High center stop light acting weird. 93 Shadow

The high center stop light on my wife's 93 shadow had both bulbs burnt
out. I replaced them and they are acting real weird. They come on
when the brakes are not applied (when the regular brake lights are
off) and go off when the brakes are applied (when the regular stop
lights come on).

At the same time there is some interaction with the rear window
defogger controls. When the high center stop light comes on, the
defogger switch light comes on. If you have your foot on the brakes
(and the high center stop light is off) you cannot turn off the
defogger switch, but it your foot is not on the brakes (and the high
center stop light is off) you can turn the defogger switch off.

I'm thinking it could be a ground problem. My Haynes manual only has
"typical" wiring diagrams and these two circuits are not clear to me.
It looks like there may be a common ground for these two circuits,
located in the right "C" piller, but I am not sure. I don't see any
wires leaving the right side of the rear window, only the left side.

Anyone ever have this problem before or have any ideas?

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Get a FSM, start digging. It's probably a chafed wire.

Ted

 

It was a bad ground. When I grounded the one side of the High Center
Brake light with a clip lead, everything worked normal. So I ran a new
ground wire from the body to the lift gate and then grounded the one
side of the bulb to the mounting screw right near the light.

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