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Stumped: Reverse Lights Stay On

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Old 05-05-2018, 09:23 PM
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Stumped: Reverse Lights Stay On

Just wondering if someone could give me a hand / advice on how to proceed to troubleshoot this problem. The reverse / backup lights on my mustang (2011 3.7, M\T) stay on all the time. Doesn't matter what gear the car is in, the keys don't even need to be in the ignition the lights just stay on. I have to pull the negative terminal off the battery to shut them off. As soon as the battery is reconnected they turn back on.

My first thought was the reverse switch on the transmission. I disconnected the switch and have left it disconnected but no change the lights stay on. Nothing in the manual in either the passenger fuse panel or under the hood specifically calls out the rear lights, not sure what I would expect to find even if it did (since they are ON, not off).

I checked the sensor while it was disconnected (and the care in a forward gear) and the circuit it open.

I have done done a ton of searching online but canít anyone that has experienced the same problem.

Any suggestions?



Last edited by adblink; 05-05-2018 at 10:30 PM.
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Old 05-06-2018, 12:55 PM
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UPDATE ** (all of this testing was done with key off, forward gear and reverse switch on the transmission disconnected)

Looking at the prints Ford Workshop Service & Repair Manuals - 2011 Mustang 2011 Mustang 093 - reversing lamps. It shows the 2 wires coming out of the "body module b" going to the L & R reverse lights. I located the module and disconnected the larger black connector, the reverse lights turn off.

I manually powered the body control module only without the connector by running a jumper from the connector battery (-/+) to the body control module. Using a test light I found that the only 2 pins that had power still in this condition were the 2 pins for the L & R reverse tail lights. According to the drawings the (+) is always hot, and it doesn't mention the (-) so I'm assuming that isn't switch. To me it sounds like that module is the problem? Internal short that is sending power to those 2 pins all the time?

https://imgur.com/A9muZRW
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Old 05-11-2018, 07:44 PM
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Haven't made any progress, and despite lots of cross posting online can't find anyone who has experienced this.

Doing something I didn't think I'd ever have to. Taking it to the dealer this Wednesday.
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Old 05-11-2018, 11:39 PM
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Sorry no one was able to help. Let us know what they find.
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Old 11-01-2018, 09:12 PM
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Reverse lights

I am wondering if the back up lights are a "Ground seeking circuit" , in other words there is power to them all the time and they only come on when the gear selector is in "reverse" and the ground is provided by the selector. A rubbed wire somewhere could be completing the circuit on you when it is not in reverse. I'm betting this is a simple wiring snafu
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Old 11-01-2018, 09:30 PM
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Originally Posted by Mudlite View Post
I am wondering if the back up lights are a "Ground seeking circuit" , in other words there is power to them all the time and they only come on when the gear selector is in "reverse" and the ground is provided by the selector. A rubbed wire somewhere could be completing the circuit on you when it is not in reverse. I'm betting this is a simple wiring snafu
Is there any evidence of oil or cracks in the insulation on the wiring especially around pinch points? Oil will penetrate the insulation and create a circuit to ground either at a pinch point or through another conductor.

Have you replaced any lights with LED bulbs? LED Bulbs can play havoc with lights on ground seeking circuits because of the electronics powering the LED's

Last edited by 83convertible1001; 11-01-2018 at 09:49 PM.
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Old 11-07-2018, 09:09 AM
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Adblink/back uo light issue

Hey Adblink, just wondering if you found the cause of you back up lights staying on. Am interested in what the problem was.
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