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.

 

Failed at both places I tried.

New one here friday morning.

 

Will update.

thx

Well draw went from 0.5A to less than 0.2ma engine off after alternator pulled.

going to get it bench tested

That was what your posts were pointing to. I am glad you got it figured out! Just make sure that the new alternator puts out less than .1 volt AC.

That was what your posts were pointing to. I am glad you got it figured out! Just make sure that the new alternator puts out less than .1 volt AC.

Think mike had an example of testing this right ? Correct way to measure ? 

Red probe at the BATT terminal on the back of the alternator and black probe on the NEG battery post. Start the engine and measure.

Red probe at the BATT terminal on the back of the alternator and black probe on the NEG battery post. Start the engine and measure.

Just remember to set the meter to AC volts.

So just got the alternator installed after they couldn't source a unit till after thanksgiving and then the one arrived tested bad.

Installed it ...... still a 0.5A draw.   I tried to grab a video but pretty dark ......... I'll upload as I can ...... ideas ?

http://vid1059.photobucket.com/albums/t430/fakdaddy/truck/20141128_180004.mp4

So just got the alternator installed after they couldn't source a unit till after thanksgiving and then the one arrived tested bad.

Installed it ...... still a 0.5A draw.   I tried to grab a video but pretty dark ......... I'll upload as I can ...... ideas ?

So, you are saying the alternator they got in tested bad and you installed it? Am I reading your post right? You don't have any other wire going to the 140A fuse, correct?

No I had to wait for a good alternator as the new one they initially got for me tested bad.

So this one tested good ........

Always have the alternator bench tested before you leave the store. I've heard this so many time to come home install their new alternator and find they got another bad alternator.

Always have the alternator bench tested before you leave the store. I've heard this so many time to come home install their new alternator and find they got another bad alternator.

It was bench tested as good at store. I had to wait and extra 2 days as the 1st one they sent bench tested bad. This one I installed was tested good.

Better Video hopefully

 

http://vid1059.photobucket.com/albums/t430/fakdaddy/truck/20141129_095922.mp4

The black wire that you are saying is a ground off the fuse is the wire that goes to the big terminal on the alternator. Now here is what I would like you to do. On the one side of the alt. fuse there are two wires. Pull BOTH wires off the fuse and check the amp draw on ehch wire individually. The was it is set up you are checking the alternator and what ever the other wire is going to. You need to separate them to isolate which wire has the draw on it.

Not sure if I followed exactly ...... but removing ALL the wires on the ALT fuse (both sides) showed me that there was still 05.A draw between the battery and the ALT fuse terminal posts (no wires either side) when bridged with battery. So no wires connected on either side of the alt fuse terminals posts ........ bridging from battery to EITHER of the empty posts had 0.5A draw.

If you pull all the wires then test to the fuse the problem is in or on your 140A fuse. There is some way for the voltage to be leaking to ground. Either it is internal (not likely) or external.

Then pull each fuse one at a time and measure amp draw across each fuse socket you pull out.

If you pull all the wires then test to the fuse the problem is in or on your 140A fuse. There is some way for the voltage to be leaking to ground. Either it is internal (not likely) or external.

 

Not sure what you mean. That theres a problem with the 140A fuse itself ??  How would that place a draw on a circuit if the components have been removed.

 

Then pull each fuse one at a time and measure amp draw across each fuse socket you pull out.

 

But we are talking about the 140A fuse circuit for the alternator. If all the wires are removed from both posts ...... can anything else be linked ???? Unclear here also. 

From the alternator fuse everything else is powered in the PDC so I would pull one fuse and probe each fuse socket with the amperage meter. When you find the socket drawing the heavy load then you at least know what circuit. Then after the PDC then move to the in-cab fuse panel.

 

 

 

 

From the alternator fuse everything else is powered in the PDC so I would pull one fuse and probe each fuse socket with the amperage meter. When you find the socket drawing the heavy load then you at least know what circuit. Then after the PDC then move to the in-cab fuse panel.

 

PDC.png

 

pdc1.png

ha !! Your guys are killing me .... need a dumbed down explanation.

Are you saying that the alternator fuse not only protects the alternator circuit .... but the entire PDC as well ?

 

I want to understand why with everything disconnected from ALT circuit there is something still able to draw on that circuit ........ so Im guessing that has to be the case and also the reason your saying to pull other fuses ?

No. The Alternator fuse is hooked at the head of the main bus going into the PDC so it has the illusion of the alternator and PDC both.

 

The black lead on the alternator should be dead without a fuse in place.

 

The red lead terminal is the battery supply and also powers the PDC main bus. So now the loads as shown above break off in separate fuses. Then break off again to the Cab fuse panel too.