No Reverse Lights

[deloryan]

My reverse lights aren't working on my 5-speed. Tested transmission switch and it was bad so I've replaced that. Now I'm getting voltage at the tail light board, but lose voltage when bulbs are inserted. Anyone seen this before? Seems like it should be working.


https://youtu.be/2wMBmUjV2cs

[Michael]

Just to eliminate any possibilities, I would insert all the bulbs in the sockets and see where you stand.

[DMC-Ron]

Ryan,
You're right. That is odd that the voltage disappears when the bulb is inserted. It looks like you have Grady taillight boards and they normally have reasonable quality sockets and good circuit traces. It would appear there is something resistive in the circuit and the bulb is pulling the +12 down to ground without getting the required amps to light. Here are some things to try:

If both left and right boards do the same thing, suspect the wiring ahead of the taillight board and go to item 2.

1. With your meter check the voltage at the taillight connector. The idea is to see if the backup circuit (green with brown stripe wire) +12 volts is pulled to zero.
2. If the +12 gets pulled to zero with your positive probe on the (green with brown trace) wire side of the connector, that tells you that the resistance is somewhere in the brake-light circuit coming to the board, not the board itself. Best check that new backup switch and/or the power to it.
3. If the voltage stays at 11+ volts at the connector, then there's something on the board at issue. Since the bulb works in the other socket it seems likely the ground connection is OK which means the +12 voltage is not making it to the socket.
4. Use your positive probe to trace the circuit from the car connector to the bulb connection. A likely suspect would be the metal contact in the car connector is not griping the board contact. It will pass the voltage when there is no load but as soon as the bulb is inserted it won't pass the current. It might also be the socket itself.

Good Luck, Ron






Taillight connector pinout.jpg

[Ron]

Also check for poor connection(s) at Red Bulkhead connector.

[deloryan]

Here’s the culprit. The green/white wire can pass voltage but no load. This is the wire from behind the engine down to the reverse switch. It was kind of kinked up with zip ties so maybe that explains it.

[TheStoot]

yea same happened to me. My switch was fine but the wiring got melted along the exhaust crossover pipe somewhere underneath. Ran a new wire and all was happy again!