[adamg69]

Where to start looking?? All the electrics (apart from this) on the car work. I tested that there was 12V on one pole of the connector for the backup switch on the firewall harness and connected it directly to the other pole of the connector, shouldn't I now have 12V back in the trunk connectors of the back-up lamps?? (This is on a 69, the harness connector I am talking about is the 4-pole or pin one where the other two poles are jumpered - neutral safety switch - I have a toploader). Anyway, the back-up lamps didn't come on and there was no 12V on either of the connectors back there. Everything else on the harness works. I did this with the key in the ignition position and like I said before, at least one side of the firewall harness connector had 12V as expected. I am stumped...

69 fastback, 351C, 4spd toploader, restomod BOSS 429 clone

 

[Midlife]

I had this problem with backup lights and my 4-speed switch. The damn wire had 12V into the taillight when I unplugged it, and when I plugged it in, I got no lights. It turns out that if the connection is just barely there, like just touching loosely, the current draws down the voltage to nothing, and nothing comes on. It took a lot of effort to track that answer down.

Try back at the Neutral Safety Switch, and ensure that the switch is securely installed, engaged, etc. Track all connections back from there, and you should get lights. If not, check the bulb housings for possible shorts.

Let me check your shorts! My multimeter is just a-waiting!
King of the Old VMF with >5000 posts, so ignore the titles here...I'm really THE Old Fart *LOL*