1996 2500 4X4 5speed RWAL. My ABS and Brake lights have been coming on. I know these trucks have issues with the stoplight switch & speed sensor. The only thing is that the lights are coming on and off completely at random. Most recently they hadn't come on for over 2 weeks. Then all of a sudden they popped up this morning and have been coming on/going out all day. They'll come on fairly consistently for a couple of days, then just stop coming on all together for a week or more. Over the course of 3 months the lights have come on both hot/cold, when braking/when not braking, forward/reverse, bumpy/smooth roads, neutral/in gear, idling/70mph. Sometimes the lights are solid, sometimes they flicker, sometimes they're full on, sometimes they're dim. You name it, it's done it. Sometimes the lights go out on their own, sometimes I have to cycle the key. The only thing that has been consistent about it is the fact that it hasn't been consistent at all, lol!! Vacuum seems to be good, fluid level is okay, stopping power is decent considering I'm spinning 35s. The pedal feels alright and is consistent, brakelights work, speedo works, replaced bulbs, I tried jiggling the wires at the ABS brain and at the proportioning valve and neither make the lights flash. Brake booster? Master cylinder? Proportioning valve? Calipers/wheel cylinders? Speed sensor? Stoplight switch? Vacuum switch? I think my next plan is to flush the DOT 3 but would love to compare ideas with you. Thanks in advance guys.