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Message: <blockquote data-quote="Misbuilt R" data-source="post: 2106211" data-attributes="member: 79109"><p>I just experienced this on my Gen 1 SCAB a few months ago. I replaced the third brake light, tested the wheel speed sensors while driving using a professional diagnostic tool, dropped the spare to unplug the wiring harness to the trailer brakes and lights cleaned and add dielectric grease. No joy. I have attached the test procedure from a Gen 1 workshop manual. I used this with my diagnostic tool to determine that the Hydraulic Control Unit (HCU) was bad. Unfortunately the HCU software appears to be specific to the truck. Its needs to be downloaded from the bad HCU and then uploaded to the new HCU making it a dealer visit (unless you know of a shop that can do this). The next pain is that the HCU is no longer available so you are forced to go with a used part (my experience your may differ). On the positive side the HCU can be replaced without disconnecting the brake lines etc. to the antilock pump.  Hope this helps somewhat.</p></blockquote><p></p>