Well, here's the symptom. A while back my parents went to move my truck and it wouldn't start. No juice, nothing. They had driven it about an hour before and it ran fine, but then nothing. Well, I just got home and looked it over, and here's whats up. I tried to jump it off and what happens is, I turn the key to the run position, the volt meter jumps up to normal, then the lights dim and it goes to just above the bottom of the gauge within about half a second of turning the key. After that, no matter how long the key is on, it won't go back up to normal. My first thought is either a short or a broken battery (I have bounced it around off road pretty hard before). I thought maybe this is a common problem so has anyone seen this before? Thanks

 

Low voltage with key on sounds like the normal glow plug cycle. Turn key to "run", glow plugs come on, voltage drops. As far as I can recollect, I've never seen the glow plugs go off and voltage come back to normal without starting the truck. I assume they eventually will, but I've always either started or turned the key off. A minute or so after starting, the glow plugs go off, and voltage goes back to normal. But if it doesn't start, I don't know how long, before the glow plugs cycle off; it might be a minute or two. Except for not starting, what you're seeing sounds normal.

From experience, the truck will run a LONG time on just the batteries, with no obvious symptoms until the batteries are just about dead or won't start the truck.

Your immediate issue may be not enough voltage left in the batteries to feed the glow plugs and starter, even after a quick jump. Since the glow plugs draw quite a bit of current, you may need to charge the batteries for a while to get enough voltage to feed both glow plugs and starter. If you're jumping, leave the other car running and cables hooked up for 10 minutes or so before trying to start the truck, and preferably keep everything hooked up until you're started. Wait until the wait-to-start light goes off before cranking. If you've got a 110 v charger, leave it hooked up for as long as you've got.

The batteries have large capacity, and if they've been really run down, it takes quite a while to get useful voltage (ie, enough to heat glow plugs and crank the starter) back into them. Once you've got it running, get it back home, put a charger on overnight, and then diagnose the charging system and batteries.

My $0.02. Other folks likely have more comprehensive advice.

 

I use my glow plugs for the first start of the day and then turn them off for the rest of the day. I put a switch on the live wire at the relay and a toggle switch inside. If I was having your problem, I would switch off my glow plugs and see how it acts. I suppose you could unhook the live wire from the relay and then turn your key on to see if the voltage drops down, it shouldn't. If it does then I would guess a bad battery or two.