ratdude747 Posted April 26, 2022 Author Share Posted April 26, 2022 The cruise issue isn't fixed either... but I also rediscovered that it's not an electrical problem. There's an issue with the brake pedal vacuum valve sometimes not keeping it's seal when the pedal is pressed/released while cruise is active. Tapping the brake and re-resuming usually fixes it. Like a seating issue with the seal? I'll need to pull that valve and see if it's serviceable (as I doubt it's an economically obtainable part?) I think I figured something out... finally was able to reproduce the symptoms consistently: The actual issue is that I'm only losing hazards when the brake light switch is on... which (edit) upon further review is perfectly normal, especially since I don't have a center brake light. I feel like a moron. That's what I get for not remembering my parent's former vehicles (1987 C10, 1988 and 1993 GMC Safari's) without center brake lights... by the time the last one was gone, I wasn't of driving age yet. Doh! Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted April 26, 2022 Share Posted April 26, 2022 I think I figured something out... finally was able to reproduce the symptoms consistently: The actual issue is that I'm only losing hazards when the brake light switch is on... which (edit) upon further review is perfectly normal, especially since I don't have a center brake light. I feel like a moron. That's what I get for not remembering my parent's former vehicles (1987 C10, 1988 and 1993 GMC Safari's) without center brake lights... by the time the last one was gone, I wasn't of driving age yet. Doh! Here's the diagram I can definitely see where a brake light connection to power would override the hazard switch's connection that cycles only when it heats up. (Because it can't heat up if the voltage is the same on both sides of the contacts) Don't beat yourself up for not understanding the circuit if you hadn't looked at it yet. Every day is a good opportunity to learn How would a center brake light change things? Link to comment Share on other sites More sharing options...
Gary Lewis Posted April 26, 2022 Share Posted April 26, 2022 How would a center brake light change things? Yes, that's my question as well. Link to comment Share on other sites More sharing options...
ratdude747 Posted April 26, 2022 Author Share Posted April 26, 2022 How would a center brake light change things? Yes, that's my question as well. With a center brake light, one can flash rear hazards and and still have a brake light working. It was a generalization based off how most US vehicles changed when center brake lights were added to the design. In fact, legally, the only thing allowed to turn on the center brake light *is* the brake, so such isolation is at least partially mandatory. To my knowledge no Bullnoses ever had center brake lights (I don't think it was required for vans/trucks until 1994 or so?) so it's a moot point. --- Based on the EVTM screenshot posted such behavior is normal... and I'm just dumb. Not just a matter of not heating up (or charging up, in my case)... the flasher's bypassed by the brake switch, and due to the way the switch is configured, that bypass is for all hazard lights. Or put another way: The brake switch ties all rear turn/stop filaments to +12V and the hazard switch ties all turn lights (to include the rear turn/stop filaments) to the hazard flasher (a common point). Since there are no diodes in play, when both are on, all are tied to +12V. Link to comment Share on other sites More sharing options...
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