99 Chevy Tahoe... Rear turn signals, brake lights, and hazards

Any ideas on what else to check?
Yeah, hook up a professional grade scan tool an check for DTC'S -diagnostic trouble codes in the BCM - body control module. Seeing how it controls (turns on) these lights. Turn/hazard indicators flashing fast means a bad bulb or short circuit somewhere.

DTC B3949: Right Front Turn Signal Circuit
Circuit/System Description
Ground is applied at all times at G200 to the turn signal/multifunction switch. The turn signal lamps may only be activated with the ignition switch in the ON or START position. When the turn signal/multifunction switch is placed in either the TURN RIGHT or TURN LEFT position, ground is applied to the body control module (BCM) through either the right turn or left turn signal switch signal circuit. The BCM then applies a pulsating voltage to the front and rear turn signal lamps through their respective control circuits. When a turn signal request is received by the BCM, a serial data message is sent to the instrument panel cluster (IPC) requesting the respective turn signal indicator be pulsed ON and OFF.

DTC B3951: Right Rear Turn Signal Circuit
DTC B3951 will set when the BCM detects a short to ground or an open/high resistance in the RR turn signal control circuit.

DTC B3950: Left Rear Turn Signal Circuit

DTC B3948: Left Front Turn Signal Circuit

DTC B3445: Stop Lamp Circuit

If the bulbs are lighting but not flashing it is probably the flasher unit relay or a faulty signal switch. Have you checked to see if they flash using the Hazard light switch? Relays are usually a cheap part so try replacing it.

Check for a bad ground as all you have stated could be the result of a ground wire with a bad connection get back to me if you need more help Thanks Ray

I can almost 100% guaranty the turn signal switch is the problem. Power for the brake lights starts at the brake switch. power then splits from there and the third brake light gets power directly from the brake switch. Since the turn signal and the brake lights are on the same bulb power for the brake lights is routed through the turn signal switch. the switch depending on what position it is in will allow brake power or turn signal power to there respective left or right brake/turn bulbs.

If you hold your foot on the brake pedal and wiggle the turn signal and or play with the hazard switch the brake lights will almost always intermittently start to work. this will confirm a bad turn signal switch which is pretty common on GM vehicle with this style setup.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

lol sounds like my old truck most likely crossed wires

could be something in the turn signal switch

do an electrical check of all wiring to all the lights, you are describing the symptoms of a bad ground , bu i don,t have enough info to gues if its front or rear,

sounds like one of the circuit bords at taillights is bad

Did you ever figure this out? I've got the same exact problem with my tahoe.

I have a 2002 Chev Cavalier that had the same exact problem. I replaced the bulb harness (purchased from a chevy dealership for around $5) which was fairly easy to do. I have had zero problems with it since.