Brake lights work, tail lights dont

[mmrseed]

......but obviously they are the same bulbs. So, my son's 97 expy has an issue. When you turn the headlights on, they come on, but the tail lamps don't. But if you press on the brakes, the brakes light up so it's not the bulbs nor a wiring problem near the back end. Also, his dash lights don't work either. Checked all fuses and they are good. Is the whole switch assembly bad? If so, why do the headlights come on.....any ideas of where to start? Thank you kindly

 

[Thermo]

mmrseed, keep in mind that the tail lights on the truck have 2 filaments in them. You can relate it to the 4HI and 4LO settings in your truck. They use a lot of the same things, but yet, they are different too.

I would first start with trying to put in new tail light bulbs atleast on one side to see if it is nothing more than just a bad filament in the bulb. Next, with the tail light removed, look on the plug going into the taillight, you should see a brown wire there. Using a multimeter or similar tester, see if you have 12 VDC on that wire when the running lights are on. Repeat for the other side when checking the voltages.

If you have 12 VDC there, but the lights are not coming on, then you have a problem inside the tail light housing. If you don't have 12 VDC, then you have a problem in the wiring harness of the truck. Have you done any wiring work on the truck recently (ie, shortly before the lights are thought to have gone out)? If so, I would start in that area looking for any brown wiring that may be damaged/may have been cut.

If you need more help, let me know.

 

[GAINMOB]

my prob was wiring harness...went bad some were and was replaced

 

[mmrseed]

cool, thanks. I got a multimeter and a 12V meter and checked it out and I get no reading at the tail lights. Also, it appears that I was wrong and 4 fuses related to the lights DON'T work, but the fuses themselves are fine, it the slots they are in that don't work....ie, I switched those fuses out and they work in other slots and new ones don't work in those original slots....could a whole section of the fuse box go bad?