88 735i keeps blowing fuse 5, instrument cluster lights out

[E32FAN]

You are SO CLOSE!

[schnell944]

Thanks! So, I appear to have identified the source of the short. After I removed the IHKA control panel, I found what appeared to be a disconnected terminal buried back there. I fished it out and found this long snake-like mess of wires that seemingly feed back in on themselves, all wrapped up in electrical tape (see bottom, left corner in picture below). One of the wires is GR/red. When I move this collection of wires around, resistance on the GR/red wire for the dimmer goes up and down significantly.
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IMG_3368.jpg
Next step, I'll dissect this and try to get a better look at what's going on. I'm really curious as to where this originally was meant to plug into. Here's a closer shot of what remains of the plug:
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And here's a shot of most of the wires related to this and their colors:
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Lastly, I also dug out what appears to be an amplifier adapter. Though it currently does not appear to be causing my problems, from my limited experience, it does appear to be poorly or at least untidily wired:
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[E32FAN]

It appears to be a PAC SOEM-4 https://www.amazon.com/PAC-SOEM4-4-C.../dp/B002XW2IC6
The original factory amplifier is behind the left trunk panel. ETM section 6500. The 10 speakers are wired there, so an aftermarket radio has to be wired back there.

[schnell944]

Bit of a false alarm again! After unwrapping the suspect bundle of wires mentioned above, there were no obvious issues. Moving the set of wires isn't changing anything in resistance.

I went back and completely removed the instrument cluster, instead of just removing x502, which is shown as being linked to the dimmer. When I disconnected X16 on the cluster, resistance at the gr/red wire for the dimmer rose to 2.6 ohms. When I then disconnected X16 and X271 together on the cluster, resistance at the gr/red wire rose to 3.7 ohms. Disconnecting x502 and x17 on the cluster had no effect.

With the cluster completely disconnected and all other wires re-connected/light switch on, battery disconnected, resistance is 1.6 ohms at fuse 5.

No obvious issues in the wires near the cluster area. Not sure what this might indicate or how this could be!

Also not sure why resistance at fuse five shows only 2 ohms instead of 6.5 ohms now when I disconnect the gr/red and gr/black wires of the dimmer circuit. A bit confused.

[E32FAN]

Bit of a false alarm again! After unwrapping the suspect bundle of wires mentioned above, there were no obvious issues. Moving the set of wires isn't changing anything in resistance.

I went back and completely removed the instrument cluster, instead of just removing x502, which is shown as being linked to the dimmer. When I disconnected X16 on the cluster, resistance at the gr/red wire for the dimmer rose to 2.6 ohms. When I then disconnected X16 and X271 together on the cluster, resistance at the gr/red wire rose to 3.7 ohms. Disconnecting x502 and x17 on the cluster had no effect.

With the cluster completely disconnected and all other wires re-connected/light switch on, battery disconnected, resistance is 1.6 ohms at fuse 5.

No obvious issues in the wires near the cluster area. Not sure what this might indicate or how this could be!

Also not sure why resistance at fuse five shows only 2 ohms instead of 6.5 ohms now when I disconnect the gr/red and gr/black wires of the dimmer circuit. A bit confused.

OK, I plugged a digital ammeter into my 1989 735iL at F5 and measured between 2.6 and 4.0 amps, depending on whether the engine was running or off, and the setting of the dimmer switch, dim or bright. 12/4 = 3 ohms.

1. Will F5 hold if you leave GRY-BLK and GRY-RED unconnected?
2. When you splice GRY-BLK and GRY-RED, does F5 hold?
3. Do you drive at night? LOL


Seriously, is this a tolerable fault? Personally, I do not drive at night so I could live with a dark dash. Just saying.

On an other note, I love the $50 Protomex MS2108A clamp ammeter because it can sense DC current in any wire you clamp onto. So you could unwrap the major splice X580 and test each wire to see where the current is flowing. But this is a big step ahead, perhaps not for you.

[schnell944]

Thanks, for checking on your car, E32FAN. I appreciate it.

1. F5 holds when grey/black and grey/red are disconnected.
2. When they are spliced, F5 does not hold.
3. I do drive at night Even if I didn't, I don't think I could let this one go. I'm nothing if not stubborn. I only have a little time each night to work on this problem, but I'll keep working it until I figure it out eventually. I'm fortunate to have a small garage and two other (currently) working old BMW's to get us around.

