both brake lights quit working, don't know why

[purple_fluffer]

both brake lights quit working at the same time. can't figure out why. 98 ranger

- running lights work, and that is the same bulb as the brake lights (Sylvania 3157, dual filament)

- hazards and turn signals work (Sylvania 3156, single filament)

- reverse lights don't work, haven't for a long time (Sylvania 3156, single filament)

pulled all 6 bulbs and tested with 12V power supply. all work. both filaments on 3157 work. all bulbs are good.

contacts to the brake lights don't get power when the brake pedal is pushed.

hard to tell which fuses to check, so pulled them all. none blown.

checked function with a multimeter for these: does power turn on and off when brake pedal is pushed?

# AMPS TEST
3 7.5 NO
7 7.5 NO
9 10 YES
13 20 YES
16 30 NO
22 20 NO

#9 and #13 get power when the brake pedal is pushed. otherwise off.

removed the brake pedal switch. the contacts are marked with numbers. switch says part# F87B-134870-AB

checked with a multimeter. on the plug, #1 and #3 have 12V power. on the switch, 1-2 and 3-4 have continuity when pedal is pushed, otherwise not. 4-5 always have continuity unless pedal is pushed. any other combination is always off.

checked the tail lamp harness under the rear bumper. it's got 6 pins but was made for 8. if you hold the male plug with the blank spots on the left, and number them like this

[blank][1][2][3]
[blank][4][5][6]

turn on the running lights, [6] gets power.
turn on the hazards, [3] and [5] get power.
press the brake pedal, none get power.

I don't know what could be wrong.

 

[sgtsandman]

Have you checked the grounds? I believe they are right by the tail light housings.

 

[purple_fluffer]

I don't see any ground wires around there. only wires wrapped in cable sheath, a connector under the bumper (driver's side), and more cable sheath going straight to the bulbs.

that connector was clean and dry inside. same for the 2 connectors next to the fuel filter.