Stumped: Reverse Lights Stay On
Thread Starter
CMOC Newbie
Joined: Jun 2010
Posts: 12
From: Hamilton, Ont
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 can’t anyone that has experienced the same problem.
Any suggestions?
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 can’t anyone that has experienced the same problem.
Any suggestions?
Last edited by adblink; May 5, 2018 at 09:30 PM.
Thread Starter
CMOC Newbie
Joined: Jun 2010
Posts: 12
From: Hamilton, Ont
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
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
Thread Starter
CMOC Newbie
Joined: Jun 2010
Posts: 12
From: Hamilton, Ont
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.
Doing something I didn't think I'd ever have to. Taking it to the dealer this Wednesday.
CMOC Rookie
Joined: Feb 2017
Posts: 35
From: Exeter Ontario
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
CMOC Newbie
Joined: Oct 2018
Posts: 19
From: Dartmouth NS
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
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; Nov 1, 2018 at 08:49 PM.
CMOC Newbie
Joined: May 2018
Posts: 22
From: Toronto
I have no familiarity with the transmission in question. On my British cars there was always a switch on the transmission which could be adjusted for travel with a locking nut. I actually had to adjust this on my TR8 as my problem was the reverse, the lights were not coming on. Perhaps look for a switch issue.
Thread Starter
CMOC Newbie
Joined: Jun 2010
Posts: 12
From: Hamilton, Ont
sorry guys that I didn't respond with the solution. Bad form. I wasn't happy with the outcome but at least I was happy that I checked everything that I could and my diagnosis was correct. It was the BCM (body control module) that is located in the right side of the trunk mounted to a frame.
It cost me in the neighborhood of $400CAD to get it fixed because it also required programming so I got charged for that as well. It was obviously not a common part because they had to ship it from down in the US somewhere to up here in Ontario. No word on how this could happen, but I'm blaming my trickle charger. I'm not putting that thing on the battery again.
It cost me in the neighborhood of $400CAD to get it fixed because it also required programming so I got charged for that as well. It was obviously not a common part because they had to ship it from down in the US somewhere to up here in Ontario. No word on how this could happen, but I'm blaming my trickle charger. I'm not putting that thing on the battery again.
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