Where does the Radio ground out?

[AaronB31]

I've got an 89 Mighty.

I've got an aftermarket radio installed with an adapter to the factory harness, and a tachometer whish seems to be tapped into the same harness (both installed by previous owner). Recently both the tach and radio have started turning themselves on and off while I'm driving.

The battery and alternator tested good at O'Reillys, and I replaced the entire ground cable coming from the batter because it was old and looked sketchy. The truck starts up and runs just great, but the tach and radio continue to turn themselves on and off constantly. I feel like it's a bad ground, so I checked and redid every ground location I could find with the dashboard taken out, and no luck so far.

Does anyone know where the radio grounds out on the factory harness?

I'm open to ideas if anyone else thinks they know what my problem is.

[Jeff V.]

The factory radio grounds through its metal casing and eventually, the frame. Most, if not all, Mitsu factory radios work this way.

There should be a wire coming from the radio shell or the mounting bracket, and it should be screwed to the frame somewhere behind the dash.