starter solenoid
 

I recently replaced the engine in an 82 240d with a 5 cyl from an 80 300d (225k miles). Shortly thereafter, the starter solenoid appeared to have failed. I could jump it with a screwdriver but no action from the key. I then replaced the solenoid with the original unit from the 82 motor (294k miles). One time, I had to jump it with the screwdriver, but for the most part it cranked when demanded. Now, about 4 weeks later, it no longer cranks with the key, but does with the screwdriver.

I'm not too knowledgeable about this part of the system, so I'm no exactly sure how to test it. Intuitively, since they were both fairly old, it might be coincidence to have these failures back to back. However, I've ordered a replacement and if I am running the risk that the solenoids aren't necessarily at fault, but rather the victim of another problem, I'd like to know.

If I were to test the current solenoid, how would I go about doing so? Is there something else that could cause these to go bad? Or, is it more likely that this is coincidence and I shouldn't worry?

Thanks much,
Kenneth

kchristopher,

You might have a key switch that is intermittent in the start contacts. If connecting 12volts to the small screw where the key switch is connected to the solonoid causes the solonoid to work, I think your key switch is not working properly or there is a bad connection between the key switch and the solonoid.

P E H

Thanks. And the key switch fix would be corrected by getting a new cylinder from the dealer? I remember reading a bit on people having to swap these out.

Key switches fail but usually start to get flaky before quitting altogether.
Another possibility is the neutral sensing switch. I had one go out in a W123 300D half way cross the country. Can't forget that day! it was Christmas eve, in a podunk town in West Texas. After calling a tow truck which happened to be 80 miles away, I finally hit the key and it started! I cancelled the emergency road service and got the heck outta there.
I later bypassed the neut switch to get back home until I could replace it.
DDH

I don't see the neutral safety switch listed in the 123 manual website. Would you kindly guide me to the location?

If on an automatic it is located on the transmission, passenger side I believe. Has a round connector that carries a rather thin cable to it with a rubber cover to keep grease out. My rubber cover was half way off, and it had grease in it (rather lots of oil that collected dust the glop then got into the neutral switch)
If its a stick shift, it will be located under the boot near the shift gimbal (on the car's console)
The neutral lockout switch is wired in series after the key switch, to prevent being able to start the car while it is in gear.
BTW, simply flushing it out with WD40 or something might restore it functionally but I paid the $40 for it.
For price of the automatic trans neut switch see Fastlane, find your car, click on Transmission, look for Neutral Safety Switch (picture follows):



DDH

Chris and diehard,

I didn't think a manual transmission car had a neutral switch. None of mine did but the newest manual I have is a '75, so the switch may have been added after that.

If the keyswitch doesn't activate the starter, try wiggling the shift lever or move it thru the neutral position and back to park while holding the key to the start position. If the starter is then actuated, the neutral switch is the problem.

P E H

Intermittent bad ground connections due to corrosion, loose connections, and temperature effects can often cause some of these problems. Go thru all grounds in battery, starter, and related circuits, checking for corrosion and tight connections.

I just got through fixing the same problem you have. The secret word is 'ground'. Mine turned out to be a faulty ground from the wires that go from the start/run circuit to your starter relay (not the solinoid although a wire from this relay ends up at the solinoid). I have a 115/300d but I bet the starter circuit is not much different than on your car. My start/run relay is on the pass. side engine compt. firewall. It is mounted under 2 fuse blocks.

Unscrew the mount from the firewall, turn it over, and remove the rectangular plug from the relay. There are 2 relays there. One has a 4 prong plug and one a 5 prong. It is the 5 prong one you want. Look on the face of the plug (you'll be looking into the prong receptacles). Next to each hole is a number. If you get a small bolt that will just fit into the hole you can hook up jumper wires to the various circuits w/o removing the back of the plug.

My wiring diag. , a copy of which I got from a MB mechanic, shows the following.

Wire 1. goes from the relay to the starter solinoid. Touch this with a positive jumper and the engine will crank.

Wire 2. goes to the ac cutout system.

