When I apply the truck brakes the red brake light in rear doesn't come on for either side. When I turn on the head lights the red tail lights come on but when I apply the brake the light does not brighten to indicate the brake is applied.

Redid one frame ground changed both bulbs for red lens and found no fuse blown. So, can you tell me what it could be?

Thanks

Check out the brake switch

Most are located under the dash I’m not a 100% sure what yours looks like some look like a cigar cutter if that helps any.

It could be wiring its self. I have one that does the same, but runs trailer light fine. I have messed with it for all I am going too. The PU stays at the house most the time now. I use it hauling fire wood on my property is about it now.

Try your 4-way flashers - let us know what happens. What kind of truck/pick-up is it?

First off, look at the upper/center mount brake light on the back of the cab, and see if it's working. If it's working, then the brake switch is fine.

If it's not the bulbs..... because the parking lights come on, we can eliminate it being a ground-side problem, as the brake lights and parking lights share a ground. So you'd need a wiring diagram (which can likely be found online) and to start looking at the power side.

I would start with the switch also

It was used too much when it was new.

Make sure it has a dual filament bulbs and not single filament bulbs for the tail lights. Should be an 1157.

Yep dual filament bulb. I did locate the switch and will take the bottom under steering wheel panel off tomorrow. I can then remove the switch. It looks like the switch is held in when brake isn't applied. When applying the break it releases the switch button. I may just need adjustment or it is bad would be my guess now.
The box roof brake light does work either and doesn't come on when lights are on. The red tail lights do work fine when headlights are. Thank You all very much and I will update my finding.

The 3rd brake light is linked to that same switch if it still works, adjusting the switch on some styles can fix the problem if the switch is a working switch.

Here’s a 90 without cruse control I found a pic of should be a simple nut adjustment to adjust or remove the nut to replace with a new switch. Back up to a building to see if the lights are working to test if the switch is working before replacing it. (unless you can run really really fast) lol

Borrow a multi meter if you dont have one. Just check continuity. Or use a test light and the battery. A piece of wire to one battery post and test light to the other.

check 4 ways and turn signals while you are at it.

if 4 ways and turn signals work , a test light or volt meter at that the BOO (brake on off) switch is the place to start looking.

I wish I was fluent in multimeter.
Stuck here with no spark.
Multimeter demo be
well attended at rondy lol.

Actually not s bad idea for a demo. "Trapping rig repair and maintenance".

Really though you can do 90% of your electrical testing with a test light checking for power and ground. Needing to know exact voltage or resistance isn't necessary for most basic diag.

here is a video to help explain digital multi meters



however yes a test light will tell you most of what you need to know for diagnosing basic auto wiring