94 Mazda B4000 electrical problem

[AzRockRunner]

I have a 94 Mazda B4000 ext cab 2x4 and it runs fine but is killing the battery. I drove it to checker, they tested it and the alt failed. So I removed the alt, took it in and tested it out of the truck and it passed with flying colors. So I put it back on the truck, jusp started the truck and the new battery is down to 10.5 volts even while running. I tested the output wire on the back of the alt and it is not puting out ANYTHING!!!!!

So, my question is where do I look now. Alt tests good on bench but will not charge the system in the truck. Do I have a bad PCM? is there a sensor somewhere? What am I missing

Thanks in advance

[skippy]

I have a 94 Mazda B4000 ext cab 2x4 and it runs fine but is killing the battery. I drove it to checker, they tested it and the alt failed. So I removed the alt, took it in and tested it out of the truck and it passed with flying colors. So I put it back on the truck, jusp started the truck and the new battery is down to 10.5 volts even while running. I tested the output wire on the back of the alt and it is not puting out ANYTHING!!!!!

So, my question is where do I look now. Alt tests good on bench but will not charge the system in the truck. Do I have a bad PCM? is there a sensor somewhere? What am I missing

Thanks in advance

voltage regulator?

[martin]

I can't find the diagram but, the alternator is internally regulated and I believe it uses one of the small wires that connect to it as the reference voltage for the regulater. that being the case you should have 12v (or close to battery voltage) on one of the small wires when the ignition is in the run jposition.

[svtdawg]

What great timing for this post. I got on here looking for a similiar problem I'm having with my 95 ranger and here it is! Maybe we can work together on this. Here is what happened to me couple weeks ago. Battery was getting weak...then truck wouldn't start. Got a new battery and the truck ran great...until it died on me, while I was driving! OK, so alternator right? Well, I didn't do any analysis the first time and just threw money away for a new battery that I didn't really need so I figure I better start. Pulled the alternator and had it tested at a good local shop, not a chain autoparts store! Guy rebuilds alternators for big rigs and everythings else. Said it was perfect. Puttin out right amount of voltage and amps with and without a load.

Sounds like your problem too, right? If you got your alternator checked out then it's not the voltage reg.

Here is what I'm trying next. Put alt back on and trace wires from alt to motor. It's the only thing in the equation that makes sense to me. If the alternator is good and the battery isn't getting charged then I'm thinking wiring or whatever is between.

Anyone out there with any help?

There is a 3 wire pigtail, small grey wire and the bolt-on fat red positive wire on back of the alt. I'm suspecting the 3 wire pigtail right now. Those tend to go bad on Fords from my experience.