Low voltage - 12.5v with new alternator

[Bronco Sport]

I changed the battery, alternator, voltage regulator, starter solenoid, and still only get 12.5 volts at idle. Any idea what to check…. I suspect it might be a ground issue some where. Has anyone else had this problem? It’s a stock 289 with a stock alternator. I also have a current draw when it's off that I've not been able to isolate. I have a new ignition switch that I'm going to chance out the old one with.

Thanks for any help.

 

[Viperwolf1]

What's the voltage of the battery with engine off? Does the voltage increase when the engine is reved?

 

[73stallion]

did you replace the voltage regulator?

 

[Bronco Sport]

What's the voltage of the battery with engine off? Does the voltage increase when the engine is reved?

It's about 12.3 with the engine off. The voltage goes up to 12.8 or so when the engines is reved to 2000. I did replace the voltage regulator too.

 

[Viperwolf1]

12.8 is still too low. Make sure the regulator case is grounded directly to the alternator, the green-red wire has battery voltage with ignition ON and the yellow wire has battery voltage. Look at the alternator and regulator wires and connectors for damage or corrosion.

 

[Bronco Sport]

12.8 is still too low. Make sure the regulator case is grounded directly to the alternator, the green-red wire has battery voltage with ignition ON and the yellow wire has battery voltage. Look at the alternator and regulator wires and connectors for damage or corrosion.

I'll take a look. Thanks for the advice.

 

[RRRAAAYYY2]

The regulator is grounded to the firewall. It has to be installed before the wires are plugged in. Did you plug the wires in first? If so you likely damaged the regulator. Ask me why I am telling you this? Becvause everyone does it, so dont feel bad if you did.

 

[DirtDonk]

Also check to make sure that your radio noise supressor (if you still have one) is not going bad and partially shorting to ground.
In case you're not sure, this is the little cylindrical thingy that's fastened to one of the regulators mounting bolts and has a yellow wire that joins to the other yellow wire at the regulator.
More often than not, there's a bad wire or connection behind your type of issue, but if your noise supressor is grounding out, your regulator may be sending an incorrect signal to the alternator.
Not really sure if it would tell it to under-charge or over-charge, but they're always worth a check anyway. Maybe RRRAAAYYY2 or Viperwolf will know if that's legit, but in my experience, those things will really throw you for a loop trying to track down a phantom gremlin.

Paul

 

[quikdrummer]

or just do what i did and snag a one-wire internally regulated GM alternator, take a drill to the upper mounting hole, get an extra spacer, and get an instant 14.5-15 volts with no hassle

heres a good page that gave the directions that i used, cuz i was having the same problem. http://www.rowand.net/Shop/Tech/GMAlternatorInAFord.htm

i put a brand new wiring harness in and replaced EVERY wire and every part, new alt, new regulator, etc... and my problem sounds the same as yours, barely getting any charge at all regardless of RPM. plugged this bad boy in, and not a problem since.

of course, then you risk the engine rejecting the transplanted part of the enemy...

;D

 

[Bronco Sport]

Also check to make sure that your radio noise supressor (if you still have one) is not going bad and partially shorting to ground.
In case you're not sure, this is the little cylindrical thingy that's fastened to one of the regulators mounting bolts and has a yellow wire that joins to the other yellow wire at the regulator.
More often than not, there's a bad wire or connection behind your type of issue, but if your noise supressor is grounding out, your regulator may be sending an incorrect signal to the alternator.
Not really sure if it would tell it to under-charge or over-charge, but they're always worth a check anyway. Maybe RRRAAAYYY2 or Viperwolf will know if that's legit, but in my experience, those things will really throw you for a loop trying to track down a phantom gremlin.

Paul

My voltage regulator does have a very old little cylinder hanging off of it. I wasn't sure what it was. I'll remove it and check all of the wiring. I made sure the regulator had a good ground before I plugged it in. It doesn't appear to be the regulator since I get the same reading with the new and old one.

 

[oleguy74]

that round thing is a noise suppression capacitor.unless it is shorted won't affect anything.you can disc it to check.