Hi Mark,
I love the old square body Dakota. I owned about 5 of them over the years. Now I have the new body style, and they are not the same trucks.
Anyway, I have no idea what the person before you has done, but something seems off.
If you look at the first two pictures below, they show the power distribution. The remaining one are of the fuse box. See if anything there makes sense to what you experience.
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Next, the last picture below is of the headlamp switch. Check to see if there is power to the wire I indicated.
Let me know.
Joe
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Thursday, April 30th, 2020 AT 8:03 PM