Fried section of main board (right back light)

[Gaspa_14]

https://photobucket.com/share/ef32118f-fa56-44a9-9c02-75f1ac76b8e8

Hello, first time posting here. I have a 1987 325e with a fried section of the main board. Back story: I bought the car 2 years ago. It came with several main boards (including fried one in photo) and other cluster parts. when I bought the car the gauge cluster back lights didnt work. I took the gauge cluster out, and replaced both bulbs. That didn't fix it. turns out it was the headlight switch so i got a used one. It sort of worked. Only the left side backlight would turn on. So for the past year I've just been driving around with only the left back light on (only the speedometer and fuel gauge would light up). Also, about 2 weeks after I bought the car the MPG gauge stopped working. Today I finally got around to try to fix the MPG gauge (I have a donor gauge) and I pulled the entire cluster and I saw the board was fried in the exact same location as the one pictured. I'm using this photo of the older board because it's easier to look at the path of the wire, but the current cluster I just pulled from car with all the gauges on it is fried in the exact same way. So, it seems that It's just the "wire" going to the right back light bulb is the one frying. I never talked to the old owner about why the board he gave me fried, but I'm assuming its the same issue. Everything else on cluster still works (minus mpg gauge).

I think its either 1: its possible the fuse for the gauge cluster is too large/bad and isnt blowing when it should (and cooking the board) or 2: there is an electrical gremlin from the harness that's cooking it.

Thoughts? It's strange it's happened on the exact same wire twice. Any help appreciated.

TLDR: Second main board fried in the exact same way, I'm trying to figure out why.

[Vincenze]

It seems the traces go to the illumination lamps: plus and minus.
Moreover, they go to other illumination lamps, for example, in the clock.

If the amperage is too high, the traces overheat.

[Gaspa_14]

It seems the traces go to the illumination lamps: plus and minus.
Moreover, they go to other illumination lamps, for example, in the clock.

If the amperage is too high, the traces overheat.

Thanks for the response! Here is a second photo that is much clearer: https://photobucket.com/share/ba83b7...5-d57a98f9c864 Yes, the traces go to the right cluster backlight bulb. the two warning lights that the traces go through work perfect so it seems the only issue the burnt trace caused is the right backlight bulb not working. You're right about it being the plus and minus and you can see the exact pins on the harness connector that the short came from. Do the same pins on the connector also power the clock backlight? I'm trying to figure out how and where the amperage came from that fried the traces. Thanks.

[Vincenze]

Check the "Multifunction clock" section in the wiring diagram.

The traces go to the yellow connector. The clock is connected using this connector. You can see 2 brownish traces there.

[Gaspa_14]

Check the "Multifunction clock" section in the wiring diagram.

The traces go to the yellow connector. The clock is connected using this connector. You can see 2 brownish traces there.

I'll take a look and see what I find. Thank you!

[Vincenze]

The illumination bulbs can be too powerful.

[Gaspa_14]

The illumination bulbs can be too powerful.

I pulled the multifunction clock and both bulbs weren't blown, and they were the correct 1.2 a bulbs. I took them out and they both lit up off a 9V battery. I also took the cigarette lighter and ash tray light out and discovered that not only was the ash tray bulb blown, the plastic case around the bulb was cracked allowing the bulb to wiggle around freely. Also, the connector that the bulb plugs into had a crack down the side allowing the metal tab that the power wire goes to, to also wiggle side to side. Seeing how the ashtray light is on the same circuit (6300-1) maybe due to the bad connection shorted out and blew bulb? Looking back I do remember the tray light would flicker and sometimes not turn on or off.

[Gaspa_14]

[Solved] sort of. In my pursuit of finding the electrical gremlin that was causing the short/overload I unplugged most of the switches/accessory lights on the same circut as the cluster backlights (https://www.armchair.mb.ca/~dave/BMW/e30/e30_87.pdf figure 6300-1) . I unplugged the multifunction clock, ac+recirculate air button panel, ash tray light bulb, cigar lighter, and foglight switch. I also put a 5A fuse in place of the 7.5A fuse. Lastly, I put a light layer of dielectric grease on the tracers. I then plugged the cluster back in, and started the car. I turned the headlights on and turned the headlight switch rheostat up. Both cluster backlights lit up, as well as the remaining accessory lights I didn't unplug. I sat for about 4 minutes messing with brightness turning it up and down. I didn't smell any burning. I then shut the car off and unplugged and removed the gauge cluster. I opened the cluster up and the tracers were still intact and not burnt. I then reinstalled the gauge cluster and went on a 10 minute drive to a nearby store. Everything worked on the way there, I parked. I drove another 10 minutes home with everything working. The last 2 boards that fried, fried within like 30 second of the car being turned on, to the fact that after the 10 minute drives everything works, It seems to be fixed.
CONCLUSION: One or several or all of the 5 buttons/lights I unplugged seems to be the culprit, and was overloading the backlight circuit. I don't have the patience right now to test which was was actually bad, but I have a suspicion it was the ash tray light connector.