No Back-Up Lights

[Foster48x]

I cant seem to get the back-up lights to work on my 80 FI. Every time the transmission goes into reverse the "A" fuse blows. All of the other lights work and I'm pretty sure I got all of the grounding issues on the tail light circuit boards fixed (maybe not).

Where would you guys look first? Another grounding issue on the board or the actual reverse light switch? Maybe someone can answer this also, the switch is located on the passenger side of the trans facing the rear with two black wires coming out of it, right? The two black wires are connected to a plug with one white wire and two lt blue/white wires (these 3 go up into the wiring harness). The reason I'm asking is the wiring diagram shows one less lt blue/white wire going into the harness (only 2). The white goes all the way to the left rear circuit board (I tested it and its hot). The lt blue/white goes to a delay switch and then to the gas sensor? Why the gas sensor? Should I be looking for a possible ground issue up in the dash?

Rick

[mbouse]

rick,
electrical circuits need to be looked at one step at a time; process of elimination style. since the fuse blows whenever you go into reverse gear, i'd start with the switch on the transmission.

of course, you have cleaned the bulb sockets and assured that the bulbs are good, and the wiring to the bulb sockets are clean and not shorting out.

you know where that tranny switch is... disconnect the wires from that switch. does the fuse still pop? if not, short the wires together. does the fuse pop, or do the lights come on? if the lights come on, then the tranny switch is toast. if the fuse pops, the answer is prolly not the tranny switch, it is prolly the wire(s) shorting out somewhere up the line...or as you indicate another component. follow the wires upstream until you are certain they are not shorting out somewhere.

my bet is the tranny switch or the wires to the switch are shorting out when you select reverse

[Foster48x]

Mike,
Wwhen the wires are diconnected from the reverse switch the fuse is ok. What two wires should I short? The switch has two black wires coming off of it but where it plugs into the wiring harness there are 3 wires (2 lt blue/white and one solid white). It doesn't match the wiring diagram. Should I short the 2 lt blue/white and the solid white?

Thanks for the reply.
Rick

[mbouse]

i like breaking the circuits down to their smallest components. process of elimination.

First take the two black wires that should connect to the switch and short them together. if the fuse does not blow and the lights come on, then i would suspect the switch is faulty. if the fuse blows, then the trouble is prolly not with the switch, it is prolly upstream somewhere with the wires.

i always suspect after-factory wiring jobs... but, that does not mean that your wiring diagram should match. unfortunately, Luigi at the factory was known to use whatever wiring laid around when he ran out of "the right color".

can you see 100% of the wires before they disappear into the loom? if so, do they look good, or is one shorted to the body?

[Foster48x]

As far as I can tell the wires look good up to the wiring loom. I'm going to try shorting the black wires off of the switch first like you suggested to see what happens. Thanks for pointing me in the right direction.

I think the cost of 8a fuses is beginning to surpass the cars net worth
Rick

[Foster48x]

Got it!
Switch was good. I was able to trace it back to a bad ground on the rr tail light board that I thought was fixed. I'm just happy it wasn't up in the wiring loom. We'll I'm one more project closer to actually getting to drive it .

Thanks again for your help Mike.
Rick

[mbouse]

glad you found it outside the loom.