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73-87 Chevy _ GMC Trucks => Electrical => Topic started by: slideways on May 11, 2021, 07:25:05 pm

Title: Truck only starts when grounded to engine
Post by: slideways on May 11, 2021, 07:25:05 pm

 83 K10 that i'm doing a ground up on. Truck functioned fine when taken apart. I labeled all connections and where they went. Months ago when i started reassembly i had the cab on 2x4's not bolted down. I have been successfully starting/idling the motor with the braided strap on the little firewall stud, starter hot all normal but the ground cable from the battery would only crank the truck if i put the end on the alternator bracket/other engine component. It would power up but not crank if i put the end of the cable on the PS frame rail like it was originally located.

I now have the cab bolted to the frame correctly which i thought would complete any grounds needed from cab to chassis.Today i got curious and cleaned up the frame and bolted the negative cable there. Truck powered up and barely cranked.. braided firewall ground started smoking. The only other wire that isnt connected is the rad support ground wire. I figured i didnt need that except for headlights etc. I am horrible at wiring so i tried to label everything very clearly and take pictures of exactly where it came from. This has me a bit stumped.

Title: Re: Truck only starts when grounded to engine
Post by: VileZambonie on May 11, 2021, 07:35:26 pm

You need to have the negative cable directly attached to the engine block or the alternator bracket (uglier and more resistance this way though).

Title: Re: Truck only starts when grounded to engine
Post by: slideways on May 11, 2021, 08:16:03 pm

But before it was just bolted right to the top side of the frame rail sandwiched with the ground that goes to the core support. What would have caused the truck to run ok at that point?

Title: Re: Truck only starts when grounded to engine
Post by: bd on May 11, 2021, 08:34:12 pm

Luck!

Title: Re: Truck only starts when grounded to engine
Post by: slideways on May 11, 2021, 08:41:10 pm

Lol sounds good guys. So just clarify me a list of what i should have attached to where here... The negative cable to the block or other engine mount. The thin braided firewall to rear of head strap, and the core support to negative terminal wire. Anything else?

Title: Re: Truck only starts when grounded to engine
Post by: bd on May 11, 2021, 08:53:32 pm

See Basics: Vehicle Ground (http://forum.73-87chevytrucks.com/smforum/index.php?topic=35756.msg301879#msg301879).

Scroll down to STANDARD INVENTORY OF 1973 - 1987 (91) C/K/R/V LIGHT-DUTY TRUCK GROUNDS.