Author Topic: constant short  (Read 248 times)

Offline gwcrim

  • Registered Users
  • *
  • Posts: 137
  • Far from a Newbie
constant short
« on: November 07, 2019, 12:44:25 PM »
My '80 C10 has an electrical issue.  The battery is under constant load even with the ignition switch off.  I've pulled every thing out of the fuse panel, relays included.  I unhooked the ciggy lighter and the alternator.  There's still al current draw.

What is powered prior to the ignition switch?  Headlights, horn....?  I need direction.

Offline JohnnyPopper

  • Junior Member
  • ***
  • Posts: 516
  • Newbie
Re: constant short
« Reply #1 on: November 07, 2019, 02:54:43 PM »
So I assume you end up with a dead battery?

Have you used a meter to measure if there is amp draw?

It may be your battery is the prob?
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline gwcrim

  • Registered Users
  • *
  • Posts: 137
  • Far from a Newbie
Re: constant short
« Reply #2 on: November 07, 2019, 03:50:54 PM »
Right now, I'll I have is a basic multi-meter.  The battery cable is removed and there's a 12V current running through.  If I leave the battery attached, it goes dead.  If I unhook it, it's good whenever I start it again.  Days, weeks....

Offline VileZambonie

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 17393
Re: constant short
« Reply #3 on: November 07, 2019, 04:00:18 PM »
Quote
The battery cable is removed and there's a 12V current running through.

What?

How are you checking for your parasitic draw?
,                           ___ 
                         /  _ _ _\_
              ⌠ŻŻŻŻŻ'   [☼===☼]
              `()_);-;()_)--o--)_)

Offline gwcrim

  • Registered Users
  • *
  • Posts: 137
  • Far from a Newbie
Re: constant short
« Reply #4 on: November 07, 2019, 04:52:19 PM »
Just seeing if there's any voltage going through when everything is shut off.  Positive lead on the positive terminal.  Negative lead on the positive cable.

Online bd

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 5350
Re: constant short
« Reply #5 on: November 07, 2019, 06:20:07 PM »
Voltmeters have high internal resistance.  Inserting a voltmeter in series with the battery cable is totally invalid and useless as a test!  Use an ammeter with an inline fuse that is rated at the ammeter's full-scale reading.  If you have an ammeter capable of measuring 10 amperes, insert a 10-amp fuse in series with either ammeter lead and the battery cable. 

If you don't have an ammeter, substitute an incandescent test light for the ammeter.  If the test light illuminates the same brightness when connected in series with the battery cable as it does when you place the test light directly across the battery terminals, then there is enough of a parasitic draw to pursue and diagnose.  Otherwise, the draw is inconsequential (less than ~45 ma).  Be sure that all of the doors and glovebox are closed and that all lights and electrical appliances are switched off then you perform tests for parasitic draw.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline gwcrim

  • Registered Users
  • *
  • Posts: 137
  • Far from a Newbie
Re: constant short
« Reply #6 on: November 07, 2019, 07:02:03 PM »
I have a "DC A 250m" setting on the MM.  250 milliamps?

Online bd

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 5350
Re: constant short
« Reply #7 on: November 07, 2019, 07:35:19 PM »
I have a "DC A 250m" setting on the MM.  250 milliamps?

Yup!  Under the circumstances, it's probably better to use an incandescent test light for a grassroots quick test and flip for a better DMM.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline gwcrim

  • Registered Users
  • *
  • Posts: 137
  • Far from a Newbie
Re: constant short
« Reply #8 on: November 09, 2019, 07:54:43 AM »
Thank you very much.  I had an amplifier plugged into a 'battery' feed.  Unswitched.

Offline JohnnyPopper

  • Junior Member
  • ***
  • Posts: 516
  • Newbie
Re: constant short
« Reply #9 on: November 10, 2019, 10:50:39 AM »
Good catch!

Use a relay to take it on/off line.
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction