I noticed last night that when driving and braking, my high mount brake light is pulsing on and off. Then tonight I realized that when I depress the brake whether the truck is on or off the backlighting for the radio also pulses on and off. What could be causing this and how serious is it?

I should also point out that it only affects the lights because the radio doesn't stop playing. I have a 1997 F150 Lariat 5.4L.

 

I would start with checking the ground at the rear of the truck, and work you way up the body to frame grounds under the truck.

Sounds like the lighting has a weak ground.

 

Thanks Scully I'll check that right now!