Where is the brake light censor switch located on a Peterbilt 587?

Answer 1

There's a switch to actuate the brake lights, but there isn't a sensor of any sort. That uses uses an SAE J1939 multiplex system. What that means is that, when you press that brake pedal and actuates that switch, instead of power going from the switch to the relay then to the lights (as it did on older systems), it instead sends current to a chassis node computer. The computer reads that input, follows the programming, and send output current to the appropriate outlet port. If it detects an inadequate amount of amperage being drawn, then it knows there's a fault in the circuit. That's how it's able to display the message, make the turn signals flash faster when there's a fault in that circuit, etc. If you have the body control module program (ESA - Electronic Service Analyst - is the program PACCAR uses for Peterbilt, Kenworth, and DAF trucks), and the programming can be altered in many ways, but the factory default settings are the way they are for a reason. The chassis node itself... not familiar with that exact model, but it's typically mounted on the left side frame rail, and all electrical components which aren't part of the engine system are tied into it... As for the switch itself, it'll be on the end of the brake pedal arm. If you test it and get continuity with it depressed, then your issue is elsewhere.