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1967 - 1972 F-100 & Larger F-Series Trucks Discuss the Bumpsides Ford Truck

Electrical gremlin help

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Old Jul 1, 2020 | 09:53 PM
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Restenhaus72's Avatar
Restenhaus72
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Electrical gremlin help

recently acquired a '72 F100 (302 w/C4 tranny). The truck came pretty well sorted electrically (everything seems to work). I did notice though that my back up lights remain on in all gears.
Any suggestions on where to start first ?
Thanks !
 
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Old Jul 1, 2020 | 10:46 PM
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Originally Posted by Restenhaus72
recently acquired a '72 F100 (302 w/C4 tranny). The truck came pretty well sorted electrically (everything seems to work). I did notice though that my back up lights remain on in all gears.
Any suggestions on where to start first ?
Thanks !
I would do the simplest thing first - unplug the connector going to the backup switch on the transmission and see if the lights go out. Then test the switch for continuity in all gears. If the lights turn off when you unplug the connector then it's probably the switch; that's confirmed by testing the switch itself. It should only be closed (i.e. you should only have continuity) when in reverse. If the lights stay on, then you'll be looking for a short elsewhere in the harness.

I should note that I'm saying this based only on experience working with the switch on a T18, though I am assuming that the same basic type of switch is used on the autos; I am reasonably sure that the wiring is all the same otherwise.

Good luck!
 
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Old Jul 2, 2020 | 08:21 AM
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Sparky72, thanks for the response. Can anyone else verify if the back up switch on the C4 is located on the transmission ?
Thanks !
 
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Old Jul 2, 2020 | 10:47 AM
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sparky72
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I did a little more reading this morning and it looks like the backup switch is actually built into the neutral safety switch, which is attached to the steering column near the base (by the firewall). I don't have any experience working with those auto switches so I will leave that to someone more knowledgeable than me.
 
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Old Jul 2, 2020 | 08:41 PM
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Testing is done the same way be it the switch on the transmission or down on the column.
Dave ----
 
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