Wiring Diagram Second Look - 96 Dodge Ram Brake Warning Light

JHZR2

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My 4wd Ram hasn’t had a functioning brake light since Ive owned it. It has a brake controller for trailering, and the brakes all work perfect. No issues with vac assist, fluid, parking brake, etc. Just no dummy light, either at the light check at startup, nor when the parking brake is applied, etc.

I think based upon this diagram, the brake light bulb should always have a hot side. Assuming the fuses are in place and functional (they are). So I should be able to probe with my meter and find 12v when the truck is on, on one side of the bulb socket. Does anyone disagree?

8A3B1A21-9819-4449-8AA7-34BD2A33BFE5.jpg


The other odd thing is the vacuum sensor. The brakes are vac assisted, and the abs and brake warning light will illuminate when vac is too low. It’s strange to me that it isnt just a switch, there’s voltage to it. I’m assuming that it’s some sort of active switch that connects to ground when it senses vac is too low. Anyone else understand how these sorts of vacuum sense switches work? I don’t think there’s a need for a biased signal, there’s no AT that is basing shifting on vacuum (as in my diesel Mercedes), and it only feeds dummy lights.

Any thoughts?

E5209156-FD53-459D-99FD-61554BC29DEB.jpg
 
1) That is a pretty crappy diagram so I can understand the confusion.

2) That is not the right wiring diagram page since it doesn't even show the brake light bulbs in the circuit, and yet, it does show the brake switch connected to ground, so I do agree that it's "probable" that the circuit should be hot, except for one thing.

3) Brake lights tend to work even when the engine isn't on, so there has to be more to the circuit than that diagram shows.

At a minimum what you can do still is check the fuse for the brake lights, get access to a socket and check for 12V, and for ground, both with and without applying the brake pedal.

I doubt you need to focus on the vac sensor at all. It's a safety imperative that brakes and lights continue to work even with no vac.
 
1) That is a pretty crappy diagram so I can understand the confusion.

2) That is not the right wiring diagram page since it doesn't even show the brake light bulbs in the circuit, and yet, it does show the brake switch connected to ground, so I do agree that it's "probable" that the circuit should be hot, except for one thing.

3) Brake lights tend to work even when the engine isn't on, so there has to be more to the circuit than that diagram shows.

At a minimum what you can do still is check the fuse for the brake lights, get access to a socket and check for 12V, and for ground, both with and without applying the brake pedal.

I doubt you need to focus on the vac sensor at all. It's a safety imperative that brakes and lights continue to work even with no vac.
Occam’s Razor came to pass here… was a bad bulb. I could have sworn that I had checked the bulb resistance as the first thing I did, but I’m not sure. Maybe the connector is even bent. It was hard to put in.

Brake warning lights don’t work with ignition off. This was the dummy light in the cluster, not the physical brake lights. There are sources for 12v in all other key positions. The first picture shows the bulb in the circuit.
 
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