Thanks for the input, the 10a fuse on the relay was blown.

Now, any ideas what would blow that fuse normally? Will it go again or is this something that happens rarely and usually doesn't re-occur?

I see a zener diode in the relay, perhaps a load-dump from the alternator shutting off did the nasty task? Must be there to protect against something.

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Gone to the dark side

- Jeff

Check to see that the battery negative lead is not loose or corroded. The purpose of the thing is to detect over voltage or surges. A bad altenator regulator could be involved too
I suppose a bad battery could also trigger a fuse to blow. Fuses also fail from fatigue, that is due to many on off cucles at a current near the high end of their operating range, commn problem in GP strip fuses. Was your fuse really Blown or maybe just fatigued?

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!