2000 GMC K2500 - parasite draw

Dang truck has a parasite draw of about 700 MA and kills both batteries in a few days .
Checked early spring and alternator showed a bad diode so replaced the full unit . 
Then find out it still kills batteries . 
Next the fuse blew to ECM somehow and no power to fire plugs and no fuel pressure .
Had local shop replace fuel pump and install new straps on fuel tank as old ones were rusted to scrap . 
 Needed to truck to plow a week or so back - all the time i was plowing the headlight alarm sounded they were on / key in ignition ding .
 Now as has auto on headlight switch since I got the truck in 2000 I have always just left switch in auto position . Turning it to off alarm still sounds until key is removed completely from column.
  About ready to look for another truck as body rusting out , frame rusty , front differential brace to frame rusted off frame, tale gate rusted , hinge points rusted off box , bed rust through in many spots  . 90,000 miles and wonder if it's worth dealing with .
  What is a real mark of quality is front bumper has holes rusted through it i several places . ONE OF GM good ideas .
  I found out when ordering part when I rebuilt the transfer case , GM put 3/4 running gear under a 1/2 ton frame then spacers under cab to raise it up higher and called it a 3/4 ton 

Coke I just traded one of those off. A light duty 3/4 ton.
Mine had a little over 600000 miles on it. Wore out from front to rear but was a very good truck.
Was starting to have wiring issues as well.

I know this is not solution but may help in the short term. Install a master disconnect at the battery. Shut it off when you think it will be parked for day or two. It's not a bad idea on any vehicle. Have you checked both batteries to see if they are good? Looks as if you have done some pretty careful diagnostics. 

Edited by Ed (Ont) - 11 Jan 2025 at 8:32am

I had a 99 GMC 2500. Loved it. Did a great job for me and just sold it a couple years ago. Still miss that truck. One problem these had was the fuse panel under hood would turn green underneath. Lift it up and check it. Was a common problem on those years of trucks and vans. My buddy that is a mechanic at a GM dealership clued me in on that one. GM still had those available in parts a few years ago and the price was very reasonable. 

All started a year back , replaced alternator and main battery . Still killed batteries , left trickle charger / maintainer hooked up and could still drive it when needed . 
 Someone unplugged charger , stoned plow battery dead , main battery came back to life , then went dead again and no start , when found the ECM fuse blown and figured fuel pump in tank was bad (corrosion on wires on pump in tank). So now 2 new batteries and sat for 3 days in the extreme cold and both batteries froze - after 3 days in heated shop and trickle charge got them back to 12.9 Volts 
 The indicator light for the shift position in dash does not light up so now guess what gear your in . Next was the ding / ding when driving with headlights on ....
  Heck my 76 GMC dump truck or the 66 White dump truck electrical are easy and can be fixed with no problem - but this has got me ready to have a fire sale .

Edited by Coke-in-MN - 11 Jan 2025 at 1:30pm

most economical solution is to put ammeter in and pull fuse to locate WHERE the drain is coming from. This costs you nothing, 400A disconnect is a few bucks( oops .need 2, two batteries....)_I'm assuming batteries are NOT in parallel, have an 'isolator' between them ?

MY 2004 chevy had a bad radio and was running the battery dead after 2 days.