Long time lurker first time posting, but my driver side brake light will randomly stop working. It is only the actual brake lights as the turn signals work even if the brake light currently isn't. If I turn the headlights on the tail light will light up but still the brake light won't light up when applying the brakes.
It is a very random happening as the brake light will suddenly start working. It doesn't matter if I'm on a bumpy road or just sitting still.
When I hook up the trailer and the brake light stops working the driver side trailer brake light also stops working.
I don't know where to even start looking for the cause, maybe a bad ground?
I need help as I was pulled over by a state trooper who was nice enough to just give me a warning because the light started working as I pulled over to the side of the road.

I forgot to add this is a 2001 blazer 4 door 4x4 LT.
Thank you for any and all help electrical problems are not my cup of tea.

 

Hi

Did you find out what the problem was? I'm having the same problem and cant pass the warrant of fitness to drive on the road.

I'm thinking a ground wire at the rear maybe?

 

It could be a number of things.First check the bulbs.If these are good..Take the bulbs out of it`s sockets.You need a volts meter to see if your getting power to the sockets while someone steps on the break for you.If you have no power at the socket while breaking..Check your grounds underneath the dash coming off of the break switch.last step you`ll have to test the break switch itself.Or you can just take it to a mechanic that`s good with trouble shooting electrical problems.

 

The first thing I would check is the hazard switch. Its contacts control everything for the main tail lights. They are known to be problematic. Sometimes simply cycling the hazards on/off a few times will make the problem go away.

If it doesn't last, replacing just the hazard switch often will. A quick search should turn up the relevant information on diagnosing & replacing the hazard switch itself. If the $18 switch doesn't cure the problem, you'll likely need to replace the entire multifunction switch.

Don't bother checking for grounds to the brake light switch. There are none concerning the switch itself. Also, if it is only affecting one side, you can rest assured that the switch itself is functioning properly.

 

It is only the driver side brake light. I changed the bulbs because at the time I thought they were just blown, and after changing them the light worked, but only temporarily. The brake light works 90% of the time and I'm unsure if it would be a ground as when you turn the lights on they all light up normally. I'm going to climb under and run the line from where the trailer wires split off forward. It has to be forward of this because the trailer light is also effected. The multi-meter is also being broken out of the tool box to do some checking.

 

The hazard switch controls the power flow to the left & right brake/turn filaments in the tail lights. When you hit your brakes and/or turn on your turn signals, the power all flows through the hazard switch. A problem with the hazard switch can cause the symptoms you are experiencing. Failure of the hazard switch is a known issue on the later 2nd gen trucks.

Here are a few threads that will help you along the way:
98+ Hazard Switch Replacement
Broken Hazard Switch Repair

 

It seems to be two problems the earth strap under the battery tray was bad as the front lights stopped working. I pulled up the plastic tail gate trim to expose the wiring also noticed the effected tail light had been cut and rejoined factory recall maybe? I had a good look at the wires and unplugged the terminals and reconnected them all is good now have my warrant recheck booked in for tomorrow.

 

Mine ended up being the multi-function switch. I pressed forward on the turn signal lever and the brake light worked perfectly.
Until I can afford a new switch I'm just going to have to push the lever slightly forward. I have other problems with the truck that I have to iron out.