Sorry for another thread but I believe I exhausted the amp drain search and learned some things in the process.

OK, starting from scratch:
1999 ½ F250 7.3L Crew/Longbed manual locks/windows
2x New Batteries a few days ago, same symptoms as old batteries (oops)

Sitting overnight loses .1 volt due to cooler temps in am measurement:
9pm 12.92v
7am 12.83v
11am 12.93v*
*won't start

The amp draw measured at 9pm and 11am is essentially zero (reading .06 or less, usually 0.00) on both cables exiting the passenger side battery. This is sitting for an hour plus with the hood courtesy bulb removed. (although it drops to near zero within a few minutes of the domes going off). Using a clamp around ammeter.

The alternator is charging (14+v reading while driving)

When trickle charged overnight the truck starts fine. Plugging in the block heater makes no difference in starting (or not). 45ºF overnight

When it doesn't start:
-double keying the glow plug light comes on
-tach needle bounces on crank
-voltage of 12.8 drops to 11.2 on glow plugs, then 10, then 7 while cranking
-sounds like it's almost going to catch, then bogs hard and the voltage really drops

Again, it starts fine when charged and starts after short trips (by virtue of my wife having made it home). Haven't tried to jump start as I don't have anything handy that is boss enough to jump one of these.

Typical use during failure:
Charging with charger
Start
30 min to store
3 stores, start 3 times
30 min to home
Sit overnight
Won't start

This morning I checked that the battery terminals and battery clamps all had the exact same voltage. There are occasionally amps between the batteries (.37 to .08) measured on each end of the cable going over the radiator.

So, if there is no drain and the block heater doesn't help, but it starts fine if it hasn't been driven/sitting, what is next to check?

 

All ground cables to and from the engine block and frame. Make sure they're tight and clean. Then I'd look at the starter drawing excessive current.

 

If your large battery cable system has a "tee" type connection on one of the large + cable connections, then I believe you are going to have to disconnect one battery completely and lay the cables on rags(so they don't short out) before you can get a good amp draw reading. I would be curious what amp draw you get if you did this.

I you could also figure out which one of the smaller wires actually feeds the elec system of the truck, you could take a ammeter reading one that. There is probably a group of them though.

 

Disconnected the driver side + first, measured everything got no draw.

Put that back and removed the passenger side + and for a short bit I got .15 on the C & D points, but that went to near zero.

Driver's side is 13v disconnected, pass is 13.2v disconnected (it's been on the trickle charger)

I'm leaving the passenger battery + disconnected with no charger to see if one drops more than the other. I'm also planning to leave it sit without driving to see if the system goes down (barring better course)

Dumb question, is the over radiator positive cable only between the batteries? I might just take that apart and visually inspect it because I seem to get weird variations between C & D (not sure if it's me being sloppy, batteries balancing one another or what)

 

Ok, what I would do next is get it going, drive it like you normally would during the day, get home, and then take both battery + cables off the batteries and let it sit overnight. The next morning, go out, put both battery cables back on, and then try to start it. I am not convinced fully that it's a drain problem, but this would verify that correct? You are not getting any bad drain readings, and the engine starts when warm, not when cold. Just another test to verify what's going on.

 

I think I may have figured out why I can't find an amp drain. Apparently my wife has been having to stomp on the gas pedal while cranking to start the truck and didn't bother to tell me. Well I finally was there when she was starting it. On the second try she stomped the gas pedal while cranking and it fired right up.

I'm guessing that's not electrical after all.