Turn signals

What truck?

 

In general, I'd recommend tapping in at the front fender. Quite possible the turn signal switch in the cab feeds a relay and not the actual lights. This is done to allow the turn signal in the cab to be a smaller wire drawing alot less amperage. Anyway, lots of advantages to having the turn signal switch feeding a relay and not the actual lights, and, to the best of my knowledge, is the usual scheme.
However, I only know from common knowledge and do not know for certain on the specific year and model you mentioned.

 

There's no *power* relay for the turn signals unless someone added it

There should be a connector on either side with four wires, it's labeled 'mirror options' on the wiring diagram. I can't remember if it's in the door, pretty sure it's in the cab somewhere around where the wires would pass through to the door

Left side will have 302,228,5, 239
Right side will have 302, 227, 5, 239

302 is for mirror heat
227/228 are turn lights
5 is for clearance lights
239 is ground

 

Your should have alittleore clarification when you make a statement .. there is a turn signal flasher relay.. so technically there is a relay
And if the lights he is installing on the mirrors are LED he's probably gonning to have to change that relay to get them to fire..

 

The post above mine wasn't talking about the flasher. They stated that there may be a power relay

Regardless, I edited my post

 

No you need to add blinker fluid.....everyone seems to forget this step...

 

I'am following you now LOL.. my fault for misunderstanding you