Thank you so much for the help. Sorry for the delay in my responses, just like everyone else work and life are getting in my way of troubleshooting this problem. I am really struggling with this because it is not repeatable. I have it all hooked back up and it not pulling the battery down instantly, but still loses all power when key is turned on.
I think I may need to just start over. I checked on it before work this morning and the battery was down to 11.5V (must have a draw). Currently I am charging the battery again. Everything is in place, all fuses and battery terminals. When I get home tonight I will put the amp meter in line and wait 15 min to see what the true draw is.

Thanx again for the help and patience.
Karl

 

Like I said I am starting over. I load tested the battery - good. Put amp meter in line, waited for computers to go to sleep, parasitic draw is now .03A. All seems good to me. The problem now is as soon as I turn the key power is drawn down and nothing works.
I would like to develop a good plan as to how to continue from here.

Thanx,
Karl

 

We need to determine:

That the battery can charge and hold to 12.6V
That the battery can hold the proper voltage under a calibrated high current load and then recover:

https://www.liveabout.com/vehicle-ba...esting-4083840

Which circuit leg produces the excessive current draw at key on
Which load in that circuit has malfunctioned


How much voltage could the battery hold during the load test. Do you know the current draw (load)?

Was the battery charged back up to 12.6V after the load test?

What does the battery voltage drop to during key on? What is the current draw on the main battery cable?

Which fuse do you have to pull to get the current to drop to normal at key on, is it still the TBC fuse? If so, what is that fuse value?

You mentioned once that disconnecting the starter stopped the high current draw, is that still the case?

Make sure that when you disconnect a fuse or cable that you recycle the ignition switch, turn it back on and recheck the current to check that you have found the offending circuit. The high current may just simply time out while your working on the truck, especially given that the TBC circuit powers the BCM.


George

 

Sorry for delay was waiting for a amp clamp to arrive.

How much voltage could the battery hold during the load test. 12V Do you know the current draw (load)? Fixed load current 100A w/ Neiko 40510A

Was the battery charged back up to 12.6V after the load test? Yes

What does the battery voltage drop to during key on? 5.2V What is the current draw on the main battery cable? 4A with key on

Which fuse do you have to pull to get the current to drop to normal at key on, is it still the TBC fuse? If so, what is that fuse value? None of the fuses will drop the current

You mentioned once that disconnecting the starter stopped the high current draw, is that still the case? No

Thanx,
Karl

 

The load tester draws 100A and the voltage drops to 12v (which is a good thing) but yet in the vehicle at key on the voltage drops to 5.2V and the system is drawing only 4A? Something does not square. Even when cranking you draw around the same current as the load tester but you are only In run with 4A. For a battery to drop to 5V at 4A it would have to be defective with at least one shorted cell but yet this battery charges properly and load tests properly.

Are you measuring the voltage at the battery terminals on DCV?

How are you measuring the current and on what cable? Is the meter on DCA?

Is there only one positive and negative battery cable or have other wires been added?


George

 

Are you measuring the voltage at the battery terminals on DCV? Yes

How are you measuring the current and on what cable? Is the meter on DCA? I have tried the positive cable at the battery, there are two cables (a black and a red) I am around both of them. I have also gone to the cable that runs to the fuse box with the same results (varies a little between 4 and 6 DCA.

Is there only one positive and negative battery cable or have other wires been added? Everything is stock. Negative has three wires and positive has two.

 

Test the black and red positive cables separately.

George

 

6.5 red 5.5 black

 

Amps or milliamps? Those are two separate circuits so that would be 12A in total draw on the battery. I want to try something different. When you are in run and there is 6 amps in the black wire, measure the voltage at the crank fuse. It should be zero but I bet there is voltage there. Then pull that fuse and see what happens to the current in the black wire. If no change, pull the starter relay and repeat

George

 

Now I have 6 DCA on red and nothing on the black.