Bad alternator, Am I diagnosing this right?

[nosliw]

I've owned my deuce for about a month and haven't had a problem one starting it.

I had an electrical issue yesterday and a hot wire underneath the dash shorted out against the dash panel. When it did that, the whole electrical system shut down. No lights, no fuel pump, no warning buzzer, no gauges, naha. I fixed the wire that was poorly insulated and continued on my search.

There are three wires coming off my pretolite alternator. The small gauge wire that feeds the entire electrical system wasn't "hot". I spliced it into the positive (larger) wire coming off the alternator, and eureka, I've got power again.....

However....

I went out to start the deuce this morning and the batteries had lost enough charge to where it wouldn't crank the engine full revolutions to start.

So, I proceded to remove the batteries and take them to the shop to put on the charger. I noticed when I unhooked one of the positive terminals, a small spark occured, signifying that there was SOMETHING still on. There shouldn't be anything in the truck causing a spark of that magnitude, unless something was blatantly left on.

I checked all the lights, main IGN switch was off. Nothing at all turned "on" in the truck.

I suspect alternator diodes burnt out from my "short circuit" experience?

I removed the alternator entirely to take to the service shop for inspection, placed the batteries on the charger and proceded to my Easter wild rompus.
Before I left, I wired the "main electrical system" wire (small wire at alternator) into the larger power wire at the alternator so i could get the thing started and moved once I got the batteries charged.

When I went to hook up the batteries again after the charging process......No spark occured whatsoever at the teminals.

I suspected the positive diodes to be burnt causing an electrical drain on the positive side, since that was what i shorted out.

Since the only thing I removed from the eletrical circuit was the alternator, and now I don't recieve a spark when I hook up the batteries,

Am I on the right track?

I want to put it back to the way it was. It was charging fine and never failed to show the least resistance in cranking even for sitting 5 days.

The alternator is off and in the back of my pickup. I'm wiring in a 30 amp fuse at the "main" power wire coming off the alternator just to prevent any more issues with short circuits.

 

[bottleworks]

If I follow you correctly, it sounds like you tied your sense wire for the alternator to constant power. That's why you have a power draw. The alternator is trying to charge. The regulator is powering the field the entire time the truck is off (with the way you wired it). I suggest getting the wiring diagram and correct the truck to the way it should be. You may have damaged your alternator now.

I have attached a diagram.

The accessory switch looks to have it's power supplied from wire #10.

 

[nosliw]

AHHHHHH.....from the looks of the diagram, and the way i interpreted it, i thought the #1 wire is what feeds power to the ignition switch. that's exactly what you said, the sense wire. I backfed power into the sense wire to get power to everything.

no wonder the battery went dead.

i'm curious as to whether my alternator is still good after leaving the field on all night. i guess it would theoretically be the same as leaving the ign switch on all night as well.

so, i need to be looking for a burnt wire in the #10 circuit.

The wire that shorted out, i believe its a wire going to a circuit breaker. the are two devices directly beside the resistor for the heater that bolt to the inside of the dash panel. I'll get a number on what shorted before I leave for work, but I'm thinking that's what they are.

I bet I've got a wire burnt it two right at the starter relay.

 

[avengeusa]

the small wire goes directly to the ign switch, you are correct, it turns the alt on

there is a grnd wire, it is obvious which one it is, it goes from the alt body to the frame

the charge wire is tagged with #2, it goes from the alt to the starter solenoid on the starter

and there are 2 wires going from the soleniod, one goes to the alternator solenoid start post.....

which one is burnt?

 

[nosliw]

i looked in the engine compartment this morning and looks like #10 goign to the starter relay is crispy. although, it's been taped up like there's been a problem before, so who knows.

the original short occured at a wire with three metal tags, 87 106 and 39 respectively.

I'm going to check my alternator on the bench this morning for current draw. i've misdiagnosed where the power interruption has occured and caused the battery to drain by keeping the field ignitied all night.

i'm hoping my alternator is good.

i'm installing a fuse in the #10 wire to eliminate this problem in the future!

 

[cranetruck]

For further reference see the PS mag section of the old site.
Steel Soldiers :: Military Vehicles Supersite

Also, the #10 wire is "fused" with the circuit breaker as shown in the original wiring diagrams.

 

[avengeusa]

I replaced my wire from the relay to the solenoid, it was bad, got a heavy gauge batt wire from autozone and did a slight mod to make it work, but like the diagram above, if it is charging, it is good.......

the little wire has to be switched

 

[nosliw]

i just checked the current draw on the bench, without the field ignited, zero current draw.

with the field ignited, 2.38 amps.

i'm thinking the diodes should be good. I'd think if the diodes were bad, it would show a draw when the field isn't ignited.

either way, i'm chasing my tail. the alternator should be fine as long as it's charging, and not showing a current draw, correct?

in the diagram posted above by cranetruck, i see a voltage regulator.

in the other diagram posted by bottleworks, i don't see one.

????

this one is a prestolite brand. does that make a difference on the presence of a regulator?

 

[avengeusa]

your alternator should be an internally regulated unit? correct, 60 amp?

got a pic?

 

[nosliw]

here's the best i could get with my camera phone.

 

[nosliw]

i installed the alternator, and my two new belts that it desperately needed; re-arranged my wires back to original form, tried the main switch, to no avail, so I started probing.

good voltage at all places i could check on the #10 wire coming from the starter relay to the closest point i could get at the harness before it got taped together. i removed the ignition switch, and started probing, found two hot wires, and two that weren't. grabbed my wiring diagram and re-familiarized myself. grabbed the handle and flipped the switch just to see if the power was being switched.....and....

somehow....everything lit back up.

i don't know if it was a bad connection at the terminals od the switch, and when the wires shorted out, this happened to be the path of least resistance or what...

are these switches protected somehow by a circuit breaker internally that resets when you remove a ground source???

i don't know. i'm lost. it's a mystery to me.


but anyway. it's fixed for the time being.


thanks for the help guys. i'm sure it will rear it's ugly head again in the future. probably at the worst time.

i'm sticking that wiring diagram in the glovebox and keeping it there for quick reference!!

 

[3d63]

hello I need some help with the charging system on my 71 duce . the voltage reading I'm getting at batteries while running is 23.4 can I adjust alternator output and ifso can someone give me direction thanks for any help on this matter