Dead tach+OBC, other strange electric issues--not fuses, bad ground?

[TSI]

I took my e30 out of storage last week, and noticed a couple of strange electric issues, which I need guidance in solving.

Here are the symptoms:
1. tach+mpg gauge are completely dead.
2. OBC display dead. The backlight works, but no info is displayed
3. Radio resets every time I turn the car off--it asks for the unlock code but my station presets remain.
4. Interior light works on one side, not the other (bulbs are good)

What I've done so far:
Replace fuses 10,12,21,27 with new units (all fuses in the car are new)
Disconnect radio and reinstall
Change SI board with brand new unit (tested in another car, cluster is fully operational there)

I'm led to believe that there is a grounding problem somewhere, but I'm not sure where. I have seen many threads with dead tachs, obcs and radios, but they seem to be fixed with fuse replacement. The fact that my radio works fine but resets seems unusual in that context.

Everything worked fine in September (when I parked it). The battery (new last summer) did discharge a bit over the winter, it took a 20-minute 6-amp charge to get the car to start with no issues thereafter). Not sure if that's pertinent.

Any ideas?

[MusikAffe57]

check your reverse light cable

I have the same problem. Does your reverse lights work? check to see that the wire under your shifter isn't shorting against the body. I think it's also on fuse 21.

[efficient]

I had a problem like this. After I replaced all the fuses I found that one of the big black squares by the fuses was loose. After taking it out and pushing it down I noticed that I never had that problem again

[TSI]

I have the same problem. Does your reverse lights work? check to see that the wire under your shifter isn't shorting against the body. I think it's also on fuse 21.

Yes, reverse lights are fine.

I had a problem like this. After I replaced all the fuses I found that one of the big black squares by the fuses was loose. After taking it out and pushing it down I noticed that I never had that problem again

One of the relays? Thanks, I'll look into that today.

[TSI]

Checked relays and changed their positions, no result.
Also pulled radio and disconnected it, nothing either. Checked ground above clutch, it's fine.

I'm stumped :(

[Gregs///M]

The ground wires are located above the brake pedal on a metal bracket with two 10mm nuts and a bunch of brown wires going to it. Take the nuts off and wire brush every brown wire ring lug, then reassemble.

[TSI]

The ground wires are located above the brake pedal on a metal bracket with two 10mm nuts and a bunch of brown wires going to it. Take the nuts off and wire brush every brown wire ring lug, then reassemble.

Done. No dice :(

Some worsening though: now I have neither interior light, and the radio won't accept the code at all (still asks on every start)

[TSI]

Bump, any more ideas?

[TSI]

Still no worky, tried replacing interior lights.

[rcsoundn1]

Bump to get an answer here, this is an odd issue

[TSI]

Radio started working again, but still asks for code on every startup.

[TSI]

In a bizarre and perplexing twist of events, everything started working perfectly tonight. Tach, obc and econometer all at 100%. I have no explanation.

[TSI]

And we're back to square one as of the next morning, everything is dead. Two variables I can think to isolate:

1. I parked outside and it rained pretty hard (no driving in rain though)
2. I left my dashcam plugged into the cig lighter for about 7 hours (usually unplug it when I park for more than 5 mins)

I doubt they have anything to do with the instruments, but hey...