1998 2.5 Ford Ranger
Everything works fine until I turn on my headlights at night
The tail lights act like hazards lights when I use my turn signals, also my 3rd brake light starts flashing
this only happens when my headlight switch is on
I am going to buy a new headlight switch today, but I think it's a bad ground.
I only see 1 ground in the rear of the truck near the rear bumper
Mechanic charges me $300 to look at it... could use some help , thank you

 

Welcome to the forum

The head light power runs thru the multi-function switch(turn signal stalk), so that's more likely the problem than the main light switch

Because main light switch doesn't have access to brake light or turn signal wiring, but all these run thru multi-function switch

 

Sounds like a short in the light harness somewhere. Multi function switch like Ron said. Does the truck have a trailer wiring harness in the back? That could be another place to check.

 

change multi-function switch, nothings changed.

 

Wiring Diagrams for exterior light and headlights below

You should use a volt meter and test the wires at multi-function switch, as you turn on headlights
There should be 2 connectors, C253 and C254

 

Fixed it .Bad ground. I removed the black split loom from the wiring harness.
Followed the wiring harness, started at the rear of the truck. Found a loose ground wire that was previously crimped.
It had come loose. Blinkers work now

 

Good stuff

Thanks for the update and the FIX