i have a 04 supercrew w/ tow package the break lights and turn signals work the problem is that i have 12v at the parking light on th trailer when i put a bulb in it doesn't light up and my tester only reads around 3v tried w/ different/new bulbs and checked fuse #10 and relay 201 cant figure out why they wont turn on any help would be great

 

How did you check the fuse and relay ?

 

i took the fuse out it looked fine but i put a new one in and i swapped the fog light and trailer tow park lamp relay and the truck still did the same thing

 

remove and replace some times is a valid check, but if there was a problem, you could have smoked new parts.

Try checking the relay socket for the trailer tow parking lamps.

Pull the relay, and check for power to the common pin on the normally open contacts, pin #3.

If you have power there, you can jumper the normally open contacts ( pins 3 & 5, shown below ), and check at the trailer tow adapter, to see if there is a wiring issue.

If you have power, there is an issue with the coil ( or power to it ), if you do not have power, there is something wrong with the wiring.





Next time, checking the fuse is using a meter to check for power on both sides ( with it installed in the slot ), with the pins on the back of the fuse.


Testing the relay is pulling it, and applying power & ground to the coil, and checking resistance through the normally open contacts.

 

ok i have 12v at pin 3 there is 12v at the trailer adapter after i jump from 3 to 5 and the parking light is turning on even when the head light switch is off when you say If you have power, there is an issue with the coil ( or power to it ) do u mean the coil in the relay (bad relay) or something else

 

Ok, that is the correct operation, the trailer light plug should be hot with the jumper in place.

Next is to test the power from the parking lamps to the coil on the relay.
This is pin #2, but check with a meter on pin #1 & pin #2, this should give you + and ground.

This test is done with the main headlamp switch turned to the park position, and is testing the parking lamp circuit to the relay socket.

 

SSCULLY i want to thank you for helping me i went out to do the last thing you said to try i plug in the relay and it clicked and a buddy of mine told me the parking light came on. I did not do anything but what u told me to check and they are now working i will double check again tomorrow if it is not working again i will do what u said in your last post and let you know the results and hopefully u will still be able to help THANKS AGAIN