Does anyone know what this black box is? Under the radio

 

My guess is some sort of alarm. looks like a sensitivity adj. on the front. If it were a factory unit it'd plug into the harness with a legit connector. Pull it out and look for some sort of ID number or symbol.
Removing and repairing wiring might solve your MIL in the process if it's aftermarket. I'm pretty confident it is. . Factory alarm kits weren't as refined as they are today, but in-line fuses, solid color wiring still was a red flag, even back then.

 

Gotcha alright. It does have a viper system on it.

 

If that was my rig, that Viper would have been gone already. Pulling miles of aftermarket wiring and soldering the violated factory wire back together will be very rewarding to the soul.

 

Ok gentlemen. Finally pulled the tank down today because I narrowed it down to fuel pressure and low and behold the hose coming off the pump and a loose clamp and worked it’s way off just enough to let some fuel through but not enough too run and drive. Thank you for all your help!

 

Nice!!

 

Thanks for posting your solution!