When I was getting my car inspected last year, they noticed my back up lights weren't working. (After they put the sticker on my car) Yesterday when LarryW and I were working on my carb problem I noticed that one of the wires from the switch wasn't connected. I fixed that, but how do you test these? I used a meter and could not find any voltage going to or from the switch with the key in the on not start position. Does anyone have some tips on troubleshooting this circuit?

Thanks

George

From the wiring diagrams the ignition switch needs to be in the "run" position. If you have a voltmeter you can check continuity through the switch using the ohms scale. With no power on the switch, put the car in reverse and see if you have 0 ohms across the contacts which indicate the switch is closed. If you have continuity then make sure you have 12v to the switch by measuring between the terminal and ground. If you have continuity both contacts will have power. If you have power to the switch and continuity through it, check the grounds and the light sockets.

George,

I strongly suspect your problem is pretty simple to solve.

In my car (Jan,'72 build), I do not even need a key to test the back-up lights. My lights are on a constant hot. No keys needed. That's why we can forget and leave lights on and return to a dead battery.

But to get power to the back-up switch, I do need to flip my light switch on - just parking lights will suffice. Why design a car to have back-up lights go on when the rest of the lights are off? Then to have the lights turn on, the car needs to be in reverse so the switch can be closed.

See if this does it for you.

Larry

If Husker is referring to SOBill's diagram, as below, it does appear key must be on. But that is not the case for my car, and I believe others have also found this to be true.

I'm emailing Bill to get his thoughts on this diagram.

quote:

I do not even need a key to test the back-up lights. My lights are on a constant hot. No keys needed. That's why we can forget and leave lights on and return to a dead battery.

That's why the back-up lights should be on a key. My '71 is on the key, as per the SOBill diagram.

quote:

Why design a car to have back-up lights go on when the rest of the lights are off?

So that they (the back-up lights) will act as a warning to others that you are intending to back up the car. Kind of like having the brake lights warning of your intention to slow down or stop the car.

John

Here's what Bill Taylor just sent me:

Larry,

I have a '74 (#6338). I used the big wiring diagram when I made the individual diagrams.

There are wiring differences between early and late cars and this is one of them.

Early cars also differ in the ballast resistor/ignition coil wiring and the radiator fan wiring.

Your backup lights are fed via Fuse #3 and are hot whenever the parking or headlights are on.

Have fun,

SOBill Taylor

Some of the 71s like mine only work with the running or headlights are on.

Mike

The way the early cars' back-up switch is wired, the back up lights do not work unless you have the park/headlights on. The power for the circuit is on fuse #3. I switched the wire on mine per the wiring on the later cars to fuse #12 to power the circuit with the key on and the gear in reverse.
The early wiring config is a safety hazard since your reverse lights do not go on unless you have your park/headlight switch on. We've redone three early cars here to the later config with power from Fuse 12.

Good Luck

quote:

The way the early cars' back-up switch is wired, the back up lights do not work unless you have the park/headlights on.

Just wondering if we could track this by serial numbers.

Mine is #1490, build date 5/71, and has the back-up lights wired to the key. This is how the car was delivered from the LM dealer.

Mike's is #1887 and is wired to the headlight switch.

Bayani,

When you say "early" cars, do you mean pushbutton or just pre L? Do you have any serial numbers and build dates?

John

The cars we made the corrections to are 71's &72's including a 72L. I have to check with Dennis to see if his Pushbutton was also off the headlight switch or not.

My #2645, build date 2/72. I'll see if I can gather the others we've done.

Note - My factory wiring diagram(dated 6/15/72) shows the back-up light circuit is powered off fuse#3.
It will be interesting to see what the earlier wiring diagrams show.