Brake lights getting cross fed power?

[jaluhn83]

Computer should be under the dash just left of the trans hump. It's a black box on a bracket screwed to the bottom frame of the dash.

 

[kc0stp]

So unplugged the bronze box and black box with no change (pretty sure bronze was ABS) only module I didn't unplug was the white plastic one which Im guessing is just the buzzer for the door being open. Also confirmed that with all lights unplugged from the harness (disconnected at factory hardshell) its putting out 9.5 volts vs the 4.5 Im getting with the lights plugged in.

 

[franklin2]

Well, the voltage is obviously coming from something on the lightgreen wire. You might want to check this wire to verify, it's the one going in and coming out of the brake switch on the pedal. The 89 diagram shows this wire going to the turnsignal switch and then makes it's way to the rear lights. It also shows the ABS and the cruise on this lightgreen wire. Your electric brake control will also be tied into the lightgreen wire.

 

[jaluhn83]

Interesting. Try disconnecting the brake light switch and turn signal switch. Turn signal switch is the grey semi circular connected next to the steering column under the dash.

 

[kc0stp]

First two things I tried, ended up replacing the brake switch and the first 8" of harness (no change, same story with switch unplugged) unplugged T/S and power goes away but a new switch has the same power to the back. Also noticed while picking up some lumber that the ABS light is on now so its probably connected.

 

[79jasper]

Be good to see if multiple other peoples trucks are doing the same.
Just to see if it's in the design, or a faulty part.


Sent from my iPhone using Tapatalk

 

[jaluhn83]

Ok, so it's upstream of the turn signal switch - looking at the wiring diagram, the output side of the brake lt switch also ties to the E4OD ECU & the ABS ECU - try unplugging both of these. Can't recall if you said you'd tried the ABS already or not.