73-87chevytrucks.com

73-87 Chevy _ GMC Trucks => Electrical => Topic started by: 80HD on December 06, 2018, 12:50:51 AM

Title: Dead Short with IGN off
Post by: 80HD on December 06, 2018, 12:50:51 AM
Hi All,
79  GMC C1500, twin tanks, BBC, A/C, Rebuilt motor w/700R4. 
With Ign off, every fuse and lead pulled from the fuse box under the driver's side of the dash, I have a pulsating current with a test light between neg batt cable and neg batt post.  Any thoughts would be appreciated.  Pulled the alternator plug and the A/C clutch plug, still pulsating test light.  This short will run the battery down in two days. The 700R4 has lead connected to power. If the lockup wire was hot with the key off, could it pulsate?
I can't think of anything that pulsates. Electrical crap makes my butt chew gum!
Thanks in advance,
Kim
Title: Re: Dead Short with IGN off
Post by: MIKE S on December 06, 2018, 10:12:38 AM
You need to pull the main charge wire off the back of the alternator to eliminate that as a cause.
Title: Re: Dead Short with IGN off
Post by: 80HD on December 06, 2018, 10:24:19 AM
Thanks for responding, I disconnected the alt completely.  Light is still flashing, no brighter, no dimmer.
Title: Re: Dead Short with IGN off
Post by: 80HD on December 06, 2018, 10:25:51 AM
https://youtu.be/zz6KXb_t-CE (https://youtu.be/zz6KXb_t-CE)
Title: Re: Dead Short with IGN off
Post by: MIKE S on December 06, 2018, 12:29:50 PM
Try disconnecting the plug on the driver side of transmission and see if that's it.
Title: Re: Dead Short with IGN off
Post by: 80HD on December 06, 2018, 01:36:07 PM
I sure wanted you to be right but no dice. I'm starting to think it's related to the starter.  The starter is the only thing directly connected to the battery. Am I missing something else connected full time hot to the battery?  Can a solenoid do this?   
Title: Re: Dead Short with IGN off
Post by: Irish_Alley on December 06, 2018, 03:16:06 PM
you could remove the power wire going from the starter to the cab leaving only the main wire going from the starter to the B+ and see what that does. if it still pulsates it would have to be in the starter, but i dont really see what in the starter would do this. but again i dont really see what at all in out trucks would do this. did you put a multimeter on the battery just to see what the volts drop to or even if you can see it?
Title: Re: Dead Short with IGN off
Post by: 80HD on December 06, 2018, 04:39:52 PM
Hi Irish,
I did put a DMM on the batt to determine the voltage(drop or pulse) and the voltage hasn't dropped but a .1-.2 of a volt the 2-3 hrs. I was farting with it.  The batt is 4 mos. old. BTW

I'm not sure I'm good enough to get a wire off the starter without removing it.  That will be another day.

The truck is going into the tranny shop tomorrow. The 700R4 is due for a much needed overhaul and buildup. The motor can power through 3rd gear at will!

Thank you all for the responses, I'll get back on it when it returns home.
Title: Re: Dead Short with IGN off
Post by: bd on December 06, 2018, 07:43:33 PM
The link to YouTube is unavailable for viewing.
Title: Re: Dead Short with IGN off
Post by: MIKE S on December 06, 2018, 09:51:11 PM
Aftermarket sound system? Alarm? Anything under dash that has tapped into a wire. Headlight switch should be live even with fuses pulled. It has a built in circuit breaker. High speed A/C relay doesn’t have a fuse in fuse box. I think horn relay is also powered. Pull connectors to these one at a time.
Title: Re: Dead Short with IGN off
Post by: 80HD on December 13, 2018, 09:51:54 AM
Thank you one and all!  FOUND IT!!  It indeed was the aftermarket radio.  The "audio pro" that installed it spliced into a non keyed hot wire. Pulled the inline fuse and no more draw.

Again Thanks so much for the help!