Back-up light

[dfwcantor]

THe c/s backup light on my '02 Marathon XL didn't work. I removed it, and hooked it directly to a battery and it lit up. I concluded the connections were bad, re-installed it and still doesn't work. Anyone know if there is a dedicated fuse to the c/s backup light? Can't see a problem with the wiring connections close to the light. Ideas?

[gmcbuffalo]

I don't understand the symbols

C/S ??

[Gil_J]

If c/s is curb side and the fixture is good then there's only wire and the connector behind the tail light assembly that can be bad. I'd first see if voltage is making it to the connector. On mine, that would be wire number 32. Again, I'm assuming only the curb side is not working.

[dfwcantor]

c/s = co-pilot side = curb side = passenger side. We should probably just use "port" and "starboard" like the boat people.

[dfwcantor]

Any tricks for checking current on a backup light? The other one goes on only with 1) the engine running, and 2) the transmission in reverse. I trust my parking brake and my chocks but not sure I trust them enough to be kneeling behind the bus with a multimeter fiddling in the engine bay with the engine running...

[Gil_J]

Yes, engine has to be running.

Just to be sure, what did you remove and connect to the battery (bulb or light module)? If just the bulb, you can check voltage inside the module between the black wire terminal and, if like mine, either of the 2 yellow wire terminals. If you don't have the 7 stacked light modules, then I'm not sure how it's wired.

[gmcbuffalo]

follow the wire from the fixture to the source terminal you may have a broken wire or a short somewhere.

[dfwcantor]

The fixture is a housing with an H3 halogen bulb in it with just 2 wires, white and black. I removed the entire fixture and connected it to a freestanding 12v car battery I had at home and it lights up as bright as you would expect. Cleaned the connectors up and reinstalled it and still no function. Following the wires up stream they disappear into a bundle of wires all encased in conduit and secured with multiple band ties. I didn't want to take that all down to go fishing. Couldn't find any obvious loose connections or anything. It's going to Marathon in Oregon later this summer so I guess I'll let them figure it out. ($$$Ouch!)

[Gil_J]

If you really want it working now and don't want to dig into the wiring harness, here's the easy method.

First, check to see if you have voltage on either wire going to the light. Make sure your voltmeter is connected to a good ground and not the other wire going to the light. If you discover voltage then the other conductor is the ground conductor and it has an open. If you don't discover voltage then turn off the backup lights and look for 0 ohms between one of the conductors and the same ground. This will identify which conductor is ground.

Second, now you have determined that one conductor either has voltage or is the ground wire. If the ground was open simply add another wire from the ground conductor to a known good ground. If you didn't find voltage you need to first make sure that each back-up light isn't protected by individual circuit breakers as is the case with the left and right brake lights on my XL. You can go to http://prevostparts.volvo.com/techni.../en/wiring.asp to check your wiring diagram. You may also have a description of your breakers inside one of the engine bay doors. If you've ruled out a circuit breaker, cut the voltage wire near the backup light in place that can be easily repaired later. On the side of the cut leading to the back-up light run a wire from that point to the functioning back-up light. They have crimp on wire taps that will allow you to connect to the good back-up lights voltage wire without cutting it. Secure the new wire. Protect the other side of the wire that was cut with a crimp connector or electrical tape.

You now have a functioning back-up light.

[gmcbuffalo]

I would think the Prevost part of the wire (the wire going to the interior and disappearing) should have a number on it. If you go to the link GilJ gave you you should be able to trace the wire on the drawing and see where it's junctions are located. Those junction should be accessible, find those and do what Gil told you to do find voltage. The junction that has no voltage from the last good junction will be the shorted or broken wire. I think the two back up light come off the same CB so if you have a short I think it would be tripping the CB. Since it is not you have a broken wire. From the wiring diagram you should be able to determine where the wire from the CB splits to each light.