My son had a problem with our '90 240 last night. Apparently when he went to use the car, the instrument panel was not working. No idiot lights, no gauges, no instrument lighting. However, the car started and ran so he took it to work. On the way home he noticed the headlights getting dimmer and finally the car just died. I came over and jump started the car and charged the battery enough so we could limp home. On the way home he hit a bump and the gauges came back on and the lights brightened as if it started charging.

My first thoughts is that it seems like a bad ground on the instrument panel is most likely the cause for the guages and idiot lights not to work, but would it also cause the car not to charge the battery?

Also, does anyone out there have any pics, instructions for instrument panel removal?

Thanks in advance

 

I'm thinking it's the other way around...a bad ground on the alternator not feeding the cluster. I'm thinking your car doesn't have a volt gauge. As these cars age, the volt gauge increasingly becomes more of a necessity rather than a doo dad. The cost is minimal and the installation, even for a rookie, is less than an hour. As well, it is possible the alternator is failing. An hour with a multi-meter will speak volumes.

 

Would a bad ground on the alternator cause the entire gauge cluster to not work - or are you thinking that a low battery was the cause of the gauge cluster not to work?

In this case all the idiot lights (oil, battery, check engine, etc.) did not illuminate when the key is turned to the on position. Also, the speedometer, gas gauge and temp gauge did not work. You are correct, no voltmeter on this car.

The car started and ran fine with the gauges not working but the battery was not charging. I'll check the ground on the alternator but I am puzzled how this would affect the whole gauge cluster.

 

I would take a look at all the fuses, especially fuse #13. Then inspect the junction of all the red wires on the fender by the battery. If it still continues to happen, wiggle the key when it does - it could be the ignition switch.

 

I checked the connections on the alternator and the seem to be fine. So time for the trusty voltmeter.

Engine off - voltage at the battery was 12.5v (I charged the battery overnight)
Engine idling, no load - voltage at the battery was 13.9v
Engine idling, radio, wipers, blower, headlights on - voltage at the battery was 13.0v

When I revved the engine with the full load, the voltage climbed to 13.8v

Do these readings sound like a weak alternator? If so, what parts should I replace - brushes? regulator? full rebuilt unit?

Thanks

 

I really don't think anything is wrong with the alternator. I have the same above voltages. The problem was you didn't have power to the cluster, so the battery light didn't come on in KP2, so the battery wasn't being charged. But now things are working because of a intermitten connection .. which is probably the ignition switch or the positive terminal block (the two things shared by the alternator excite wire and the gas/temp cluster power).

 

That was my original thought - without the battery light working on the cluster, the alternator won't charge. I was kinda thinking that it might be the ignition switch but I can't check now since all is working well. I just took it for a drive and wiggled the ignition switch like crazy and it didn't cause the cluster to go off.

Like you suggested earlier, I checked the 25 amp fuse on the fender - it was slightly discolored but not bad. I cleaned it up again and used some dielectric grease on it. Took the cover off the junction box next to it (is this what your refer to as the positive terminal block?) but everything inside is nice & clean (I like to keep it that way).

I guess I am in waiting mode again for a failure to see what it may be. It's not my daily driver so I get a lot of my info second hand.

Thanks for your help. I'll keep you posted when I learn more.