2017 f150 no trailer brake lights but running lights work
04-28-2018, 01:57 PM
#1
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2017 f150 no trailer brake lights but running lights work
Hello all! I’m having a little problem and hoping to get some answers. I bought my 2017 f150 used. It came with a factory tow electrical hookup. The other day I hooked up a trailer with working lights. I noticed that the running lights on the trailer worked when I turned on the truck lights but the brake and turn signal lights don’t work. I did some research and saw a few threads that talked about a module and fuse that the factory doesn’t install (usually found in the glove box of new trucks for the owner to install). Since my truck is used there isn’t anything in the glove box. What do I need to check &/order to get trailer lights to work properly? I did check the manual and it shows (3) fuses are for trailers. Two of mine have working fuses installed. The third fuse slot only has one blade in it. Any help would be greatly appreciated!
04-28-2018, 03:55 PM
#2
Senior Member
The basic light functions should all work right off the showroom floor. The things that require activation are charging and electric trailer brakes. Get a test light and start probing the plug socket and see if you have power to the stop light terminal. The legend is molded right into the trap door/cover. My guess is the brake light fuse is blown. There are separate fuses for the truck lamps and the trailer supply wire.
04-28-2018, 07:37 PM
#3
Grumpy Old Man
Maintaining all the trailer electrical circuits is frustrating, One big help is to buy and use a trailer plug tester, such as this one:
https://www.etrailer.com/Accessories...y/TR20117.html
But even with that tester, you still have to have someone step on the brakes before the brake light circuit will light up.
If a light on the tester doesn't come on when it should, then your first suspect is the fuse or relay for that circuit.
Last edited by smokeywren; 04-28-2018 at 07:41 PM.
04-29-2018, 04:45 PM
#4
Senior Member
But to check, your helper must be stepping on the brake pedal,
Maintaining all the trailer electrical circuits is frustrating, One big help is to buy and use a trailer plug tester, such as this one:
https://www.etrailer.com/Accessories...y/TR20117.html
But even with that tester, you still have to have someone step on the brakes before the brake light circuit will light up.
If a light on the tester doesn't come on when it should, then your first suspect is the fuse or relay for that circuit.
Maintaining all the trailer electrical circuits is frustrating, One big help is to buy and use a trailer plug tester, such as this one:
https://www.etrailer.com/Accessories...y/TR20117.html
But even with that tester, you still have to have someone step on the brakes before the brake light circuit will light up.
If a light on the tester doesn't come on when it should, then your first suspect is the fuse or relay for that circuit.
04-29-2018, 09:47 PM
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Thanks for the tips, I think I have it working, just need to hook up the trailer or get a tester. I think my harness was loose. I dropped my spare and unplugged the harness then re-plugged it in. A multimeter picked up voltage with the brake and turn signal so I think I’m good!