Interior lights always on

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Jun 13, 2011 | 11:18 PM

snakedoc

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From: AL, Reform

Interior lights always on

My brother has a 1979 Ford F-150 that the interior lights (dome, under dash, and cab) always stay on. Have seen many post about lights not working, but none that address them not cutting off. One door switch was broken and preventing it from switching off, but it has been replaced and they still stay on. Twisting the headlight switch will not cut it off either, but will dim the dash lights. Also, pressing either door switch will cause the lights to flicker, but they remain on. Is it most likely the headlight switch or is there something else that he should be checking? It would be nice to not have to undo the battery or remove the bulbs to it from draining the battery.

Jun 14, 2011 | 07:37 AM

fmc400

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From: Austin, TX

Try unplugging both door jamb switches with the dimmer switch in the OFF position (where the dome light would normally be off with the doors closed), and see if the lights go out. If you have a cab light (on the outside), you should also have a switch behind your head - try unplugging that next. If they still stay on, try unplugging the headlight switch and see if they go out. When you work with the headlight switch, you should disconnect the negative battery cable, then unplug the headlight switch, then reconnect the battery cable. There's heavy-gauge hot-at-all times that runs to the headlight switch, and it's easy to ground out.

Whichever switch makes them go out would be the one I'd suspect to have an internal short.

Jun 14, 2011 | 07:41 AM

Paul49

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My truck is a '75 - and may be different. It only has three possible sources to feed the dome lights, and they are the headlight switch and the two door jamb switches. The dome light is grounded at the light fixture, and must get power from some source. I would try the easiest first and that would be the two door jamb switches. They are easily removed and have a plug on the back that will disable them completely. And they are cheap to replace if they come apart in the removal. If the light still burns, you have narrowed it down to the headlight switch. . .

Unless - there's something really wierd that's happened to his wiring. Maybe someone has added something recently? If that's the case, then I'd look over the added item to see if it could be the culprit.

Good luck with your search,
Paul

Jun 14, 2011 | 07:44 AM

Paul49

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Quote:

Originally Posted by fmc400

Try unplugging both door jamb switches with the dimmer switch in the OFF position (where the dome light would normally be off with the doors closed), and see if the lights go out. If they still stay on, try unplugging the headlight switch and see if they go out. When you work with the headlight switch, you should disconnect the negative battery cable, then unplug the headlight switch, then reconnect the battery cable. There's heavy-gauge hot-at-all times that runs to the headlight switch, and it's easy to ground out.

Whichever switch makes them go out would be the one I'd suspect to have an internal short.

Sorry FMC400 - we said the same thing, but you type faster. . .

Paul

Jun 14, 2011 | 08:15 AM

mark a.

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If you have a outside cargo light the switch may be on inside the cab & the inside lights will stay on.

Jun 14, 2011 | 10:31 PM