Headlights ON = Brake lights ON + No Cruise Control?

Hi all,

Newbie here...I just picked up a 1999 3.6L 4x4 and I have an issue with my dashlights/brake lights/headlights/cruise control. I have a couple of conditions listed below:

HEADLIGHTS OFF:
- As soon as I apply pressure to the brakes, the dash lights (including accessory panel and radio dimmer) dim. When I let off, they return to normal. (not a problem, moreso an annoyance)
- Cruise control works perfectly fine

HEADLIGHTS ON:
- All 3 brake lights turn on. Under braking conditions, they illuminate a small bit more, but nothing too drastic. (definitely a problem!)
- Cruise control does not work!

I am thinking it might be a bad ground somewhere? Not too sure where to start...I checked fuse continuity and the relays all click over. Any ideas?

 

Or maybe the brake light wire is crossed with the rear tail lights? Where could these two become crossed, at the headlight switch?

 

Does this occur with just the running lights on (not the headlights)?

Do you have a trailer harness? If so, remove it and retest.
If that doesn't work, check the rear tail light grounds for corrosion. The only part in the wiring where the brake light and running light can possibly connect is at the rear brake light bulbs.

 

@nzbrock, yes, as soon as I turn the headlight switch to the first position (running lights) the brake lights also go on.

I removed my trailer harness yesterday as I thought that might be the culprit, but no change...I will try to trace back the rear tail light grounds...do you happen to know where they ground to? I'm not too good with wire harness stuff quite yet, but do all of the grounds connect to the same spot?

 

The grounds will be attached to the outside of the light socket (big metal cylinders behind the light housings). It will be riveted to this and then run into the connector. These rivets fail over time. Also just look for general green corrosion at the connectors. If you don't have a multimeter that can check continuity, you should get one. Very useful for automotive and home stuff. Most ground wires on toyotas are White with a black stripe. On wiring diagrams this is referred to as W-B. This ground wire goes all the way back into the cab through the BN1 connector under the driver seat. This continues on to ground at point IG which is up to the left of the driver side kick panel. I'm not sure if you can see it by removing the kick panel.

A lot of people will just add an extra ground from the tail light harness to the frame when this issue comes up.
I have attached the wiring diagram for the tail light illumination and stop light, as well as the ground points.

 

Many thanks! The diagrams you gave are easier to understand than my Haynes manual... There used to be an aftermarket alarm system that was installed and I removed it since the alarm kept going off after a battery change...this was under the lower dash panel. Wonder if I missed a ground re-connection somewhere...

 

Those diagrams are taken directly from the Factory Service Manual, I don't really trust anything else.

Yea aftermarket alarms, or just any alarm in general are tricky. Especially if they used T-taps to connect to wires, those wires could be damaged now.

 

After hours and hours of looking at my damn wires, turns out I didn't have the correct brake/tail bulb in the rear left tail lamp. Lesson learned, always check bulbs first!

@nzbrock thanks for the diagrams, they were incredibly helpful when looking at my wires at least!

 

Ahhh you knucklehead! At least you're man enough to come back and tell the truth