Quick Question. . .

[ftpiercecracker1]

Will our trucks continue to run if battery positive is disconnected? Under the circumstance that the alternator and all associated wiring is intact and functioning as intended.

 

 

This question is pertaining specifically to a 90, 4.0l, ax-15 equipped MJ with no modifications.

[Pete M]

not only can it, the truck should continue to run off the alternator. :thumbsup:

[ftpiercecracker1]

Well then we got problems sister.  :help:   

 

During a routine U turn i had to drop off the curb, it was a good jar, but nothing i had not encountered before only this time the truck died along with all electronics as soon as i got back into my lane. Like i turned the key off, instant. Thankfully, i was in a nearly deserted area so traffic was a non issue. I popped the hood to discover that the wire that runs from battery positive to the starter relay had been yanked out, which to my understanding is basically where/how power is distributed throughout the rest of the vehicle. So i stuck it back in as best i could and the truck fired right back up and all electronics came back, no worries i thought. I will just pull that wire back out, tuck it out of the way, and make the neccessary repairs at home. So i went back under the hood and pulled the same wire back out, truck ran great for about three more seconds and then boom, dead, instantly. Again like someone turned the key off. I went through the same procedure once more with the same results. I KNOW my alternator is working, i have checked at the battery with a multimeter to confirm and my voltmeter in the cab is ready a rock steady 13.98v, approx.

 

 

Sooo what gives?   :dunno:

[Eagle]

Back in my pony car days, when I graduated from autocross to road tracks and hillclimbs I decided it would be a good idea to have a kill switch next to the shifter handle. I wasn't sponsored and I didn't have a lot of money, so I went to Radio Shack and bought a small-ish "project box" and a push-pull switch. Out was ON, and in was OFF. I mounted the box to the tranny tunnel and drilled a hole in the top for the switch. That part was great -- up was on, so to kill all power all I had to do was drop my hand from the shift knob to the switch, and it was OFF.

 

Except ... that it didn't work. I don't recall how I wired it the first try, but what happened was that, when I hit the kill switch, instead of killing the engine it kept right on running ... and the lights got brighter. Whatever I had done, what I had accomplished was apparently to just remove the battery from the system so the alternator was running everything directly.

 

It took me awhile to figure out how to get around that, but I did find a way. Wish I could remember, because it might help you here.

[Pete M]

do you mean the small + wire got yanked out?  or that the big + cable fell off the terminal? 

[ftpiercecracker1]

On the   (+)   battery terminal there is the large 2 gauge wire that is directly ran to the starter. The other is a smaller possible 10-12 gauge wire ran directly to the starter relay stud. Its very short, maybe 7 inches long. When the battery slid over it yanked the small wire out of the ring connector that attachs it to the starter relay stud.

 

 

 

 

EDIT: i checked the alternator wiring and all seems intact and fine. Aside from the plug in the back of the ALT there is a medium heavy gauge red wire that runs from the back of the ALT directly to the starter relay stud. I would assume this is how the ALT supplys power to the battery and the rest of vehicle.

[jimoshel]

. Pull the plug from the back of the alt. Pin 1, Brn wire should be reading 2.5-3.0 Volts with the ign on.

[ftpiercecracker1]

And if not?

[jimoshel]

That's your exciter voltage. It's applied to the field windings. Needed for the alt to work.

[ftpiercecracker1]

Okay, finally pulled the plug on the ALT, the two wires going into it are a solid yellow wire and a tan w/ a black stripe.  Tan with a black stripe read about .13 volts and the yellow was 12.48, pretty much full battery voltage.