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MG MGB Technical - Backup lights not working...
|Noticed that my backup lights on my '79 "B" do not function. Where do I start to find the source of the problem? What the most common cause? |
It's quite a simple circuit, first check the bulbs and rear wiring, then the connectors near the bulkhead, then the reverse light switch, which is a pain to get at (under the transmission tunnel).
Has your car suffered wiring damage due to the overdrive wire shorting ?, this could cause probs with the reverse light feed, which is in the same loom limb.
|If you haven't looked yet check the connectors to the lights. I knock mine off whenever I put something big in the trunk (in this case squeezing in my hockey bag).|
|Just a practical hint: Start at the light socket itself with a voltmeter. Work your way forward, at each connector check again. Clean connectors as you go for the future. If you get to the switch and there's no voltage before that, you could add a wire if necessary. It can take a lot of time, or it can be simple. You did replace the bulbs and clean the sockets?|
|You have got good advice, just remember to check the earth as well. A wire from the socket to a good ground will sometimes result in illumination.|
|I had both lights out so I was convinced it was a switch or supply problem. Spent ages under the car tracing it through - turned out both bulbs had gone!|
|Thanks for the tips. I know the bulbs are fine. Don, you mention something about an Overdrive short. Funny, but my car has an Overdrive and it doesn't function. Maybe, you're on to something. Where should I look if I do have an Overdrive short?|
There is a wire that goes from the bulkhead to the overdrive switch in the gearknob. The insulation on the wire tends to chafe through near the knob, which results in a short circuit to earth in the unfused wire.
This results in damage to that section of the wiring loom, which includes the wire to and from the reverse light switch.
This thread was discussed between 28/07/2005 and 30/07/2005
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