On my 03 SCrew, should my trailer lights flash when my hazards are on? My truck only has a 4 pin connector and running, left & right turn signals work fine. Thanks.

 

Yes, in fact this is the easiest way to check function of your lights before driving off.

Turning on the 4 way flashers should flash your tail lights.
This function tests the turn signal and brake lights on the trailer.
Last thing is check parking/marker lights and you are all set.
No need to yell to a driver Right Turn, OK , Now Left Turn, OK, Now hit the Brakes!

Your marker/park lights are not tied into the 4 way flashers or turn signals or your trailer would always flash all the way around every time you turned on a turn signal.

 

Any idea why 4 ways don't flash on the trailer when they are on on the truck?

 

Thanks.

 

My 1st thought is a bad ground.
Sounds like a bad connection on the truck rather than the trailer is everything else functions correctly.

Use a meter and check the resistance on the ground pin against the frame/bumper etc. There should be very little resistance when comparing that to a chassis to chassis ground for a base resistance number.
Sometimes the 4 flat connectors get a bit of corrosion in them and they go bad or get clogged up with corrosion.

When you check the trailer function you can plug it into the truck before connecting the coupler or chains. If nothing works on the trailer you have a bad trailer ground as well.