S10 wiring issue need help asap!

Okay y'all I've got a 1998 chevy s10 extended cab 5speed. When I turn my key to the on position or start my truck my tail lights shut off and my running lights and brake lights. When the key is off and I turn my lights off and push my peddle down they work find?!. I replaced all bulbs and fuses.now when I turn the key on and the lights i tryed tested the new bulbs and when I turn on my blinker it don't flash it stays solid still no lights in the back till every thing is shut off. I can't figure it out I tuck the front clip off the bed off the dash out I've looked threw it all I checked the ground redone it. What could it be?! Please help it's been parked for weeks due to this issue

Check the diode in the UEC for the DRL system. Also check ground connections at all exterior lamps.

I got from the head lights to the fuse box stripped every body ground I found was rusted up gunna clean all that and redo them and put it back together and do the back the same way hopefully this helps. I have no idea what the diode or the uec is?.

Underhood Electrical Center - It is a fuse/breaker/relay panel under the hood. One of the positions contains a diode in place of an ATO type fuse. This is used to supply power to the daytime running lamps when the engine is running and parking brake is off.

Okay I redone all grounds changed all bulbs and fuses. Now I have brake lights and turn signals when the truck is running. But on the left side the knob that turns the running lights on when I turn that on it kills my tail lights. I still don't have running lights. And I've found something else out when the truck is off I can push my brake in the tails work and my air bag indicator lights up and it dings when the brake is pushed in I let off and it stops. Almost like a wire is grounding out put some were. I redone and went threw the front harness to all front lights only thing left is the wires running down the rail to brake lights. Should I untape all that and go threw it as well?. If this don't work I assume it's a relay or something

Okay. I unplugged my harness for my rear lights turned truck on and turned my turn signals on and touched it and it worked fine the test light flashed like a turn signal help would be nice

Again, verify all the connections, and especially the lamp grounding.

Yes I redone all the grounds with new sends and new bolts. And I switched around all the relays under the hood they all work good

Checked all wires all ground I replaced the part under brake peddle. It's keeps blowing a fuse the RTHDLP. And somebody has a wire running from driver side headlight to passenger side head light when u take it off it shuts off like it's not getting power like it don't shut off but it lights up very very little

Thanks for the help. Just gunna replace front back harnesses and inside harness. Light switch and turn signal switch done replaced brake switch