OK, I’m not making this up… My 1986 Turbo Z dies (looses electrical power)when I press on the brakes. But only the FIRST time… If I tap the brakes and immediately press on them or pump them, the dash (electronic, notorious for corroded gold fingers on the power and signal connectors) only goes out on the first press. If I stop or slow down, then go a little farther, and press the brake again, sure enough, the first time the lights go out (and if I’m not fast enough to let off, then pump it, it DIES right in the middle of traffic!) And the problem gets worse when the weather is hot.
I presume it’s a ground, open or short, (or capacitive charging, or inductive loading, or electrical overload from the air condition, or years of gunk where no respectable engineer ever dreamed it could accumulate, or the wiring modifications some ##$% made to add a security device, or, OR???) but HOW do I find it?
Well, that’s weird enough.
My first guess would be the battery and or the battery cables. The idea would be that the battery when cold isn’t able to deliver enough voltage to keep the electronics running and simultaneously power the brake lights. Keeping the brakes on heats up the battery which then delivers a bit more voltage and everything works … for a while. Not much of a theory I’m afraid, but it is a theory.
If you have a multimeter, check the voltage at the battery terminals with the brakes on and off? It really shouldn’t drop much at all when the brake lights go on.
Maybe clean the battery terminals and see if the problem goes away for a while? If so, get the battery and charging system tested?