I am trying to chase down an electrical issue on my 91 240. This is what I have done and what has happened electrically since I bought the car.

1. Replaced battery (old was dead)

The car is in storage and was started routinely. After a couple weeks of this, while I was letting the car run on my usual startup, it died. I jumped it and it stayed running for about 30 seconds then turned off again. I had to then tow the car back into the garage as it wouldn't stay running long enough to get it there (about 100 ft.). I then fully charged the battery so I could move the car again. I did the battery cable alternator test to check the alternator and the car died when I removed the negative cable.

2. Replaced alternator with a used one

I thought this would do the trick but after a couple weeks the car died once again. This time the car seemed to stay running after it was jumped, but I don't think the battery should have died in the first place.

I am not sure where to start. I do not know if this is related but I will point out that the dash lights to not work as well. I also after purchasing the car replaced the instrument panel as the odometer and speedometer did not work at the time. Those are now working with the new panel.

Am I looking at chasing a short in any number of the wires in the car? Could that be draining my battery somehow? Thanks!

 

step 1 is to verify the alternator is charging. first, key on without starting, does the ALT/BATT red light come on? it should. if it doesn't, check the D+ wire to the alternator. verify the ALT light is good by disconnecting the D+ wire, and connecting said wire to ground, and switching on the key, if the light doesn't come on, check the light bulb in the instrument panel.

now start the engine, does the ALT/BATT light go out? if it stays on, your alternator probably isn't outputting sufficient voltage (or any at all).

the ultimate test is to measure the voltage of the battery before starting the car (and after its sat an hour or more). A fully charged battery at 68F should read about 12.6V, but if its very cold, it will be significantly lower. Now start the engine, and measure the voltage again. the 2nd voltage reading should be about 1.5V higher than the first voltage, like 14.1V if the first reading was 12.6V.

 

Thank you for the response! I have since figured out the problem and everything seems to be in order!

 

well, what was it ?

 

To be honest, I am not entirely sure. I dont have the best working knowledge of automobile electronics so when my friend that helped me explained it I was a little in the dark. He told me he had to manually "jump" the alternator to get it to charge properly. I guess it was not charging as should be, and he did something to restart it. The car has been run several times since, and have had no problems with it. I drove it yesterday on the road and didn't have an issue with it. I am going to keep your instructions on hand as these problems can linger as I am sure you know. Hopefully it is all said and done!

 

sounds like the D+ alternator/battery light circuit isn't functioning.

always, when you turn the key to 'Run', before starting the car, the alt/batt light should light up. when you start the engine, it should go out.

the indicator light is actually part of this D+ circuit which provides the 'bootstrap' current that wakes up the alternator charging. a bad indicator bulb, or broken/disconnected wire, and the alternator won't start.

 

Here is something for you. I did notice that the light that illuminates the entire instrument panel so you can see it at night is out...could this have something to do with it? I have yet to figure out where the location of this bulb is to replace it but that is my next thing to do.

 

there's a couple of those bulbs for the instrument cluster illumination, but they have nothing to do with the indicator lights.

question: does the dashboard dimmer dim the rest of the dash lights (switches, shifter, etc) ? if ALL those are out, its possible your dash dimmer circuit is out

 

Good question. I will have to take a look next time I get back to the car. I actually want to say the rest of them do not work. How do you go about replacing that circuit?

 

well, you start by troubleshooting it with a multimeter.

turn the lights on and you should have power at fuse 16 (which is also the parking and tail lights).

on the 240s, the fuse panel, on the right side, there's 3 spade lugs next to each fuse. the back/right most one is the 'input' to the fuses and is wired to the left side of the fuse. the 'output' of the fuse goes to the left/front, and middle spadelugs. some fuses inputs are wired together inside the fuse panel, for instance fuses 15 and 16 are both powered from the light switch circuit 58 via a white wire.

anyways. fuse 16 has a grey wire that goes directly to the dashboard dimmer pin 58b, if you connect your volt meter to this pin 58b and ground, you should see full battery voltage here if the light switch is in parking or headlights.

this same pin has a red-white wire that goes to the ash tray light, and the two seat belt latches (eg, they are /before/ the dimmer).

dimmer pin 58a is its variable output, this goes to brown wires that go all over the place, to the instrument panel lights, to the various backlit switches, the clock (if you have the seperate clock). If you connect the voltmeter to 58a and ground, you shoudl see a variable voltage depending on where the dimmer **** is set.

if all that is good, and there are STILL no lights, then I dunno, either all the bulbs are gone, or the dash wiring is really messed up. Note that botched stereo installs can fry the rheostat, as the factory radio is wired to it also, and if someone misconnects that brown wire, it can burn out the rheostat (few aftermarket radios support a dashboard dimmer circuit).

 

I will have to give that a shot when I get back to the car. Unfortunately the previous owner did install an aftermarket radio, something I am not a fan of. I will let you know what I find out. Thanks again!

 

ALL my vehicles have aftermarket CD decks in them, and most of them have upgraded speakers. I'm not much of a fan of 25 year old cassette decks and crusty old speakers.

 

Yeah I hear you. I just like to keep the stock look and feel to the car. The bright green LED's on the aftermarket stereo don't really support the stock feel.

 

one stereo I had that was particularlly obnoxious, I took the removable front panel apart, and found hte various surface mount LEDs, and put dark nail polish over them, using a contrasting color (red LED got a non-red color like a dark green or blue, blue LED got red polish.... reason is, a red led will punch right through red polish). this dimmed the panel down to where I could tolerate it while driving on a dark rural road at night (I also keep my dash lights fairly dim when I'm in the country).

 

So Pierce, I didnt have time to look into it a whole lot as I was in a hurry when I went to start up the car. I figured that I would let you know that it doesnt seem like the any of the switch lights work in the car other than the seatbelt lights. Does this sound like a rheostat to you? Is there a fuse that powers all these bulbs? I hope to get back and take a better look at everything this weekend.

Something else to note...This is my 2nd instrument panel in the vehicle and I do not believe the lights worked with either panel in, not sure if that helps.

 

well, you troubleshoot this stuff with a volt meter and the wiring diagrams.

 

What do you mean by "switch lights"? Are you referring to all of the "idiot lights" in the cluster - meaning the battery, oil pressure, SRS, etc. indicators?

 

I'm assuming he means the backlight on the switches and controls.

 

Butchered wiring scares me more than anything, you can fix tasteless newer radios, you can replace old audio, only so much you can do the mend crippled wiring.

My current 240 got a bit of a splice job done, the newer front speakers and radios will operate but the aftermarket amp in the back wont, drains the battery dry too (though some of this might be the cheap radio one of the owners threw in).

I agree with trying to keep a cars interior "look", nothing dumber than a vintage Mustang with some tacky cd player shoved into it.