My multimeter has a built-in clamp ammeter, as well. I figured it wouldn't be incredibly useful in this case since it at least appears that the problem is isolated to the dimmer circuit, per answers to 1 and 2 above.

I feel like you had a few other components to check compared to what I listed in post #50, but that content seems to be missing now from post #51 in this thread.

Still wondering what the E41 dash light might be - I'll disconnect it if I know what/where it is. I've pulled the fog instrument cluster, fog light switch, radio, IHKA control panel, program switch, hazard lights switch, and will move on to the OBC shortly just as soon as I can figure out how to remove the metal surround that holds the aftermarket radio in, which will allow the release lever for the OBC to be pulled.

I'll keep at it!

[E32FAN]

Thanks, for checking on your car, E32FAN. I appreciate it.

1. F5 holds when grey/black and grey/red are disconnected.
2. When they are spliced, F5 does not hold.
3. I do drive at night Even if I didn't, I don't think I could let this one go. I'm nothing if not stubborn. I only have a little time each night to work on this problem, but I'll keep working it until I figure it out eventually. I'm fortunate to have a small garage and two other (currently) working old BMW's to get us around.

My multimeter has a built-in clamp ammeter, as well. I figured it wouldn't be incredibly useful in this case since it at least appears that the problem is isolated to the dimmer circuit, per answers to 1 and 2 above.

I feel like you had a few other components to check compared to what I listed in post #50, but that content seems to be missing now from post #51 in this thread.

Still wondering what the E41 dash light might be - I'll disconnect it if I know what/where it is. I've pulled the fog instrument cluster, fog light switch, radio, IHKA control panel, program switch, hazard lights switch, and will move on to the OBC shortly just as soon as I can figure out how to remove the metal surround that holds the aftermarket radio in, which will allow the release lever for the OBC to be pulled.

I'll keep at it!

Your clamp ammeter probably works for AC current only, like a special sort of AC transformer. The clamp ammeter I use also has a DC function, which is useful here!

There are 10 exit wires from splice X580 and 9 of these are fine. Which is #10? A DC clamp ammeter could ID this wire for you, if you bridge F5 with a lamp, so a limited DC current can flow.

You can reach into the radio opening to release the OBC lever. No need to remove the radio bracket sheet metal to get access.

There was a note in the service invoices about a crimped wire with pierced insulation? This might be the root issue. The 10 wires exiting X580 only travel a few inches or feet. The S18 Hazard Switch is the farthest away, down in the console. Possibly one of the many GR/RT wires was crimped to ground somewhere. When you move wire bundles and see a change of resistance, that is the smoking gun to follow!

(Post #51 was a red herring so I deleted most of it.)

[E32FAN]

You could bypass the troubled wiring by running new jumpers from GR/BLK to feed the lights you most value - A2 Instrument Cluster, N4 On Board Computer, S18 Hazard Switch, say.

[schnell944]

Thanks, E32FAN. You're right, after taking a closer look, my clamp ammeter does not measure DC. I have, for the heck of it, ordered a sealed lamp and some extra wire/alligator clips to make a lamp tester as a simpler indicator of the presence of a short, in addition to my multimeter.

The only gr/red wire coming from X580 I haven't been able to identify is the one feeding "E41 dash light" at X543.

I'll keep at it as I'm able to steal away some time in the garage.

Your clamp ammeter probably works for AC current only, like a special sort of AC transformer. The clamp ammeter I use also has a DC function, which is useful here!

There are 10 exit wires from splice X580 and 9 of these are fine. Which is #10? A DC clamp ammeter could ID this wire for you, if you bridge F5 with a lamp, so a limited DC current can flow.

You can reach into the radio opening to release the OBC lever. No need to remove the radio bracket sheet metal to get access.

There was a note in the service invoices about a crimped wire with pierced insulation? This might be the root issue. The 10 wires exiting X580 only travel a few inches or feet. The S18 Hazard Switch is the farthest away, down in the console. Possibly one of the many GR/RT wires was crimped to ground somewhere. When you move wire bundles and see a change of resistance, that is the smoking gun to follow!

(Post #51 was a red herring so I deleted most of it.)

[schnell944]

For what it's worth, I re-connected all components and the battery and was able to turn the light switch on without shorting fuse 5. Annoying to say the least since I know I didn't actually fix the problem yet. I watched the resistance go down from 3.5 to about 2.4 ohms as I re-connected everything. Reconnecting seemed to have a cumulative effect on resistance, with the re-connection of the instrument cluster having the most dramatic downward effect.