No night lights on trailer
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Junior Member
Joined: May 2010
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No night lights on trailer
Hi guys
got a question for you, have a trailer that has working lights with other trucks (Expedition, F250) but with my F150 and a friend's Silverado the lights are working only for brake and left right turn. It seems strange but it works with other cars. Don't know what could be. The F150 has all the lights working fine and could not find a bad fuse.
Thanks
got a question for you, have a trailer that has working lights with other trucks (Expedition, F250) but with my F150 and a friend's Silverado the lights are working only for brake and left right turn. It seems strange but it works with other cars. Don't know what could be. The F150 has all the lights working fine and could not find a bad fuse.
Thanks
Technical Article Contributor
Joined: Jun 2002
Posts: 10,511
Likes: 10
From: Under the flightpath of old ORD 22R
That helps.
Start by checking fuses # 36 & 42 with a meter. They will only have power when the brake lamps or turn signals are on.
Check the pin on the back of the fuse on both sides for power with each test.
Quick way, turn on the 4 ways, or use a broom stick to hold the brake pedal down.
The output of the MFS operates the rear Stop / Turn lamps. This fuse is after the part of the circuit that goes to the truck's stop / turn circuit.
if the fuses test good, next is time to test the 4 pin & pin adapters.
Use the ground on the trailer tow adapter to test with, same thing, the L&R Stop / Turn circuits are only hot when the brake lamps or turn signals are on.
Test both the connectors, and best at this point to test the turn signals 1 at a time, to make sure nothing else is going on.
the back of the 7 pin adapter can get filled with dirt and other assorted crud, that can cause issues.
Once you test the 4 pin adapter, you might find the other trucks are wired incorrectly, or they are using an adapter to change 7 pin to 4 pin, that has been messed with.
A lot of the time, I have seen people repair wiring on trailers, and plug them in, to not have them work correctly, and make a 4 pin to 7 pin jumper to make everything work correctly, rather then take the time to redo the wiring job they just did on the trailer. This is usually followed by several years of not thinking about it, and forgetting that they screwed things up.
The other side ( not as often now ) is the trailer tow adapter is added after the fact on the truck, and does not work, rather than take it apart and do it correctly, they change the trailer plug. This is more common in older trucks when adding a 7 pin trailer tow adapter, it is wired from looking at the trailer plug rather then the outlet view on the truck.
Unless you have a corroded trailer tow adapter or a blown fuse, you might find your truck works fine ( and the other truck ) it is the Expedition & F250 that have been messed with or the common adapter used on them that is the case.
Start by checking fuses # 36 & 42 with a meter. They will only have power when the brake lamps or turn signals are on.
Check the pin on the back of the fuse on both sides for power with each test.
Quick way, turn on the 4 ways, or use a broom stick to hold the brake pedal down.
The output of the MFS operates the rear Stop / Turn lamps. This fuse is after the part of the circuit that goes to the truck's stop / turn circuit.
if the fuses test good, next is time to test the 4 pin & pin adapters.
Use the ground on the trailer tow adapter to test with, same thing, the L&R Stop / Turn circuits are only hot when the brake lamps or turn signals are on.
Test both the connectors, and best at this point to test the turn signals 1 at a time, to make sure nothing else is going on.
the back of the 7 pin adapter can get filled with dirt and other assorted crud, that can cause issues.
Once you test the 4 pin adapter, you might find the other trucks are wired incorrectly, or they are using an adapter to change 7 pin to 4 pin, that has been messed with.
A lot of the time, I have seen people repair wiring on trailers, and plug them in, to not have them work correctly, and make a 4 pin to 7 pin jumper to make everything work correctly, rather then take the time to redo the wiring job they just did on the trailer. This is usually followed by several years of not thinking about it, and forgetting that they screwed things up.
The other side ( not as often now ) is the trailer tow adapter is added after the fact on the truck, and does not work, rather than take it apart and do it correctly, they change the trailer plug. This is more common in older trucks when adding a 7 pin trailer tow adapter, it is wired from looking at the trailer plug rather then the outlet view on the truck.
Unless you have a corroded trailer tow adapter or a blown fuse, you might find your truck works fine ( and the other truck ) it is the Expedition & F250 that have been messed with or the common adapter used on them that is the case.