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Old 07-31-2023, 05:19 PM   #1
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No Brake Lights

Hey everyone - looking for a little help with my brake lights, which stopped working recently. I have 1996 Navistar International 3800 DT466. I replaced the switch at the pedal and a couple of blown fuses. Also checked the light bulbs of course. I see a lot of talk about a possible issue with the brake ground wire - anybody know where the brake wire is grounded typically. Thanks for your help.

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Old 07-31-2023, 05:30 PM   #2
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Join Date: Aug 2020
Location: Alabama
Posts: 420
Year: 1996
Coachwork: BlueBird
Chassis: International 3800
Engine: DT 466 Mech. Spicer 5 speed
Rated Cap: 34
Do you have hydraulic brakes? The reason I ask is that if you do-- they use two switches that are identical-- one for the electric brake booster, and one for the brake lights.

As far as grounds-- seems like each light is grounded to the body near the light.
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Old 07-31-2023, 05:37 PM   #3
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Join Date: Sep 2018
Posts: 2,831
Year: 2007
Coachwork: Thomas Built
Chassis: Minotour
Engine: Chevy Express 3500 6.6l
Do you know if one of the fuses was a brake fuse?

After you replaced the fuse did it blow again? If it did you need to look for a short to ground.

Do you have a multimeter? If you don’t already you can get a cheapie one for $20.

I’m assuming your tail lights are a separate bulb?

The first thing to do is check to see if you have somewhere around 12 volts at the bulb socket. Remove the bulb and while someone (or something) depresses the brake pedal, set your multimeter to volts DC and probe between the center terminal (positive) and the outer casing of the housing (negative). Next, probe between the center terminal and a metal part of the bus (chassis ground, negative). If you have a ground wire to the lamp holder, use the continuity function of the multimeter to check for continuity between it and chassis ground.

You may find it helpful to have some long test leads with alligator clips to perform the continuity tests.

Next, do you have 12 volts into that brake switch? Using your multimeter you can check for voltage there, between chassis ground and that connector
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Old 07-31-2023, 05:49 PM   #4
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Year: 2007
Coachwork: Thomas Built
Chassis: Minotour
Engine: Chevy Express 3500 6.6l
I had a similar problem but just on one side. It was a broken ground wire. I just added an additional ground to the chassis to fix it.

If you have both sides out, I’d tend to think the problem is way upstream and more likely on the positive side, such as a bad fuse or relay.
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Old 08-01-2023, 12:00 PM   #5
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Yes, I have hydraulic brakes. I replaced the two switches (they come together as one unit) and that seemed to fix the problem with the booster, but not the lights. Thanks for the reply and the advice!
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Old 08-01-2023, 12:05 PM   #6
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The brake lights and tail lights share the same bulb, just two different elements. The tail lights work so I am assuming the ground is good. The fuse(s) I replaced did not blow again, but it didn't seem to help the cause which is very puzzling. I do have a multi-meter and just need to start going through all of the wiring. I tend to agree with you that the problem is more than likely on the positive side. Thanks for the quick reply and the advice!
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