a blue green wire on the engine compartment wiring harness since that matches the solenoid lead. And it sounds like the service socket has a pink wire (not blue green and blue) and is located by the left front fender. Did you get continuity between any of these points (i.e. service socket or harness plugs) and the solenoid lead? If not then the wire is broken in the harness. You should not be getting 12V at the #III position for the lead you tested if it is the service socket; that would mean that something is amiss with the ignition switch.

There is not +12V at the blue/yellow lead that connects to the solenoid, so I likely do have a break somewhere.

Wire colors are very different between 200 and 700 cars. You have no B/Y wire to the starter solenoid. It is probably Blue/Geen, as shown in my '93 940 diagrams. (900 and 700 are essentially alike, and common circuit wire colors stay the same over many years.

The "Service Socket" on my car has a Blue plug on the end of the pink wire. Yours may have a Black plug, but it should be in the same place (next to the air box, with barely enough slack wire toget at the female flat terminal. There shold be no +12 there untin the ignition switch is turnned to III.


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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

I could now use the color codes for the wires at the point where the cable harness connects to the plugs in the far right corner of the engine bay against the firewall.

Here's how it looks in the maker's manuals: Russian 740 map
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Art Benstein near Baltimore

I don't have the '89 diagram, but assume that my '93 940 will work.

Find the Service Socket (pink wire, Blue plug) on the left inner fender near the front, and

See if there is +12V there with the Key in Start position III.
= If no voltage, the problem is between there and the ignition switch.
= If there is voltage there, double-check that the blue/green wire terminal is secure on starter terminal 50 (not terminal 16, if present, which I doubt).

If the +12V isn't getting to starter 50, there are 2 connectors in the engine compartment left side, that are in the path from the NS switch. Let me know if you need pin/wire color to back-probe them.
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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

I appreciate the above response and those following. I am always amazed when I go to this forum for questions and get quick and helpful responses!

Since its' late on Sunday I will chase these circuits tomorrow and post a reply on my findings as soon as possible.

Nothing is ever simple, and you can't really rule out coincidence.

I assume you've checked the power from the ignition switch to the starter? run a continuity test from that wire to the ignition switch?