Fuse #27 reversing light 10 amp fuse keeps blowing

[Halftim3]

Like the title says, the #27 reversing light 10amp fuse keeps blowing and I believe its the cause for slowly draining my battery overnight while the car sits. I have to jump the car to get it to start if it sits long enough.
It only blows the fuse when I put the gear into reverse. If in ignition position 2 in neutral the fuse does not blow.
I have replaced the back up light switch with an FAE brand part number 23147524811 and I have replaced with new reverse light bulbs 1156 and cleaned the contacts and still blows the fuse once put into reverse gear. I checked the wiring in the rubber hoses that goes into the trunk from the body on the passenger side and could not see any broken wires from the small space I could see.
My car is stock with the business CD unit with no aftermarket stereo.
If anyone has ideas, please let me know. Thanks.

[sapote]

It only blows the fuse when I put the gear into reverse.

This means you don't know if the light turned on or not during reverse?
We need to know 6mt or smg, male/female, and built year/month, especially for troubleshooting electrical circuit.

[Halftim3]

I believe the reverse light does not turn on when this happens because the fuse blows as soon as it is put into reverse gear with key in ignition and in position 2.

It is MY 2004, build date 11/03. Original 6 speed transmission, not a swap.

[Estoril]

I you put a meter on the light connector and tested for a short?

[Halftim3]

No, but I do have a meter, but I'm not sure how to test for a short. If you walk me through, I can try.
I dont know where to set the knob on the meter and it has a positive and negative wire/cable. Do I unplug the reverse light connector and insert/poke positive and negative wire to each side of the connector? I still don't know where to set the knob.

Thanks.

[sapote]

The reverse switch connected to a few things beside the reverse light bulbs: mirror motor controller, PDC, Navigation computer, and the instrument cluster.

All of them connected to X428 connector behind Glove Box, so you might need to disconnect each of them from X428 until no more short circuit.

To find the short without burning many F27 fuses: remove F27 and with the voltmeter find out which pin of the fuse socket has 12v with key turned to ON, then the other pin (let's call it R pin) is the one we're interested as it connected to the reverse switch.

Now with gear shifted to R, check if R pin is shorted to ground (measure resistance from R pin to GND. If yes, then start remove each wire from X428 until no more short and identify the wire color that causing the short and we will work from here. (Key might not need to turn On during these step.)

[L0okitzRaj]

If nothing else works, I would recheck the trunk harness. It happened on a previous e46, and it was really hard to see the short without pulling the whole harness out of the sleeve, and trunk. I'd make sure to use some fishing line to help make threading hte harness through the trunk easier.

[Halftim3]

I see a problem, how does that happen?

[Estoril]

Whoa. Is that simply corroded - or corroded and some strands melted?

[Halftim3]

I think corrosion and some strands melted. Look at the color of the terminal connector, it's copper so maybe it got hot? Battery was probably being undercharged due to the corrosion? My replacement negative battery cable terminal connector is silver. Would anyone check theirs just to make sure? I hope this solves my battery draining. Also Fuse 27 has not blown since.

[Halftim3]

Looks like one strand melted in this photo

[Estoril]

You may have melted a strand or few due to the heavy corrosion and the resistance that it caused. Any melting of the sheath?

I'd do the splice a good distance from any obvious discoloration. Make it a great electrical/mechanical splice.

[sapote]

Like the title says, the #27 reversing light 10amp fuse keeps blowing and I believe its the cause for slowly draining my battery overnight while the car sits. I have to jump the car to get it to start if it sits long enough..

A badly corroded battery negative cable can explain part of these problem but not all.
* It is why you needed to jump the car to start it as the battery could not deliver enough current to the starter.
* It was not the cause for F27 blown.

Why cable corroded? Previous battery leaked via the negative post and the acid got to the cable crimped terminal and corroded the copper wire.