When headlights are on, no torque converter lock-up.

Hello,

Been having this issue where I have no torque converter lock-up whenever the headlights are on. Additionally the brake lights are also stuck on only when the headlights are switched on. When the headlights are not turned on and I press in the brake pedal, the dashboard back light turns on and the parking lights will turn on. I am wondering if there is a faulty ground but I cannot seem to find where to even look. I have a 96 super custom with the 1kz. Thanks.

Good Evening Desplanches.

Agree with the ground diagnosis.

I’m attaching the ground point locations for the instrument panel, body and engine. Please start there. Recommend you look at the wire too while you are cleaning the connection. My wife’s truck ground wire was secure, but when I wiggled it, corrosion started coming out and it fell apart in my hands.

Hope this helps, it’s a good starting point and I wish you all the luck and success ahead.

God Bless
-Bryan

Yes, Toyota has “clever” ways of grounding circuits with switches that seem to to multiple things internally. If there’s a failure somewhere,  circuits will find other ways to ground causing voltages where they ain’t supposed to be.
It’s likely to be a single thing, like one of the grounds Bryan mentions.

Or a reversed polarity somewhere.

I’d start with making sure the various fuse panel power and gound supplies are well connected.