The infamous fuse 21 problem

[sheldpaugh]

Buying a 1988 320i tomorrow and it has an electrical problem. Radio, tach, obc all don't work, you know the typical fuse 21 problem. Anyway, he's already tried changing the fuse, it just pops as soon as he puts it in. He says he's searched the typical areas for shorts except for behind the radio which is the factory one I believe. Anyone have this problem and know possible fixes? Could the SI board cause this? Thanks

[M3and2002]

The infamous fuse 21 problem

I just went through this with my son's 86 325es. Mine turned out to be the reverse switch in the trans had shorted out by getting oil in it. Just pull the shifter boot up and there is a connector with the two wire going into the rubber sealing boot, disconnect the connector. Replace the fuse and all should be good. If that works replace the reverse (back up light) switch and reconnect the connector above.

[sheldpaugh]

I just went through this with my son's 86 325es. Mine turned out to be the reverse switch in the trans had shorted out by getting oil in it. Just pull the shifter boot up and there is a connector with the two wire going into the rubber sealing boot, disconnect the connector. Replace the fuse and all should be good. If that works replace the reverse (back up light) switch and reconnect the connector above.

Where is the switch located? And is this what you are talking about? Post #8

http://www.e30tech.com/forum/showthread.php?t=98184

[2002jm]

yes

Had the same problem with my h26. When you pull the shift boot out, you will see the wiring harness. If it touches to metal, you will lose the fuse:)
jm

[sheldpaugh]

Had the same problem with my h26. When you pull the shift boot out, you will see the wiring harness. If it touches to metal, you will lose the fuse:)
jm

Glad to see that this is such a common cause for it, don't know if the owner checked there yet but I'll check again once I get it

[2002jm]

yes

It is a direct short, if the wires are touching. So every time you turn on the key the fuse will blow:). Makes it sort-of hard to check to see what is happening. Mine did not look too bad, but the wires were pressed against the body and that is all it took to short. pretty easy to rewire.
jm

[sheldpaugh]

It is a direct short, if the wires are touching. So every time you turn on the key the fuse will blow:). Makes it sort-of hard to check to see what is happening. Mine did not look too bad, but the wires were pressed against the body and that is all it took to short. pretty easy to rewire.
jm

Thanks for the help! Also, did you have battery drain problems because of this?

[KyleDriver]

had the same exact problem in my '87, as soon as I would put the car in reverse fuse 21 would blow. everyone that posted here is spot on, my reverse switch wires were frayed and contacting the chassis causing a short. I repaired the wiring, problem went away immediately.

good luck.

[sheldpaugh]

**UPDATE**

Got the car today, buddy only checked the wires by the drivers door, will check under shift boot tomorrow!

[flyboyx]

good luck man

[sheldpaugh]

**UPDATE (again lol)**

Disconnected the connector under the shift boot, everything works fine with it disconnected, fuse didn't blow. Thanks everyone for the help, if I could buy you all a beer I would!

[sheldpaugh]

had the same exact problem in my '87, as soon as I would put the car in reverse fuse 21 would blow. everyone that posted here is spot on, my reverse switch wires were frayed and contacting the chassis causing a short. I repaired the wiring, problem went away immediately.

good luck.

So is it the wire coming out of the rubber hole or a wire that's on the connectors?

[f4tj0n]

So is it the wire coming out of the rubber hole or a wire that's on the connectors?

Same wire.

[sheldpaugh]

Same wire.

Realized that after I tugged on it hahah

[2002jm]

yep

Had the exact same problem and disconnecting the wiring harness under the boot did the trick. I will go back soon and fix the wires:)
jm