Fuse 21 issues

[snaponbob]

I am working on an 87 E30 325i. The issue is that with fuse 21 in place, the left side turn lights are on as is are the left side markers and the left turn indicator. This persists even with the instrument cluster removed. Looking at wiring diagrams, this makes no sense. Any component on the F21 circuit has been isolated, or so I think. This issue exists with the key off or one.

Thoughts?

[spdracrm3]

interesting, as looking at the fuse details the only component even close to being shared by those two circuits is the Active check panel/module , have you dis-connected that yet (in trunk next to left lid hinge), other than that it could be a wiring shorted somewhere in the harness or if someone tied something aftermarket into the two circuits and that is causing an issue, obviously the fuse is the power source feed (that is hot at all times) but how it is getting to the park/turn circuits is a mystery

[snaponbob]

Okay, this will bake your brain.

Instrument cluster removed. No change.
Overhead check panel removed. No change.
ALL relays removed. No change.
Radio removed. No change.
Chime module and trunk light removed. No change.

[spdracrm3]

good start ,only by process of elimination will you find it ,hopefully not buried in a wire harness somewhere

try the check control module (rear light check relay in pic) as mentioned also if its and aftermarket radio install look closely at the new wiring job and see if anything is tied together ,gotta be on the lookout for strange stuff

[Andy Mechnic]

Is the left turn indicator in cluster lit?

[snaponbob]

Is the left turn indicator in cluster lit?

Yup. And with the cluster removed, the left turn lights and side markers are on solid.

[snaponbob]

good start ,only by process of elimination will you find it ,hopefully not buried in a wire harness somewhere

try the check control module (rear light check relay in pic) as mentioned also if its and aftermarket radio install look closely at the new wiring job and see if anything is tied together ,gotta be on the lookout for strange stuff

The picture is vague.

[Andy Mechnic]

You have a short to the left turn/ hazard circuit. Good place to look would be in the fuse box, or where it goes through the firewall. You're looking for wires that are likely chaffing on plastic since it hasn't blown the fuse. Might want to try unplugging the hazard switch and turn signal switch to see what it does.

[snaponbob]

You have a short to the left turn/ hazard circuit. Good place to look would be in the fuse box, or where it goes through the firewall. You're looking for wires that are likely chaffing on plastic since it hasn't blown the fuse. Might want to try unplugging the hazard switch and turn signal switch to see what it does.

Certainly aware that there is a true short. (The word is too often misused!!) It is fused at 7.5 amps, but one of those has no chance, as 10 amp fuses have popped.

So far, I have been using both the Bentley manual and the BMW Electrical Troubleshooting pdf for wiring diagrams. I have yet to see (in the diagrams) where the potential shirt could be. The only reference to F21 in the Bentley is on page 48 where it is shown supplying voltage to C1 (blue plug) pin 2 at the cluster, but the PDF shows that cluster is basically in parallel to ground on the circuit allowing it to monitor the left blinker circuit. So, its not THERE. (That would be too easy, huh?) Adding to the fun is that the car was parked by the owner, and when he returned, the problem had surfaced.

Via Google I have seen the F21 circuit causing a variety pack of issues depending on where the fault actually is. I just have not been able to find a diagram that hints at where the potential cause may be. So, today or tomorrow I will be physically digging into harnesses and the fuse box.

In the meantime the radio, overhead monitor panel, instrument cluster, and various fuses have been pulled to isolate the problem. No help !! Where the short is it's a good one!! After all, it has popped more than one 10 amp fuse at F21. Next is trying to actually find S211 and start looking for the short with a multimeter.

[Andy Mechnic]

A true short huh? A short can be to power or ground, short basically means that the electricity is taking a path not originally designed into the circuit. I'm not terribly surprised that it's blowing a 10A fuse since the turn sigs run on a 15A circuit. Look for chaffed wires and shielding. Remember that the short can be internal in a connector as well.

[snaponbob]

The reason I said what I said about "shorts", is that constantly hear people talk about a short in their car because something is not working, only to (quickly) find that a failed component or an OPEN circuit exists. I was not making light of your comment. As for amperage, the first fuse I pulled out of the F21 location was a 15 amp unit.

This may become a PIA !!!!! But, won't be the first old car puzzle I have attacked.

[Andy Mechnic]

Wiring problems can be such a pain. Sounds like you have a fun weekend ahead of you. I hope you find it.

[snaponbob]

Just got better ..... or WORSE. Stepped into the shop, inserted f21, and ........ NOTHING.

This has already happened, and the the symptom pops up again. Coolness !!!!

[Andy Mechnic]

Gotta love it. Did something get wet maybe to cause the ""short""

[StereoInstaller1]

A fairly common failure on early cars is the domelight wires getting broken.

The 3 wires that run up the "B" pillar, generally on the right side, sort of under the back seat, sort of under the rear side panel. There is one of those tiny metal clips that hold the wires in place, seems to break there fairly often.

I've seen this issue on a half-dozen early cars, have yet to see it on a late model.

HTH, best of luck.

Oh, you can buy little circuit breakers shaped like an ATC fuse, use those so you don't chew through 20 fuses until you find it. I keep a half dozen in my toolbox, they really help.