Third Brake Light on with lights? (1 Viewer)

[mattg141]

'96 80 series, US model.

Is the rear third brake light (on the upper gate) supposed to be on when the headlights are on? I had some brake work done (new booster) and now the third turns on with the headlights. Oddly, the radio light dims when I hit the brakes without the headlights on. I don't remember it doing that before.

Any suggestions?

 

[enox]

Hmmm...

3rd light is just on brakes only, clock dims when I turn the dash lights on because it's tied into the dimmer circuit.

 

[smritte]

You have a ground issue. In the rear, the stop and tail lights share a ground. What's happening is, when you turn on the park lights, the power is feeding to ground through the rear stop filament. When you stop its feeding the other way, that's why you see the radio change when stopping. This is a bug I put into a vehicle for my electrical diagnosis class. It gets them every time.

Pull the rear stop bulbs, if the problem is gone, its in the rear. Reinstall them one at a time and you will find which side. I don't have my book with me at work so I cant tell you what's tied where. I don't remember if our stop lights were dual filament but i think they are. I have actually seen a filament break inside the bulb and connect both together. This could also happen with cheap LED bulbs.

 

[mattg141]

You have a ground issue. In the rear, the stop and tail lights share a ground. What's happening is, when you turn on the park lights, the power is feeding to ground through the rear stop filament. When you stop its feeding the other way, that's why you see the radio change when stopping. This is a bug I put into a vehicle for my electrical diagnosis class. It gets them every time.

Pull the rear stop bulbs, if the problem is gone, its in the rear. Reinstall them one at a time and you will find which side. I don't have my book with me at work so I cant tell you what's tied where. I don't remember if our stop lights were dual filament but i think they are. I have actually seen a filament break inside the bulb and connect both together. This could also happen with cheap LED bulbs.

I will try the bulb trick. However, I just had the brake booster replaced. Is there anything up front (under dash) that it could be?

 

[smritte]

there shouldn't be but never say cant happen. Normally when you have stop and tail lights effecting each other, its in the back or the wire loom going back. If we had some kind of stop light in the front, that would be different. As for under the dash, 1 set of wires is in the steering column and the other is on the brake pedal. I'm not saying impossible but very improbable. Again, never say cant happen.

 

[SteveH]

When the high-mounted stoplight on my '98 4Runner was stuck 'on' 24x7 (with the keys removed), the harness from the hatch had degraded and shorted out in the roof. I carefully spliced in new wires and all is good. You may have a similar problem.

 

[mattg141]

I pulled all the stop lights. Pressing the brake pedal still caused the radio and factory clock to dim. If the radio is aftermarket, could its (possibly sketchy) install be the issue?

Since you teach a class, is there a digital multi meter you recommend?
Thanks for everyone's input.

 

[mattg141]

Update.... when press the brake, the front parking lights also come on.

 

[Kernal]

Does your 80 still have the port/dealer installed trailer harness?

 

[UsedLuxury]

Update.... when press the brake, the front parking lights also come on.

And you want to get rid of this awesome feature?

I pulled all the stop lights. Pressing the brake pedal still caused the radio and factory clock to dim. If the radio is aftermarket, could its (possibly sketchy) install be the issue?

Since you teach a class, is there a digital multi meter you recommend?
Thanks for everyone's input.

Any DMM over $10.99 will do what you need to fix this issue. You have a big issue with your power, I don't know what in the name of meth riddled trailer park walmart hunting aisle you would have to **** up to cause this after a brake booster though. These rigs are wired like a light-brite, not hard to work out. Start at the last known location of disturbance. Try to figure out what hillbilly wire nut job was done. Your brake circuit causing everything else to dim is a good start. You have a short to ground in that circuit. I doubt your radio install is a problem after the install of a brake booster. When all else fails, lower the rig and install underglow.

 

[mattg141]

Does your 80 still have the port/dealer installed trailer harness?

I pulled the trailer connection and it still does this.