No rear lights?

First of all, thank you for responding back and willing to help it means a lot. Just so we on same subject the white wire I'm referring to is coming from fuse box and the brake lamp relay is in spot where wire is coming from n not attached. I'm trying to see where it would splice in a wire for brake light switch because white wire is at most 4 inches long so can't go back in fire wall. Going out to truck here in few minutes and will take pictures of wiring and so that way you can see and know exactly what I'm talking about clearly and able see what I'm seeing.

That's the white wire I am asking about don't see where old one is or where it connects to.

Okay, so is there a certain wire I hook up to or just use a wire with power to it? Also use a constant power or a power with key in the on position? Come to learn guy that supposedly knew what he was doing when didn't had replaced fuse box and cut old wires to wire in new one and didn't connect all wires and ran different wires to third light to get power to other rear brake lights. Asking about wires so I'm hooking up right to figure out and as you say to. Again, really appreciate the help and time and advise you giving me especially your time responding.

Okay, so got power to it and it's working way it's supposed to when brake is pressed. When turn lights on everything turns on and works except no parking lights in the rear but do have brake lights if I apply the brake. If you press the hazard light button on steering column, they flash in rear. So, I have all the lights in front working have flashers in rear, all brake lights working but no parking lights in rear. Thanks for advice on brake light issue and getting it repaired.

Okay, will try that and let you know. Question got another issue all of a sudden come out to start up truck and it will crank but will not fire over at all. Now just did all new plugs and wires already checked to see if get fuel to engine from fuel rail pressure valve it is getting fuel none of spark plug wires are arched or exposed after turning it over for few seconds it makes like a backfire noise in the air filter cabin. First time ever did this never had issue with it starting up before had it running for over an hour yesterday and ran perfect no problems never shut off not any noises or smoke at all was running and sounding great and now nothing at all must cranks and cranks. It's like it's not getting spark now to fire it over. Had a similar experience with an 1985 chevy caprice years ago turned out to be the ignition module I believe it was it sat right under distributor cap was white and flat and then it was can remember wat it was called but it was round black hard rubber in middle and a metal square housing around it it also was connected to distributor cap and had wire connection plugs to it. But that was am 1985 Caprice this is 1997 GMC suburban.

Okay, got rear lights working like should just one issue still. Checked all fuses and tested lights. So, what is going on now is press brake pedal and rear brakes lights work use turn signal left n right and works in rear turn on parking lights and nothing still. But now if take rear light assembly off and disconnect light and use tester light it has power to all wires in the rear light assembly on both sides and all other parking lights are working just don't have no parking lights in either side in rear.

Yes, there is power on both sides at light assembly in rear. Test lighted all wires in connections during each wire did what supposed to do the brake lights light up when pressing brake yellow wire driver side rear make lights blink up test light all lights work right just has no running/ parking lights. So quick rundown and hopefully helps you and knocks it down to figuring it more less what is causing this. Have all functioning and working lights in front of truck in rear have turn signals have hazards if press it. Has brake lights when press brake pedal but turn light switch on dash on to turn on lights no parking lights in rear.

Here's a short video of my issue that I'm going through with taillights. Sorry about the shake video it's just me recording or trying to holding my tablet n not trying to drop it.

Okay, and thank you on comment of video. So, after getting it all back together I noticed all the lights were functioning well, almost all. If you start the truck up and press brake pedal rear brake lights, come on even 3rd light on top. Both turn signals on left side work front n rear same as for right side, all hazard lights flash as supposed to. Here is the puzzling part: when I turn on my lights all the lights around truck come on as they should but now yes, my rear taillights are showing on but when looking closely notice all 3 brake lights are on as if pressing brake pedal and I'm not. But turn lights all off and all lights are off and brake lights off too and will turn on if press pedal. I also noticed that there is another wire a light blue thick wire that comes from under the brake light relay under hood that was not wired together with another light blue wire its connected to a white wire coming out of firewall in engine area which looks to be wiring harness that traces back to rear lights wiring. So, me being curious I disconnected lt blue wire from white harness wire and it causes me to lose brake lights when pressed and causes me to have no lights when I turn on lights switch on dash. But connect wire again and I can hear the brake light relay click and taillights are on again and has brake lights again disconnect light blue wire again and no lights. Can it be possible that the light blue wire and white wire that are coming out under the Brake Light Relay in engine compartment are spliced into wrong connection point. Because if I disconnect white wire it does exactly the same thing light blue wire does causes to lose all rear lights when lights are turned on and loses brake lights if pressed. So, it's all acting correct if drive during daytime I'm good but at night can't drive because looks as if I'm riding brake pedal even when not but do have all lights working even reverse light is working when put in reverse. Now that's with those wires connected if either wire is disconnected I have no brake lights or taillights. After looking over and under and all thru area wires are in cannot for life of me find anywhere else these wires are able connect to and diagrams you sent me there showing connecting to harness for brake light switch and to directional switch but wires not long enough to connect to them. I came to conclusion that either brothers buddy cut wires to short and thats why I am not able to locate where attach at and that my issue is between relay wires wired wrong under hood compartment between the light blue wire and the white wire.

Traced followed each wire and they all are running n connecting as diagrams are saying should. Tracked it down to 2 separate wires but both coming out from the brake light relay under hood. The terminals that the brake light relay connect into are the 2 wires I have traced my issue to its that white wire and a light blue wire from relay that isn't wired correctly. In the diagrams you sent me all of them show white wire from brake light switch to brake light relay are to connect and shows light blue wire connecting to the turn signal switch wires. The way they are connected is white and light blue connected with a thick pink wire from fuse box all together and then about a half foot down the harness the white wire is connected to brown wire and light blue connected to white wire in same harness going to rear lights to connect to light assembly. And both light panels on each side were replaced already.