Fuse blows when putting in revers gear ?!

kehlerjonathan

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Feb 24, 2015
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Hi guys!

Little issue here with my 80s 4,2L 1992

I went for beach driving this weekend and washed the under body with high pressure water just after to remove sand and salt.

Since that, every time I put the reversing gear: A/C, ventilation and dashboard indicators ( speed, oil pressure, battery volt indicator and RPM ) fuse blows.

I changed the fuse many times and everything start working again until I put the rivers... it blows instantly...

I checked the reversing bulbes but they looks good.
I waited a few days to make sur everything is dry under after I washed it, still happening..

Any idea ?

I was thinking about the revers switch or relay, but no idea where it is.

Thanks for your help !
 

Julian T

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Dec 13, 2011
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Do you have a tow bar with electrics, might be worth checking the plug socket for water/corrosion if you do, I would start with the simple things first, you could disable the reverse lamp switch by unplugging it at the gearbox and checking if fuse still blows when you select reverse.

Oh and do introduce yourself to us here
 

clivehorridge

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Sounds like a short to earth somewhere on the reverse light circuit, the switch is on the gearbox, but the short could be anywhere.

Try to check all along the wiring loom from the switch to the lights, maybe the insulation is cut somewhere, usually where it passes through a chassis section, or at clips holding the loom to chassis.

If the spare wheel is slung underneath on the chain-lift, then it may have trapped the loom and cut it.
 

Dave 2000

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I like the tow bar wiring/faulty reverse light switch going to earth, have someone watch the reversing lights as you select reverse, does one light and not the other, it might point to the faulty side just before the fuse blows? Chafed insulation as mentioned. Just a thought, is your car automatic? If so then it may have a multifunction switch that is different from the normal manual switch, this means that current would be sent to the dashboard indicator as well, had the dash or gear selector assembly out lately?

regards

Dave
 
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Towpack

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That fuse looks to be 10amp rating. To blow that instantaneously there must be a full short to earth somewhere. The switch on the gearbox switches through a +12v supply. I've known switches like these go faulty and short the contacts to the earthed switch body so, as suggested, unplug it and see if the fuse still blows. If it doesn't it's on the load side of the wiring towards the bulbs and trailer socket. If you have a multimeter, measure the resistance between the load side of the wiring connector off the gearbox switch (the wire feeding to the rear lights) and earth. With the bulbs removed you should get an open circuit or 0 ohms. If there's still a reading try moving the wiring around, especially at connections and see if the reading alters or disappears until you locate the fault. Also do you have a reversing bleeper/sounder wired into the reversing light circuit? If you have try disconnecting that. Just another possibility. JMO
 

StarCruiser

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With the greatest respect, the reverse wiring doesn't go to the trailer socket. Sounds like either the switch fault or a trapped or chaffed wire as others have said. Much of the wiring runs internally, but passes through rubber grommets in the body. As said, check these areas for chafing especially if a grommet has been left out/dropped out and allowed the wiring loom to drop and become chaffed against the body. Alternately, and I am not sure if the wiring route here, has anything been put in the boot that has possibly damaged wiring, perhaps heavy, perhaps pushed against the sides?
 

clivehorridge

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To my knowledge and IIRC, the loom runs from the GB along the chassis rails and up into the body at one of the rear corners. It rizzling down outside, so there's no way I'm getting on all 4's to check, the OP can do that all by himself :lol:.

I still think it's trapped/chaffed/broken wiring somewhere along the way or as said, a faulty GB reversing light switch.

Hope it's something simple.
 

Towpack

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With the greatest respect, the reverse wiring doesn't go to the trailer socket.
If you have full towing electrics the reversing light wiring will 'go' to the trailer socket. On the old 7 pin sockets it should be pin 1 of the 12s socket. On the newer 13 pin sockets it should be pin 8. The socket(s) wiring will be either connected via a plug and play connecter fitted by the vehicle manufacturer or spliced into the existing loom at a convenient point. If the fault is on the wiring to the socket after the splice/connector or the socket itself the effect is the same. JMO
 

kehlerjonathan

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I am in australia
Feb 24, 2015
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With the greatest respect, the reverse wiring doesn't go to the trailer socket. Sounds like either the switch fault or a trapped or chaffed wire as others have said. Much of the wiring runs internally, but passes through rubber grommets in the body. As said, check these areas for chafing especially if a grommet has been left out/dropped out and allowed the wiring loom to drop and become chaffed against the body. Alternately, and I am not sure if the wiring route here, has anything been put in the boot that has possibly damaged wiring, perhaps heavy, perhaps pushed against the sides?
Hi Starcruiser, I removed the plastics side in the boot and verified the wirings and connections, everything is fine. I will disconnect that back light switch and check the trailer plug.
 
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