Electrical problem
1996 Ford Ranger 4 cyl Two Wheel Drive Manual
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I have a 1996 Ford Ranger with an electrical problem. When driving the truck if anything is turned on (stereo, heat/a.c., headlights, wipers), the speedometer stops working. When the other things are turned off, it starts working again. I have changed all the applicable fuses. Is it just a wiring issue? And if so, how do I go about finding where the wiring issue is? Thanks.

Have you added any aftermarket electrical equipment to the truck? Stereo, speakers?

If not, get a Haynes manual and make sure it has the speedometer (IP) schematic and trace the wiring from IP to trans sender, looking for insulation breaches, heat related insulation marks (burns).

it has an aftermarket stereo that's been in the truck as long as we've owned it (since 2002). It's never given us any trouble like this before, though. Could the stereo have something to do with it?

At least check the connections to the stereo, they may have worked loose and some connections to the stero are hot all the time.