Well I'll be ... you're exactly right . Looks like our tests after adding them was with no other lights (or brake lights) on. And since I haven't driven behind my son's truck since then, I had no idea. Also looks like I'm gonna work towards adding the two wires into the front turn signal circuits back there when it gets a bit cooler out. Thanks!

 

I think you will need a one way 12v diode somewhere in the turn signal circuit close to the brake switch input and then splice into the circuit before the diode and run your exclusive turn signal wires from there. You'll need one for left and right.

 

Instead of a diode, why not just cut the brake wire from the turnsignal switch? That would turn the two original wires running to the rear from brake/turn to just turn left and turn right. You would then have to cut the wires at the rear and move them to the new amber turn bulbs. Then take the brake wire that was cut under the dash and extend it all the way to the rear and tie it to both old red brake/turn bulbs left and right, and they would both just become brake only. You would have to run just one wire to the rear with this method, but maybe just a little bit more work at the rear taillight area. I believe the hazards would still work properly, blinking the amber turns only.

Can't seem to get away from running wire or wires though.

 

Yes, couple ways to skin this yellow leopard. I was thinking he'd want to keep the red brake lights and turn signals stock and run a seperate L-R rear wires. Really should study up the existing wire diagram before proceeding.

 

You really have to divorce the brake lights completely from the turnsignal switch. If you don't, when you move the lever one of the brake lights will go out since the turnsignal switch will disconnect it.