I have searched all over the place and have yet to be able to diagnose this issue

89 740 GL With no working brake lights

brand new bulb failure warning sensor, fuse is good, brand new brake light switch and still nothing

would appreciate any other ideas or input

 

time to trace out the circuit with a volt meter. is there power at the brake light switch? is there power at the wires to the fixtures ?

 

I had a bulb-out signal. Turn signals, back-up lights, and running lights were all working. I did not wiggle the brake light bulbs. I did not check and see that there components were corroded and melted. Not brake failure relay. Not brake pedal switch. Every contact was checked twice and passed, before the source was found. As a temporary fix tabs were bent more to make contact. Replacement taillights are being ordered.

As a coincidence, the center window brake light had gone out at the same time as the total brake light failure, or so it seemed. It turned out that that center bulb was bad.

Remember that the test meter showed that everything was making contact. The left tail light got all the focus due to wiring. The right tail light was ignored until the wiggle and pull of the taillight unit. You could smell the corrosion.

The worst part of this is that I did not try the wiggle myself, nor pull the units for inspection, but even the professional did that last based on connection checks. Do this first if both brake lights go out simultaneously... or anyway. You could say that the meter checks would be the second, rather than the first approach. My car is a 1990 740 GL wagon.