Reverse Lights Wont Turn Off

[frankenstang]

I'm having a problem with the reverse lights on my 2005 Mustang GT. The reverse lights stay on no matter what gear the car is in and will turn on by themselves when I start the car and wait a couple seconds. If I start the car in reverse the lights will be on right as I start the car, but if started in another gear there is a pause before they turn on.

Some background on the car is that I bought the car wrecked and replaced the whole front end including the PCM and motor and all from a parts car. One downside was the wiring harness going to the PCM on the parts car was cut so i had to swap over the wires into the new plugs. Everything on the car works perfectly besides the reverse lights and cruise control (not working because of reverse lights staying on). So perhaps one wire may have been misplaced?

I checked the reverse lamp switch on the transmission and that tested out to be fine. Unfortunately this led me to believe that the problem may be within the smart junction box (SJB) or a wire going to the PCM may be cut or placed in the wrong spot when transferring to the new plugs. I have tried looking for a PCM pin out for an 05 GT and have not found any. If anybody has a pin out diagram and/or any idea on what else the problem may be it would be greatly appreciated.

 

[Wicked One]

Check the reverse switch on the transmission. Mine did the same thing. It is a cheap fix. Unplug the harness to the reverse switch and see if that helps.

 

[frankenstang]

I checked the reverse switch and replaced it with one that I know works and it did not fix it

 

[JeremyH]

It's a reverse polarity circuit so potential for power is always there and once grounded via the switch on the trans the lights come. If you disconnect the wire plug from the switch at the trans that creates a permanent open and the lights should go out. If they do not, you have a short on the power wire for the circuit allowing it to complete and turn the lights on regardless of switch position. So inspect the power wire from lights to sjb for damage.

 

[frankenstang]

That makes alot of sense because when I unplug the reverse switch the lights still stay on. I'll tear into it and check it out. Im assuming the same applies to the wires between the smart junction box and reverse switch as well.

 

[olds350]

Just food for thought. Check and make sure none of the running and brake lights are out. I mention this because when I hooked up my tire trailer, the lights came on instantly. Couldn't figure out why until I found a blown bulb. Replaced the bulb and the trailers lights functioned normally. The blown blub caused a closed circuit...

 

[frankenstang]

The running and brake lights work perfectly. Its just the reverse lights that I have the problem with. I've gotten away with just unplugging the bulbs for the reverse light until i get time to find the problem.

 

[07gts197]

You can start your car in reverse? Perhaps you have a bad transmission range sensor and so it always thinks youre in reverse or something.

 

[JeremyH]

Its not a sensor is a physical position switch on the trans. Disconnecting the plug from the trans switch ruled that out as issues.