Truck Repair Electrical Problem


New Member
Have 1999 Volvo , No brake lights, Have signal lights, backup, running ,
Hit the brakes no lights on tractor. Changed fuses still nothing.

All suggestions helpfull


New Member
On the tractor, bulbs are good, fuse is good
When you step on brakes no brake lights, signals work
no power lose.
Do you know if there is a relay somewhere?

Skateboard puller

Hozer Witta Hood
How can your bulbs be good and you have no power loss?

You need to use a test light or multimeter to find out if you’re losing power or ground, and where

Maybe call the dealer for a wiring diagram


New Member
There is no power loss. When you step on the brake no lights , signal light continues to flash like
ti is suppose to do, running lights stay on . Just weird at this point, unless there is a loose
wire but so far nothing.


Well-Known Member
If your trailer and tractor brake lights aren't working then check the switch under the dash at the break peddle . First check that the switch isn't unplugged . If not then try changing it.
If your good enough with simple wiring you can take it out and rig it between a battery and any 12v light . When all connections are made light will be on and when you press button in the light will go out . Then release button light comes back on . Also just check the wiring going to switch with a simple light tester . I think it's always got power going to it even with truck off as long as battery is connected ... as brake light will flash with key off if you hit the brakes .


Friendly Neighborhood Former Technician
Staff member
If your signal lamp is on your brake lamp is over rode. Now if you apply the brake and you have brake lamps on trailer(signals off) and no brakes on the truck you have A a bad relay, B a bad brake lamp switch or c bad wiring at some point between the switch and the lamps