Tach & Speedo Not Working
 

1989 S4 auto.

I pulled the pod, cleaned all contacts, same with contacts in trunk.

Both speedo & tach worked before I opened the pod (did so to clean up fuel gauge contacts) so must be something I did, broke, overlooked.

Also now notice that the interior lights don't come on, & nothing displays when I use the steering column/computer levers. Plus, of course, the fuel gauge still doesn't work.

I have a spare Interior Light Delay relay, swapped out, but no change. Fuse appears good.

Any ideas?

Thanks,
Hawkeyes

Sounds like a ground issue. There are a ton of ground connections under the dash on both sides (MP IV and V). Chances are it will be ground point IV as that is common to both the dash and light problems you are suffering. The Instrument Cluster gets its ground from MP IV and runs to plug number 2 at pins 14 and 15 of the “Instrument Cluster”.

A simple test of this would be to check for voltage at one of your interior lights. If battery voltage at the light is present and the light is not functional, supply the light with an extra ground wire. You can do the same thing with the Instrument Cluster; just apply an extra ground to see if this fixes your problem.

Now if that didn’t fix your dilemma, I would say the problem you are having might be because you didn’t go far enough in your cleaning process. By this I mean, you only cleaned the outside connections (four plugs) and didn’t take the instrument cluster apart and clean thing up in there.

Also, while you are at it (WYAI), Porsche issued a bulletin saying that the ground wire to Bulb Control Unit was lacking, causing false bad bulb condition. To fix this, you permanently add an extra ground wire to your Bulb Control Unit. I have not done mine yet, but the book says that the Bulb Control Unit on the right hand side of the car (from the inside of car looking out) mounted to the parcel tray.

Something Porsche didn’t say; was that after 89 they upped the wire sizes on a lot of components in the 928.

Hope that helps!