OVP question
 

The cruise, tachometer and oil pressure have all suddenly stopped working on my '89 300CE. I have removed the cluster and checked every connection and tested the fuse and made sure it was good. I then checked fuse #5 under the hood and it too was good. I read some old post on the diesel forums talking about OVP and cruise & tachometer. I couldn't get the relay to make any contact noise when I applied power to it. Also, when I shook it there is a rattling noise. Is this a sign of a defective relay? Does the OVP have any control on these items? The oil pressure gauge is pegged at zero whereas the tach does move upon startup but clearly isn't representing accurate engine RPM.

It is not connected, but if your OVP rattles I would replace it.

Sounds like the cluster is toast. If the tach is broken, no cruise, no A/C....

Double check the main plug that goes into the cluster on the left side (oil pressure side) hasn't broken or was put back on incorrectly. If it is not plugged in right, weird things will happen.

There is a grounding bar connecting the three pods (instruments, speedo, tach/clock) together and then to ground (pin 1 on your connector). If the grounding bar connections have corrosion and thus no ground, these items will not work. You can take your cluster apart and clean the surfaces.

http://i31.photobucket.com/albums/c3...r/IMG_0629.jpg

http://i31.photobucket.com/albums/c3...gerepair01.jpg

http://i31.photobucket.com/albums/c3...gerepair03.jpg

http://i31.photobucket.com/albums/c3...gerepair08.jpg

Yes, the main plug was my first thought and I double checked that it was secured. The A/C is working fine though. Does that mean my problem is somewhere else? I'm going to replace the OVP and clean grounds as per the post from Oldwolf above. The cluster was working fine before, it was only after the second removal that everything went haywire.

I changed the OVP to no effect but I forgot to check the cruise.

sometime back my oil pressure gauge when to zero ,the sender unit reading indicated normal oil pressure so i left it as is to replace on a free day. Surprising A few days later the gauge became re-operational ,and still is .a mystery.
mak

I'm going to clean the grounds up on the cluster and hope for the best. Cruise is still not working and I'm not really sure how it ties into this problem.

did you switch out fuse 5? sometimes they look good and they are not.

ask me how i know

Yes, that was one of the first things I did and tested it for continuity.

Grounds
 

I had related issues and could not find the break in the ground circuit. I finally resorted to running a ground wire from one of the metal screws off the back of the clock to a ground behind the cluster. The gauges all popped back to life with no issues.

Well I cleaned all the grounds but there was no effect. I then decided to add a ground and to my amazement the tachometer and oil pressure gauge came back to life. Unfortunately, as soon as I turned the turn signals or either the park or headlights on, both of the gauges went dead but would come back to life as soon as I turned them off. Where can I add a suitable ground that won't be affected by what is obviously the instrument lighting?

Anyone?

check the fuse

Already done as indicated in previous post above.

maybe the fuse connector then? it seems like everything you are describing somehow ties in to a piece linking all the malfunctioning parts. wouldn't a wire of some sort cause your fuse to blow? You said the fuse is still intact so it must be something else. when my tach, oil pressure, temp, and turn signals died it was because of an issue in the fuse box. I'm not disregarding what you have already said you did, just trying to throw out a simpler suggestion before you go into any extensive and unnecessary fixes.