back up lights - Vintage Mustang Forums

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post #1 of 10 (permalink) Old 11-18-2012, 02:21 PM Thread Starter
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back up lights

Here's a new one for me. On the '66 coupe I recently acquired, the backup lights come on whenever the ignition is on. Some previous owner has gotten some wire crossed. Anybody have a cure? Thanks..
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post #2 of 10 (permalink) Old 11-18-2012, 04:07 PM
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Have you checked to see if the backup light switch is shorted? It is 'NO" (Normally open) meaning that you will not have continuity across the terminals when it is in the OFF position. If that's working okay then check the wires to and from the switch to see if they are bare and touching anywhere.


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post #3 of 10 (permalink) Old 11-18-2012, 05:23 PM
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Is it a manual or automatic?

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post #4 of 10 (permalink) Old 11-18-2012, 05:44 PM
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Make sure the po didnt put a toggle switch somewhere to run the lights, and someone may have bumped or left on. I have seen it happen.

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post #5 of 10 (permalink) Old 11-18-2012, 10:10 PM Thread Starter
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Should've mentioned it's a C4 auto with a 289.
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post #6 of 10 (permalink) Old 12-11-2012, 05:22 PM Thread Starter
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follow up

I finally got around to unplugging both sets of for the neutral safety switch, the other for the backup lights....and STILL the backup lights stay on when the ignition is on. Thoughts about troubleshooting this?
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post #7 of 10 (permalink) Old 12-11-2012, 10:03 PM
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The 1966 wiring diagram shows a black / red tracer wire traveling from the fuse box to the back up lamp switch on the transmission selector shift shaft. Since the backup lamps illuminate even with the wiring disconnected at the backup lamp switch on the transmission, trace this black / red wire to the backup lamps and determine if there is a splice with an added wire.
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post #8 of 10 (permalink) Old 12-11-2012, 10:42 PM
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Pull the fuses one at a time until you find the cricuit that is providing power to the lights. That's the first step. Once you find the circuit at fault, you will probably have to do a "hand-over-hand" inspection of the entire wiring harness to find out where the problem is. I would start at the backup lights and work my way forward. When tracing the wiring, I would keep a close eye out for any splices or those crappy Scotch-lock wire taps that people use when trying to wire up a radio - most of the time those end up being the problem. A previous owner may have tapped into that wire thinking that it was a good power supply and then ended up back-feeding it from another circuit that has power when the key is on.

The wiring in my car was so butchered that I ended up throwing it all out. Before I bought the car, a friend of mine owned it. If the headlights were on and you turned the ignition off, the car would stay running until you turned the headlights off. The wiring was spliced and respliced so many times that it was barely recognizable.

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post #9 of 10 (permalink) Old 12-12-2012, 11:13 PM Thread Starter
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No wonder the previous owner's "solution" was to unplug both lights at the trunk connection!!
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post #10 of 10 (permalink) Old 12-13-2012, 10:25 AM
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I would work back from the light and see where it goes. If you disconnect the switch and it is still on, it is shorted to something else.
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