So we tested the wires and fixed the couple that were cut. All of it works. Except the brake lights. So now to check the brake switch.
All that being said, it still could be a wiring issue. Check the ground on rear harness that goes from rear light harness, it will/should have a ground that goes to driver side frame rail. It’s a common failure worth checking, but also test(with a test light)for power back there probing to see if you have brake light power(with brakes depressed). Hate to see you install a switch and problem still there.
Hello CamoGoddess13,
As Caman96 stated, the brake lights (GM-speak in wiring diagrams:
stop lamps) not working has indeed
been traced many times to a bad ground out back, especially if the truck has ever been wired for trailering.
GM refers to this ground as
G410, and here's the ground distribution wiring diagram out of the '95 FSM:
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This is the first thing to check. If you can verify that the grounds are clean, providing good continuity
to the bulbs, & all is working as advertised, then the next step is to figure out if the 12v power is making
the trip from the brake switch all the way back to the tail lamps.
Instead of posting screen snaps of this circuit, I have instead attached a 2-page .pdf file so
that you can zoom it up as necessary in order to be able to read the details.
Here's a few hints to help make sense out of this busy area in the wiring harness:
1) The "Stop Lamp / TCC Switch" is on the 1st page. Disregard the (4) bulbs at the bottom of the 1st
page, for these are all the turn & marker lights on the
front of the vehicle.
2) Instead, look for the Left and Right Stop Lamps on the 2nd page. You will trace the wires back and
forth from the brake switch on page 1 to the lamps on page 2 via the 'A inside Triangle' link.
3) About those rear lamps. Ignore the brown wire and associated filaments. Why? The brown wire (circuit #9)
powers all the marker lights, front & rear, making these a Don't Care for now.
4) This gets you down to the
YELLOW (L) and
DK GREEN (R) wires that connect to the Stop Lamp bulbs. These
are the ones that you will be focusing on with your troubleshooting.
5) Following these Stop Lamp wires from the bulbs on the 2nd page to the 1st page, you will see that they don't
go directly to the Brake Switch? That's correct, they are actually connected to the Turn/Hazard switch. (This is
done so that the stop light, turn signal, and Hazard flasher functions can be multiplexed to a single bulb filament.)
In English, if you come to a stop, both lamps are illuminated. But if you subsequently push the turn signal switch down
to indicate a Left turn, then the left stop lamp bulb will flash, while the right stop lamp bulb remains constantly illuminated.)
Q: Can a problem with the Stop Lamp signal be introduced here?
A: Yes. Not unheard of, be aware...but for now let's continue on towards the brake switch.
6) At the upper RH corner of the 1st page there's the Stop Lamp / TCC switch. Looking closely at the output
of the switch, note that there is a *separate* path to the third
CHMSL. (Center High Mounted Stop Lamp)
To the troubleshooter, this is key, for the CHMSL does not go through the Turn/Hazard switch. (!)
Q: Is your high mounted center brake lamp working when the brake pedal is depressed? If it is, then we can
state that the output from the Brake Switch is working. On the other hand, if this 3rd brake light is not working,
then (assuming a good relay, wiring, etc) this is another indicator that there is something wrong with your
brake switch.
7) Last but not least, there's the STOP FUSE protecting the wiring to this circuit. I know that you've already checked
this, but just adding it for completeness.
****
OK, if you were a normal, well-adjusted person no doubt you figured that the wiring between the brake switch and
the rear stop lamps was a straight shot. If you waded through all of the above, now you know that the wiring is
from the brake switch, through the Turn/Hazard switch, and only then out to the Stop Lamps out back. Oh yeah,
that high mounted brake light above the rear window goes through a completely different path and avoids the
Turn/Hazard switch entirely -- and savvy troubleshooters will use this little bit of trivia to their advantage.
I sincerely apologize for the length of this write-up, but I didn't want to just toss out a couple of screen snaps
full of the General's '95-era wiring diagram spaghetti and just turn on the All-U-Can-Eat sign.
Fingers crossed you have already found a bad connection between G410 and your tail lights, and you just skimmed
through the rest of this looking to spice up your Sunday evening with some Fun With Flags Wiring Diagrams. :0)
Best of luck tracking this down. Happy hunting -- 
Sorry, just reread original post and can see you did check bulbs.
