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I'm actually surprised that this hasn't come up before. I've seen it a bunch locally.
The brake light circuits and tail light circuits all go thru the Mulit-function (MF) switch. It's got a very complex set of contacts that have to line up exactly right or something just won't work. The button for the Hazard flashers is on the top of the steering shaft cowling. Any dirt, coffee, Diet Coke, dust from the powdered donuts or anything else that might get loose inside the car always seems to get funneled right down this open switch port and right into the contacts of the MF switch and screws everything up.
The easiest thing to do is to shower the Hazard button with WD-40 and work the button in and out as many times as you can stand (50-60 cycles usually does the trick). This gets the WD-40 into the MF switch and cleans the contacts of the switch. This usually gets everything working again.
I've seen it all. Lights that stay on, lights that don't work, one brake light on and the other doesn't work...any combination of wild-ass light function is usually caused by dirty contact in the MF switch. That's why I abbreviate the name as it has so many other appropriate connotations.
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