Wire 3. is the incoming start/run power supply. This circuit is activated when you turn your ignition switch to the no. 2 position. When the relay is activated by turning the ignition to the start posit. power from this wire goes through the relay contacts and out wire no. 1 to the starter solinoid.

Wire 4. is the incoming start power supply. This circuit is hot when you trun your key to the no.3 (start) position. It is the power that makes this relay work.

Wire 5. is the outgoing ground continuation of wire 4. It goes to the trans. neutral safety switch and then back up the same cable bundle to a common ground under the dash. On my auto. trans. the safety switch plug is on the driver's side right next to the trans. shift lever-not the shift lever coming down from inside the car. The connector plug is flat, about 3/4 inch thick and 3 inches tall. The safety switch itself is casing out of which the trans. shift arm comes. You can see the numbers 1,2,3,4 stamped on the front side where the plug goes in.

My problem was that this ground was intermittent. All the grounds end up under the dash in a snake's nest that looks like an explosion in a spaghetti factory. Rather than try to get into that (it can be seen very easily by removing the instrument panel) I decided to use a ground jumper. I spliced into the brown ground wire where it come out of the back of the plug and went to a convenient bolt on the engine. The car started as usual.

The only problem is that now the car will start in any gear. Given most drivers this shouldn't be much of a problem. The back up lights don't work but I think that is just a matter of installing another ground at the trans. After spending 2 weeks on and off in the S. Texas sun chasing this problem I think the above glitches are a small price to pay.

Wire 5 from the relay goes to the trans. plug no. 3. It continues through the safety switch and comes out throught plug no. 4. This wire goes back to the main ground under the dash.

Wire 2 in this plug operates the back up lights. It comes from fuse 5 in the engine compt., to the no. 2 plug, goes through the safety switch and out through no.1 plug to the back up lights.

Now that I look at this circuit I don't think that the ground jumper I installed would cause the lights not to work. Come to think of it this entire problem may have been caused by a faulty trans. safety switch. Well, there goes my Sunday.

Thanks guys. It actually started working again this afternoon. Maybe I leaned against something once when jumping it and helped the connection? I'll print this out and see what I can come up with this weekend chasing connections.

Oh yeah, I have moved the shift lever while holding the key in start to see if that would help and it never has.

Got in it this morning and it didn't work again. Looks like I have a few plans for this weekend.

I think you need to replace the actual starter....
I had these intermittant symptoms and PEH described how the electricity INSIDE the starter could produce them....the electricity has to go through the inside of the starter to get to the solinoid actuating dealybop ....
When they took it apart they showed me the sparking place at the bolts which hold the brush holder inside the starter....
Replaced the starter, perfect ever since....

My logic tells me that . . .if it cranks with the screwdriver it seems to me there is no problem with the starter. All the screwdriver is doing is acting like the key switch, the neutral sensing switch, and a bunch of interconnecting wires in harmony. There is lots of stuff external that can cause an intermittent. The screwdriver is bypassing all of those current paths, and if the starter acts immediately when the screwdriver is touched to the terminals, it should not be a suspect in this mystery. A set of clip leads with small alligator grips on the ends can be useful in this type of work. Bypass one thing at a time until you find it, provided the problem stays a problem, when it comes and goes like you say it has it makes troubleshooting harder.

Oh yes, when this sort of problem ensued on my 123, I used a wire with one end under the starter terminal that I used whenever I wanted to start the car.
When not in use it was taped and stored in a bundle of insulated wires coming off the battery.
It meant opening the hood and momentarily touching the battery to start the engine, of course the key had to be "on" in order to remove vacuum from the engine "kill" diaphragm but it worked while we were on the cross-country trip (just don't be embarrassed when you go out to start your car in front of relatives or at a roadside diner.)
In fact, I just recalled that it is still there, I left it just in case the neutral switch or key switch or whatever goes out again. This idea could be pressed into service to get you where you need to go this weekend, kchristopher. It might save a call to AAA.
DDH

I've actually entertained the idea of putting in a starter button. Nice big one with the red rubber button like the big rigs.

I'll chase down some grounds, but I may install a switch inside (hidden) for future use.