Hey fellas

 

Started diag on a battery drain today.

Seems when I disconnect the alternator the drain goes from 480mA to under 50mA ........ how do I determine if I have a bad ground on alternator an open circuit ..... or just a bad alternator.

 

John, maybe I misunderstood what you meant. I thought you said that if you pulled all the wires from the 140A fuse and still had a draw at the fuse, but now I am re-thinking that. I agree with Mike. Pull fuses and check each spot for the draw.

Pulled every single fuse except the yellow safety tab airbag ones .......  no change.

Only one that had any effect was the 50A battery fuse in top left corner ..... but guessing thats expected.

Then what is bypassing the fuse block but is powered by the battery?  What is wired onto the positive stud? I know you don't have any programmers with the P pump, but you have an electric fuel pump? You've eliminated everything you pulled the fuse for, so the list should be getting shorter.  

 

Unfortunately, you don't know for sure what all the wiring is on your new truck... so it could be several things from Gauge power to a relay for the fuel system.  It should be easily enough tracked down though. Just keep following the amperage draw with your multimeter in the same way as the fuses.  Test by unplugging if that is easy, or by checking for a draw with your meter. 

Edited November 30, 201410 yr by CSM

There's lots on the positive terminal. But I'm bypassing that by removing the positive connection out of the way .... and the draw comes from the 140a main red wire ..... so at that point none of the accessories are connected .... correct ?

You can see what I'm doing here.

All accessories are tied to red battery cable which is not connected to battery.

When I probe from battery to the 140a studs with ALL alternator and FSS wires removed ( so only studs showing i remove those 4 wires in pic) I still get 0.5a draw.

Removing fuses made no difference. Both in PDC and in cab.

Edited November 30, 201410 yr by JOHNFAK

Huh.  So the probe is going from the positive bat terminal to the 140A stud... and you are reading 0.5A.   

 

 

I am 99% sure that the positive lead that you have disconnected powers the 140A stud.  You can check... (also check if the disconnected lead has 12-14v on it from the pass side... I don't think it does, but it might skew your results if it is connected to that battery.)  

 

So, if the 140A stud is powered through the disconnected lead in the picture, you still can have a leak from the wires connected to the lead.  

Huh.  So the probe is going from the positive bat terminal to the 140A stud... and you are reading 0.5A.   

 

 

I am 99% sure that the positive lead that you have disconnected powers the 140A stud.  You can check... (also check if the disconnected lead has 12-14v on it from the pass side... I don't think it does, but it might skew your results if it is connected to that battery.)  

 

So, if the 140A stud is powered through the disconnected lead in the picture, you still can have a leak from the wires connected to the lead.  

 

Yup - but I disconnect that red lead (connecting the 140a to the battery). So its two bare studs ........ and I probe from battery (+ve direct to the stud) and still read 0.5A

And you couldn't isolate it by pulling fues on the block there?  Weird.  well... it has to be there somewhere. You could try just probing from teh battery to the top of each fuse.  There is a small gap there a sharp probe should touch metal, so you shouldn't have to pull any.  You could even check the bags. 

All the big fuses are encased in plastic so there is no way to probe them. But still in all you are measuring amp draw so you have to break the circuit to measure amp draw.

Where does the black wire (looks like maybe two black wires) go? Have you pulled the nut on the fuse and checked just that wire? If you  pulled all the fuses the small black wire has been in the circuit for every test (doesn't look like any wrench marks on the nut)>

Where does the black wire (looks like maybe two black wires) go? Have you pulled the nut on the fuse and checked just that wire? If you  pulled all the fuses the small black wire has been in the circuit for every test (doesn't look like any wrench marks on the nut)>

Tom

Do you mean the black wire on the 140A ? I remove all 4 of those wires so there are only studs.

 

1) Remove and pin back the +ve cable from the drivers battery. Remove the cables from the passenger also.

2) Remove all four wires from the 140A circuit so only two studs are left.

3) On A~ mode on mulitmeter ...... bridge from +ve terminal to the stud on 140A. Reads 0.5A.

4) Start pulling fuses in PDC and CAB as well as relays. No change.

You need to have power to measure draw. So the red lead must stay from the battery.

 

Now you could pull each lead and measure from the RED cable stud to the lead to measure draw of each wire.

 

With power still hooked up you can pull one fuse at a time and measure across the fuse terminals of the panel and see the draw level of each circuit. When you find the heavy draw circuit tell me the fuse and I'll pull up the wiring diagram for it.

 

Right now you need to work your way down the power distribution system and find out which circuit is the heavy draw. 

Commonly on many vehicles, it's the underhood light. Unplug it & see if the draw dissapears. Other than that, I agree with our fearless leader. Pull a fuse at a time to isolate.

 

Ed

I tend to forget about the under hood light being both my truck have burnt out bulbs...

Tom

Do you mean the black wire on the 140A ? I remove all 4 of those wires so there are only studs.

 

1) Remove and pin back the +ve cable from the drivers battery. Remove the cables from the passenger also.

2) Remove all four wires from the 140A circuit so only two studs are left.

3) On A~ mode on mulitmeter ...... bridge from +ve terminal to the stud on 140A. Reads 0.5A.

4) Start pulling fuses in PDC and CAB as well as relays. No change.

That is what has me confuzzled.You are saying the 140A fuse WITH NO WIRES ON IT still has the 1/2 amp draw.

Ill try and grab another video ...... but yes ........ all wires removed from the 140A ........ and still has a 0.5A draw when bridging from battery terminal with multimeter

You still measuring total draw. Now move into the other circuits and measure. Pull a fuse and probe both fuse contacts in the same socket.

Dumb question but have you isolated the batteries as in completely unhook everything from both and see if you don't have a bad cell draining the battery itself or just pull them and have them tested. I have not read through this entire thread very good but seems to be a lot of jumping around without starting at the source.

Good idea ..... apart from having the battery tested how else do I test the battery for cell leakage at home ?

If it was a battery drawing the other dow, you would get the .5 amps between the batteries. Just keep pulling fuses till you find the offending circut.

 

Ed