batteries discharged very quickly and truck is dead

Been having an issue with the battery light coming on dimly and intermittently but the truck has been starting just fine. Started it up this morning no issue, stopped for a coffee and came out no start batteries low and clicking at solenoid when trying to start, boost the truck and head home, on the way home volt meter drops down to 8 volts, gauges go nuts and it dies as I enter the laneway. I'm guessing alternator? Going to charge the batteries in the morning and see what the alternator is putting out but it sure drained the batteries quick on the way home! Any similar experiences out there?

My guess is that it drained the batteries on the way to coffee and the drive home finished it off. Sounds like the alternator is going out or gone to me. I'd get it load checked just to be sure.

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Yeah, Sounds like alternator.
But look at it. Could be a bad connection.

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Sounds like your alternator is shorting to ground. I just replaced mine for this very reason.
Came home from work with no issues and shut the truck off. Went to start it in the morning and dead. Took my volt meter and measured 3Vdc on each battery.
I disconnected both batteries and charged them. When I reconnected the first battery it drew an arc, to big to just be the security system etc. I measured that battery while it was connected and the voltage was already at 7 volts and the cables were hot. I disconnected the battery and put the meter to ohms and measured a short, very low resistance between the two battery CABLES (positive and negetive).
I disconnected the output lead from the first alternator and made the same measurement. I then disconnected the output lead from the second alternator and measured around a mega ohm. I put the meter leads on the output stud of the second alternator and the case of that alternator and read a short, very low resistance.
Swapped out that alternator and all was well again.

quick update, charged the batteries for about an hour with a little charger and it started right up spun over quick and lit right off, glow plug relays did their thing. Threw a volt meter on the batteries and was reading about 13.5-13.7. At this point the battery light was not on in the dash, took it for a drive and as the rpm approached 1800-2000 the light started to flicker and on the way back was on pretty much solid. pulled in the drive left it running and the volt mere was reading about 12.6-12.8 and was slowly rising, headlights were on heater etc to load the system. eventually it made it's way above 13V but the battery light was still on in the dash. I'm guessing this alternator or possibly the regulator is done and can't handle much of anything of a load. I did disconnect the batteries and load tested them individually and they seem to hold a load okay, connections are tight and clean.

You can read the output voltage right at the alternator.

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Those readings were at the batteries and the stud on the back of the alternator.

new alternator on and it's all good, showing 14.4 at the batteries and 14.5 at the stud on the back of the alternator.

There you go. Looks good!

Thank you for posting the end results! So many threads I read never say what the fix was.
Glad you are up and running again.