1987 blowing tail light fuse

[theokengineer]

My 1987 accord LX with manual transmission and 292K miles on it has started blowing the back up light fuse when I shift into reverse. It doesn't do this when I am going forward (all gears). All of the tail light and back up bulbs are good, and I have even disconnected the back up lights and the fuse still blows. Sometimes I get the tail light warning light on the dash, but usually that doesn't come on.

It may be a coincidence but on the highway I started losing power the other day (a couple of weeks after the fuse stared blowing), got off and had a leak in a hose. After I fixed it the oil light has started to come on, again only if I put the car in reverse. After the oil light comes on I can then turn the car off and restart it and light won't be on or come back on unless I put it in reverse (oil light is on if I change the blown fuse). I changed the oil sending unit with no change and the engine isn't over heating. The oil pump is brand new so I think the oil light is an electrical problem, probably related to the back up light fuse blowing. Could it be a bad ground somewhere?

Any help would be appreciated. I have taken my instrument panel off and checked the wire bundles behind it and under the dash, but don't see a chaffed wire or shorted wire.

[rc00netzero]

The involvment of the oil pressure light is a puzzle - but the behavior of the backup light says you have a short to ground either in the switch on the trans or in the wire between the switch and the lights in the rear of the car. It is a pretty simple circuit. If it were mine - I would start with the switch end, and work to the rear. The added oil pressure light behavior MIGHT be caused by the wires running in the same harness at some point.

[theokengineer]

The back up switch doesn't run very far until it combines with a large wiring harness that then runs up in front of the battery and disappears behind the fender (I believe). So digging into it looks painful. Is there a way to take the back up switch off and test it or test it on the car? I would like to take your advice and start there.

[HLW]

The back up switch doesn't run very far until it combines with a large wiring harness that then runs up in front of the battery and disappears behind the fender (I believe). So digging into it looks painful. Is there a way to take the back up switch off and test it or test it on the car? I would like to take your advice and start there.

Before the wires get to the harness, there is a plug for each wire. This is there so you can easily replace the switch. You can disconnect the plugs and test the stitch on the car by checking for a short across the wires form the switch with the tranny in reverse and no connection between the wires when the tranny is not in reverse.

You can also test the wires going to the harness (loom). One should short to ground and the other should have power when the ignition is on and the trany is in reverse.

The backup light gets power form the same circuit as the gauges and warning lights on the instrument cluster. You should check everything on the circuit because it might have more load on it than it should and the backup lights could just be adding enough load to blow the fuse without the issue begin in the backup lights and associated wiring.

[lostforawhile]

the back up light switch isn't a grounding switch, it switches hot, unlike most of the other circuits in the car

[HLW]

the back up light switch isn't a grounding switch, it switches hot, unlike most of the other circuits in the car

Yes it does, that just means that the side that will read as a short to ground will read a high resistance and still be 0V and the other will be 12V when the ignition is on and you re testing the wires with the switch disconnected. I was at work trying to remember the wiring without the diagram in front of me. It also means that if there is a low resistance that remains with the backup lights disconnected, it will still have a short to ground if the wire between the switch and teh lights is shorted to ground.