No start, no crank, no dash lights after battery disconnected

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JohnDenver

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Check battery connections, mine has an extra ground to body right there at the battery so make sure you got all the grounds. Aftermarket anti-theft is always cause for concern. Check voltage at battery with multimeter.

From the symptoms, if sure sounds like either a weak battery or a poor ground.

Did some shopping, got a cheaper Klein multimeter and checked the battery—very, very low, max reading was 4V. I was puzzled since I had it disconnected I didn’t think it would have dropped since it started fine before. I remembered my timeline was the blower quit working and I burned up the wire connector to it. Then I ordered parts with battery connected, then a few days after parts came in I disconnected it and started working. So may have been 10 days connected then about a week disconnected. It’s winter though not extremely cold right now in my part of CO but couldn’t help, and maybe I had some amount of draw on it. Today I invested in a charger so I have it trickle charging now. It’s a dual purpose starting/deep cycle AGM that should be tolerant of being drawn down low.

Now that I finally got a meter, I should be able to check the simple stuff first Thanks for the help! Fingers crossed the blower works when this step is done.
 

Trio

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Did some shopping, got a cheaper Klein multimeter and checked the battery—very, very low, max reading was 4V...

Now that I finally got a meter, I should be able to check the simple stuff first Thanks for the help! Fingers crossed the blower works when this step is done.

4 volts is D-E-A-D. I wouldn't trust a battery that had cycled that low, but to your point, maybe your AGM can tolerate it. Let us know the outcome once you have it charged.
 

Komet

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Looks like the multimeter is already delivering some results. You can check parasitic amp draw by installing the multimeter in series with the positive cable and putting it in 10a mode. Watch out, testing amps is potentially dangerous to your meter, sometimes you have to put the probe ends in different spots to make sure you've got 10a of protection depending on the meter so read your manual. If you have more than 10a parasitic draw (very serious draw, uncommon) it'll blow the fuse in the multimeter.
 

JohnDenver

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4 volts is D-E-A-D. I wouldn't trust a battery that had cycled that low, but to your point, maybe your AGM can tolerate it. Let us know the outcome once you have it charged.

Turns out not long after my post the charger just said battery failure. I took it into Batteries Plus where I bought it to see about a warranty replacement since it has years of warranty left. They have a better charging system and will see how that goes, but it may be up to 24 hr of charge time so may not hear back till Wednesday. Hopefully it recovers or warranty covers it. I’m always skeptical of warranties actually working for these kinds of things since there is usually some way to blame the user.
 

JohnDenver

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I’ll bet if it doesn’t recover your getting a new battery.
4 volts is D-E-A-D. I wouldn't trust a battery that had cycled that low, but to your point, maybe your AGM can tolerate it. Let us know the outcome once you have it charged.

Well, battery was dead and it was replaced under warranty. Unfortunate to have it not last long and annoying to track down, but beats paying for it. Truck starts now and my blower works again so that project appears to be a very slow success.

Thanks for the help!
 

someotherguy

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Glad you got it figured - we don't expect batteries to croak like that but sometimes they do.

To answer some of your earlier questions, that is absolutely not how Passlock behaves, for future reference. Passlock will allow the engine to crank normally and start, but for just a moment, then it will stall.

Your '98 has Passlock; all '98 year model GMT400's have it (and all the years afterwards through the very last of the GMT400 line, which believe it or not continued in the U.S. until '02 at least with the 3500HD.)

I don't recognize that box you're holding in the pic, it's definitely not factory, and you're probably correct that it is related to your aftermarket antitheft system. If it's still working you could probably leave it alone. If you want to remove it, dedicate some time when you can afford for the truck to be down in case you run into issues tracing the wires to put them back to factory configuration so the truck will start again once it's removed.

Richard
 
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