Possible Electrical Short?

Which fuse is blowing? Were's it located?

 

The fuse that's blowing is the 10 A Gauge fuse. It's in the fuse panel in the cab on the drivers side.

 

page 4 and 5 tell you what the gauge fuse powers. (see pdf)

 

Wow, talk about a giant fuster cluck. I found one ground that looks like it's shorting out with motor vibration. I gerry rigged a ground wire with some extra 12 g I had lying around and then started checking volts again. Battery was dropping down to 11 V and the alternator was only cranking out 12.2 so it looks like this did kill my battery and my alternator (never going to that shop again since they "tested" both and said they were good), although they may be unrelated, or this may be a chicken or egg paradox as well. Either way, after much testing, it does look like I may be on the right path. I'll replace the ground wire with an actual ground wire, put in a new battery and new alternator. It's over 100 degrees outside so I'm coming in for the night and will cool off with a few beers but I'll update everyone tomorrow once I replace all the parts again and hopefully this problem is all fixed.

 

I don't think it killed the battery if you were able to start it. Swap in an alternator 1st before spending money on the battery.

 

Its possible the alternator has an internment short in the main charge wire circuit.

 

I was just curious I have seen people fry the Meter trying to measure Resistance on live circuits .

Maybe the disconnecting of the negative cable was not mentioned .

How many miles are on the vehicle in question.

At least your getting closer

 

That would be a good thing to do. I'm used to using a fluke and its not critical with it. It just switches to a voltage reading.

 

Good Meters tend to have protection .

The cheaper ones just get tossed then the hassle of getting another one,

 

May be a slight detour, but bear with me. If the 120 a alt fuse was bad or had a bad connection, would it decrease the alt output? I took my alt back in to the shop and its reading at 14.3 v on their machine.

Yesterday I was watching battery voltage drop while trouble shooting and since it's a 6 yr old battery, I just replaced it to be safe any way..so now the bat is brand new, alt is tested good and I'm still only getting 12.2 v from the alt while running.

 

And to answer jons point about the main wire. Its in pristine shape but I did test it and flexed the wire while checking and didn't see any changes in the readings.

 

Unplug the smaller wires and see if there is a change. Also unhook main charge wire and tape the end up. Run truck and see how it acts and voltage also.

 

Just where are you measuring the Alternator output while running??

The B terminal of the Alternator should be the first place if you have the correct output there

Then the fuse block at the 120amp protection

Then the positive battery post

 

Yes the alt fuse being bad or bad connection would lower output.

 

Also with voltmeter check for voltage from the center of the neg battery POST to block or intake manifold. (Engine running)
Do the same for ohm reading.

 

I'm measuring output from the terminal on the alternator to the neg battery post, and double checking from neg bat to main fuse connector, and pos bat to neg bat.

If I did everything correct, here are my numbers...

Normal running voltage is 12.4
No change when I disconnect the plug from the back of the alternator.

With main fuse removed, from alt to neg bat is 1.1 v
Pos to neg bat is 12.4.

Neg bat post to block is 0 v and 9-12 ohms...it wouldn't sit still, kept fluctuating.

Not sure what any of this means or if I even did the tests right but hopefully the numbers make sense to you.

 

Check the negative battery cable really good
All the way to the block for loose connections. Also post a picture of your battery terminals.

 

picture should be attached if I did that right

 

Good picture. Clamps look good.

 

And here are the two ends of the neg. The rest is in the heat shield but I can cut it out if I need to. I tested resistance on either end and didnt see a need to go any further, but will gladly if it may help.