Alternator, or Voltage Regulator?

[FordGuy100]

So I'm driving the black beast (1989 f350 CC SRW 2wd ZF-5) because a) less miles on my truck, b) it has functioning AC, and C) because if the ZF it gets 18mpg easy, which I can't get in my truck.

Anyways the voltage gauge (stock I know I know) has always been a kittle goofy. If I turn the fan speed from nothing to full it drops way down at idle, and comes up if I rev it. I didn't think much about it since all the other gauges are a little goofy as well.

But tonight I caught onto something. Sitting at idle with the lights on and ac going full boar, the lights are kinda dim. The voltage gauge is reading towards the 9v area. If I reced it, the lights would get brighter and the gauge would swing back to the 12v area. If I turned the ac off it would also get a little brighter as well.

What do you guys think?

 

[Compu Doc]

Check your belt tension first. If that's good then replace the regulator if it is external because it is cheaper than an alternator and being it is putting out something going from 9-12V the alternator might still be good. Your truck should be putting out between 13.5V-14V and mine does that easily at idle.

 

[Hyde]

Try the reg first... ask me how I know.... but a brand new alt is always nice Not sure about the 87+ trucks but on my 83 the regulator was the same one it had been for the previous 15+ years on Fords.

 

[MIDNIGHT RIDER]

A sure indicator of a completely failed alternator in a Ford truck is all the gauges will go haywire.

The temperature, oil-pressure, fuel-level, etc., will usually all go all the way to the right.


A regulator is usually either good or bad, with no middle ground, so I tend to think that most likely the alternator is on it's last legs.

Of course, you have already fixed all the kindergarten stuff, such as cable connections, GROUNDs, belts, etc. that could also cause these symptoms.

 

[Hyde]

The temperature, oil-pressure, fuel-level, etc., will usually all go all the way to the right.

Ive had that happen... Knew something had to be wrong when the fuel gauge was at full so I pulled over and they all went back to normal...

 

[Black dawg]

first verify voltage with a meter. then with everything on, jumper the a and f terminals at the regulator, if voltage goes up regulator is not working correctly. I once tried 5 different regulators from napa that would let the voltage under load get pretty low, the factory original out of my 79 bronco worked perfectly , and still is 5 years later. If the voltage does not come up the alt is probably weak.

 

[bigoilburner19]

first verify voltage with a meter. then with everything on, jumper the a and f terminals at the regulator, if voltage goes up regulator is not working correctly.

X2

 

[FordGuy100]

Voltage definatly comes up, but I need to verify with voltage reading.

 

[93f250idi]

got a brand new autogage volt meter ill sell for $10 plus shipping. bought with a gauge pod and replaced with a pyro in the pod. pm if you want it. i can get pics tommarow if interested

 

[CDX825]

Maybe time for a 3G swap

 

[FordGuy100]

No I have a multimeter I will just take some readings under the hood.

 

[typ4]

that alt behavior is pretty normal with a 1g at idle. the 3g will charge more at idle.
Also a rebuilt unit may have not the same clearances from the rotor to stator and cause low idle voltage.

 

[FordGuy100]

I think it has been rebuilt. 89 trucks have 1G's?

 

[CDX825]

1G has an external regulator, the 2G is like the 3G and has a built in regulator.

I thought that truck would have had a 2G

 

[typ4]

my 91 has a large case 1g