Headlights On When Car is Off/Parked and Raining - S550

MechWolf18

Member
Nov 25, 2019
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29
Maryland
Hello,

I have an interesting problem. When my 2017 Mustang GT is parked/off and it is raining outside, for some reason my headlights may or may not turn on. I have tried a couple things like placing the headlight switch in the "off" position rather than keeping it in the "automatic" position, but nevertheless, the lights will come on no matter the position. I've literally had the battery drain because of this issue. Does anyone else have this issue? My thought is either it is a bad headlight switch, wiring issue, or something with the auto-entry function is allowing the car to unlock itself during the rain, thus turning on the headlights. Any ideas?
 
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17P51GT

Member
Aug 17, 2018
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Los Angeles
Hello,

I have an interesting problem. When my 2017 Mustang GT is parked/off and it is raining outside, for some reason my headlights may or may not turn on. I have tried a couple things like placing the headlight switch in the "off" position rather than keeping it in the "automatic" position, but nevertheless, the lights will come on no matter the position. I've literally had the battery drain because of this issue. Does anyone else have this issue? My thought is either it is a bad headlight switch, wiring issue, or something with the auto-entry function is allowing the car to unlock itself during the rain, thus turning on the headlights. Any ideas?
I would take it to the dealer and have them take a look. Are you still under warranty? I have a 17 GT Premium but no issues so far.
 

MechWolf18

Member
Nov 25, 2019
4
4
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29
Maryland
So the car is actually at the dealer, under warranty, and it has been there for 5 weeks... The issue has appeared twice while at the dealer with the battery draining once. They tell me that they cannot figure it out because they cannot duplicate the problem even though it has happened twice while being there.
 
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MechWolf18

Member
Nov 25, 2019
4
4
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Maryland
So they found out that there were some body seams not sealed properly in the right front wheel well area (passenger side). These seams were leaking water and that water was getting to the BCM, which is mounted in the passenger right side kick panel area (sort of between the floor and the dash, right behind a panel next to the door). The water was shorting out contacts and causing the headlights to turn on, killing the battery, and then giving me a steering assist fault issue. So the seam, which is seemingly (pun intended) between the BCM and front passenger tire was leaking the water. The dealer said Ford had no fix for this and they ended up buying an aftermarket sealer and sealing all the seams in the area. The fix to the seams seems to be working finally. It was a nightmare dealing with the dealer and Ford customer service for a year. You will be the only other person I have found to have this problem if it turns out to be the same thing.

I wish you luck, let me know how it goes! Hope this will prove to be helpful.


What ended up being the issue with your Mustang? My 17 GT was doing this the other day.
 
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bigblokstang

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Feb 10, 2002
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Thanks for the info. I'm not sure if that's what was going on with mine or not. I think mine was sensing heavy rain in the exterior door handle, along with my fob being too close to where I was parked. I bought an RFID blocking box to store the fobs in and that seems to have solved the problem.