olmann

So I did something stupid. I had the ignition switch on without the car running and the blower fan running. I walked away for a (long) time and came back to a completely drained battery.

As the voltage drained and the blower kept trying to go it melted the blower motor fuse a bit. I pulled and cleaned/repaired everything at the blower fuse and checked everything else on the CE panel. I put a full slow charge on it and everything is functioning properly, except for the volt meter. It will go from 12 to 13 to 11 while the car is running. System voltage on the sharktuner shows steady 13.4 volts while driving. The voltage meter always stayed around 13 previously.

Any ideas where to look to find the fault or did I fry the gauge?

Thanks

olmann

The car in question is my 91 GT.

Alan

This sounds like a problem with the alternator. If your event did cause it - it was an indirect thing, likely due to the battery taking excess current - even after you charged it. Older batteries do not take a full discharge cycle without damage - it will never fully recover. Monitor how its going.

I suspect though that it is unrelated and just coincidental, even with a poor battery the alternator should be able to maintain >12.6V under most normal conditions. You may need new brushes in the regulator or a new regulator... since it seems like it works some of the time. Check the exciter circuit also - through the 14 pin connector - to make sure its not a simpler fix still...

Alan

olmann

Thanks for the response, Alan. The thing happening here is that the voltage is not changing, just the volt gauge is being erratic. I had a Sharktuner plugged in the entire time while driving and the voltage is staying rock solid. Today it was holding at 13.1V at idle after a hot drive but the gauge showed 11V. I checked the 14 pin connector and all of the wires look great. The engine has a new wiring harness.

One thing that is odd is that if I turn on the lights, the gauge jumps right up to where the output shows on Sharktuner. I'm thinking that maybe I have a marginal ground on the #2 connector on the instrument cluster. I will probably dig into that tomorrow.

Thanks for the reminder on the battery. May just need to go get it replaced.

Appreciate the feedback!

Alan

Sorry - missed what you said about the sharktuner. I'd still say its likely unrelated - check the grounds at the pod and the connectors (use an electrical connection cleaner/promoter/protectant).

I'd also use a DVM on the CE panel supply (B+ top connections) - the ECU's (and therefore Sharktuner also I assume) get a clean supply more directly from the battery than the rest of the panel - check the CE panel grounds too.

Alan

olmann

Will do! Thanks

olmann

I believe I have figured it out. I was thinking I had an issue within the cluster itself or maybe at the connector going into the cluster. When I pulled the cluster I checked incoming grounds and power at Plug #2. All good. So I took the back panel off of my cluster and put it on a spare one I have. Everything worked! Ok, so I'm thinking that my printed board that supplies power to the cluster lights and gauges is bad. I swapped boards, reassembled and installed. Did a quick check and the same issue was back. Hmmm. As I was thinking about it I realized the one thing that was different when I initially swapped clusters was that there were no cluster light bulbs installed. I pulled the bulbs and checked again and the gauge was back to normal. OK, my issue is something else. So now I decided to check the power and grounds coming in with the gauges plugged in and the power on. The incoming power for the gauge was low but the power for the cluster was fine.

I then traced the wires that fed the gauge back to the CE panel, Plug O. The wires there were reading low also. Following the schematic I found the wires went to Fuse 39 which powers the cluster. I had recently done a Deoxit treatment to all of the fuses and since I had power to the cluster I didn't think there was an issue there. I pulled the 5A fuse and there was some oxidation still and overall dullness. I measured resistance and did see a small amount. I went and got a shiny new fuse and installed. Problem solved! So after many hours of disassembly/reassembly work and following all of the wiring schematics, all I needed to do is make sure I had a nice clean fuse. This just further reinforces everything said here and on other threads about CE panel maintenance. I was happy to have figured this out as I had this issue on another 928 for years that drove me crazy and that I had never taken the time to figure out.