Fuse 10 Issue

Post Mon Jun 22, 2020 1:43 pm

Well, June seems to be a fun one for little issues cropping up.

Fuse 10 keeps blowing when I put the car in reverse...the engine fan is linked to it along with the interior fans and tach/fuel and temp gauges.

I removed the wires that lead to the switch on the gearbox and there was what appears to be a short that I taped up to test. There doesnt' seem to be continuity between the two different wires so unsure if that's the issue (the fuse keeps blowing when I tested that).

In my mine it seems most likely the short is in the gearbox switch or the reverse bulbs themselves (which are a PITA to get out due to rusted screws it seems). Any ideas on what is the most common issue here? Internet research seems inconlusive for now.

Cheers,
Gus

Post Tue Jun 23, 2020 5:40 pm

Based on the map I have for the backup lights, when you put the car in reverse, it closes the gearbox switch. So the two wires are therefore connected to each other. Then, it goes directly to the bulbs.

If I were you, and especially because it blows when you put in reverse, I'd look into the bulbs and their mounting plate.

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Post Tue Jun 23, 2020 5:42 pm

BTW Fuse 10 does not seem to be linked to any fan? Yet, it is tied with the instrument cluster. Assuming you also have a 325i.

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Post Tue Jun 23, 2020 6:16 pm

I am guessing it's something to do with the M52 swap - potentially something to do with the temperature gauge input to turn the fan on when the coolant temp goes off? 325i Sport is the factory body loom at least

Post Tue Jun 23, 2020 6:44 pm

If the fuse only blows when you put the car in reverse, then what makes you think it's anything to do with the M52 swap?? The most common cause of fuse 10 blowing, by far, is the wiring from the gear lever grommet to the gearbox switch underneath the car perishing (it's rubber) and shorting to metalwork, or the wiring coming loose and getting involved with the moving gear linkage or the prop shaft.
The short can also be anywhere in the wire from the plug by the base of the gear lever to the reverse lights at the back of the car, but there are no known weak points there, other than damage from welding sills or rear arches.

Post Tue Jun 23, 2020 6:50 pm

The M52 swap - meaning the reason the engine fan is connected to that fuse.

I've got the wiring out and it seems mostly intact but will re-heatshrink and see if that helps. It was crushed a little to the centre console. I'm replacing the reverse switch in the box as a precaution since they are fairly cheap.

The rear arches have been done at some stage, but it wasn't an issue till very recently when I had the exhaust done. Will report back once the new wiring is installed - may need to re-read the Bentley about how to test for short circuits. Not my forte.

Then I can get on to the indicator issue where it keeps having intermittant flashing issues (like when a bulb goes)...fun & games

Post Tue Jun 23, 2020 6:52 pm

Does the fuse blow ONLY when in reverse?

Post Tue Jun 23, 2020 7:21 pm

From what I can tell, yes - it was running for 1-2h on Sunday after replacing the fuse....as soon as reverse needed, gone. I've re-taped some of the wiring that looked less than ideal on the wiring that runs along the shifter, stripped all the heatshrink off and checked for contact and re-tested - and it still blows.

Post Tue Jun 23, 2020 9:05 pm

In that case, what I wrote above stands. It cannot be anything to do with electric fans or anything else to do with the M52 installation.
Carefully pull the plug and socket for the reverse light wiring at the base of the gear lever apart, without disturbing things as much as possible, and see if the fuse still blows.

Post Tue Jun 23, 2020 10:01 pm

The fuse doesn't blow with that unplugged - so I'm figuring the issue is at the switch or the bulb end?

Post Tue Jun 23, 2020 10:23 pm

Suggests the opposite to me - that the fault is in the wiring under the car. Try just connecting the green/white at the plug and socket, leaving the blue/white still disconnected. You may have to use a piece of wire to do this.

Post Tue Jul 14, 2020 11:14 am

To report back - it was exactly as Brian said, the wiring from the reverse switch to the main loom. There was a split in the wiring coming out of the plug that attaches to the reverse switch that must have been hitting the transmission tunnel and shorting...and my attempts to remove the pins from the plug to fix were...inconclusive.

In my defence (ahem), I had thought I had fixed it, but the ZF gearbox is a bit bigger than the Getrag, and the wiring pushes up against the transmission tunnel firmly...so obviously the short was going through my "repair". The wiring was brittle, so new E30 and E36 loom spliced together...I have reverse lights again.

Thank you!