Tach dies when lights turned on, no temp gauge.

[Roysneon]

As the title says, after my M50 swap the tach works fine, reads what I believe to be correct but then when the headlights are turned on and the cluster lights kick in, the tach drops. The temp gauge is always non functional, and the wiring between the C101 and x20 is correct for it. Anybody have any suggestions?

The car is a 1993 318i touring (formerly m40 powered). I took the cluster out to change it to a 6 cyl. coding plug.

[Roysneon]

So as it always seems when I post questions, as soon as I posted this I found out that you still need to change the rearward temp sensor on OBD 1 motors. I thought it was only for OBD2...

Anyone have any thoughts on my tach dying out when lights come on?

[Gregs///M]

Inspect SI board batteries. If lithium batteries, which it probably is, they are at least 20 years old. If the batteries have not been replaced, I would look into replacing them. Signal for tach runs directly through SI board.

[Roysneon]

There is a break on the PCB, the copper actually burned? right through the paper and broke. Si batteries are old, but look to be in ok shape. Before I started messing with wiring everything worked fine.

Once I put another cluster in everything worked fine. Could the break in the PCB circuitry cause the tach and temp gauges to act up like that? The broken/burned part goes to the foglight indicator bulb. I'm guessing I'll need a euro PCB to get the rear fotlight indicator bulb back as well...