I dont use forums much but I need help. Month ago I got into a fender bender and had to rebuild the front end of the truck. It came out great. But now I have another issues the previous owner used a plow harness to jerry rig the head light harness and I wanted to delete that. So its now the original headlight harness. All the grounds that were along the rad support are back on and the harness is oem but last night when I fired the truck up it ran great and I wanted to test the lights. Driver side light was out and the bulb is new. The high beam indicator was on along with the right hand turn signal. As soon as I pull the headlight switch out to engage the lights the truck bogged out and almost shut off. But she stayed running. I used the left turn signal and it worked. Used right hand the truck shut off. Now the truck dont even start. I put a new coil on it and im still not getting spark. Now previously the fuel pump would prime the system when I turn the key on and it would shut off. Now when I have the key on the pump continues to run. Im honestly stumped. Please help!

 

Usually a running pump with no start means a bad ECU/computer, likely the capacitors.

Cant rule out the wiring though since it was just messed with.

 

i believe you can buy a new upgraded headlight wiring harness from jeff bronco graveyard. Making sure all the grounds are in place is huge. Also the headlight switch itself on our rigs are known to fail, replacing that isnt hard for the most part, i would also advise replacing the plug for that headlight switch.

Headlight Switch and Harness Connector Replacement - FSB Forums

 

Sounds like someone may have wired the ignition in with the lights on the same circuit. Or a bad ground circuit at the battery.

 

Normally I would agree with the above...but we recently ran into this same scenario in the OBS forum, turned out to be missing grounds on the radiator support. 3 to be exact, but not sure which ones. First time I ever ran across a missing ground to trigger the pumps to run continuously.

 

That is odd isn't it... Had no idea there were THREE up there!