Lights dim when pressing brake pedal

[Mac442]

1985 442. All lights dim when pressing the brake pedal, whether engine is running or not. I took both bulbs out of both rear tail lights and the dimming doesn't occur. Also with the engine running I hear a small pop in the speakers when hit the brake. I can even ever the blinkers click through the speakers when radio is on. Electrical is not my area or expertise. I've looked at the obvious stuff, but any suggestions would be appreciated?

 

[ELCAM]

First question is has this car ever had trailer wiring on it?

Off the top of my head it is.

Power for the brake lights comes from the headlight switch orange wire to the brake light switch from the brake light switch is a white wire to the turn signal switch from there is is ran over the rear turn signal wires dark green on the pass side and yellow on the drivers side.

I would look for a burned wire of the wires outlined above and especially the white wire going into the turn signal switch connector,

When i get a minute I will check a diagram and correct anything.

 

[Mac442]

Never had trailer wiring.

 

[ELCAM]

Good on the trailer wiring that usually overloads the white wire at the turn signal connector.

The fact that you can hear it in the radio tells me there is a tiny gap in some wire or connector or switch. small enough it can make the circuit poorly but big enough to be what was known 150 years ago as a spark gap transmitter.

If all the wires seem ok try unplugging the turn signal switch connector and plugging it in several times. Also try jumping the wires on the brake light switch with a jumper and see if it solves the problem. The switch contacts might be pitted from arcing making the resistance higher.

 

[565bbchevy]

I would push the brake pedal down with your hand while looking under the dash watching to see if the peddle arm is pushing on any wires up under there when this happens

 

[ELCAM]

I believe this one of the years that have the aluminum wiring to the rear of the car. Aluminum is very prone to breaking. Pull the connector in the trunk and jump the yellow wire to the yellow wire on the turn signal switch. Same for dark green on the passenger side. Bypassing all the aluminum.

The more I think about your first post the more I think the issue is after the turn signal switch in this rear wiring.

 

[pagrunt]

I believe this one of the years that have the aluminum wiring to the rear of the car. Aluminum is very prone to breaking. Pull the connector in the trunk and jump the yellow wire to the yellow wire on the turn signal switch. Same for dark green on the passenger side. Bypassing all the aluminum.

The more I think about your first post the more I think the issue is after the turn signal switch in this rear wiring.

From what I've seen this whole generation of mid-size GM's have that poor choice front to rear harness. Corrosion is another issue with these harnesses.