Wiring issues on a 1994 Chevy Conversion

[Walter Buller]

We have completed the installation of the "93 Cummins 12v motor and "98 NV4500 trans. into the "94 Chevy dually. Everything is working great except the lights. When the headlights are on the turn signals don't work. They work fine with the headlights off. Also, even though we installed auxillary temp, oil pressure and alternator gauges, the original alternator and temp. gauges in the dash continue to work, but they stop working when the headlights are on. Same thing with the fuel gauge. We ran a separate wire from the headlights to a new switch we mounted on the dash to isolate the headlights from the rest of the wiring but it made no difference. Of course we can't get a safety inspection sticker until at least the lights are working properly. I would sure appreciate some feedback from any of you that might know what the heck the problem is or at least how to get around it.
 

[504]

I am guessing you lost the ground somewhere. Maybe engine to frame strap. I think there is a body, to battery ground cable too.
 

[Bob]

Yes, he's lost a ground somewhere.

Try running some temporary ground wires between the battery negative posts and the frame, the radiator support, the fenders, and the cab, and note when the problem goes away, then install a heavy replacement ground strap or wire between the affected components, or (at the very least) find the factory ground that was left unconnected.

Could possibly be a black wire or a group of black wires with fairly large eyelets at the end that was left hanging by the battery(s), or the radiator support, or that sticks out of the engine harness and went to the engine block.
 

[VicS]

I agree bad or no ground
 

[Walter Buller]

Thanks guys. I suspected as much, but nothing changed after we ran one additional ground wire. We'll run some others as ya'll suggested and see what happens.