Fall 2019 I did the 3g conversion for the alternator on my 74 f250 (fe360). I haven't have a chance to do much more work on my truck since then as I don't have a garage and its been sub freezing temps. My issue is from day 1 the voltage output has been as high as 17-18volts. I of course didn't drive like this. It was brand new alternator from autozone. Should I return it or is there a connection I may have missed along the way thats causing this?

 

Is that at the guage, or with a multi meter.? Problem I'm having is, it reads 14.3 output at the (3G) alternator and the batteries, but 12 - 11 volts at the guage. I checked the feed to the guage: 14.3V. Cheap Bosch auto zone guages give bad readings. Multi meter doesn't lie.

 

It’s the read out on my efi display which I’ve tested against my meters to be accurate, and you can hear the electric fuel pump surging when the when the voltage spikes. The only dash gauge I have is the discharge/charge ameter that was stock. And when the voltage spikes it pegs that to the charge side.

 

It might be a bad internal regulator. If you can, pull it and take it back to AZ and have them bench test to confirm.

Take your meter too.

 

This normally happens when the yellow wire is connected to the wrong location. Where is the yellow wire going to? Hopefully it's not connected directly to the output lug.

 

I just wanted to toss in what I learned about 'rebuilt' parts from AZ and O'reilley's, and most of the rebuilders. I used to believe that rebuilt meant all new parts. But that is not the case. If an alt is being rebuilt, and they test the oem v.regulator, and it is good, whether it is 1 or 40 years old, they will not replace it. If a rebuilt fails, they replace it free. That is why the rebuilts I used to buy, whether master cylinder of alternator, would last on average, about 18 months.

 

Where should it be connected?

 

In factory 3g installations it is connected to the underhood fuse box. For you install it's best to get it to the battery or to the hot side of the starter solenoid. This provides the most stable voltage control. Others also take the time to run it to the interior fuse box.

 

When we did ours, the written instructions I got from another thread said to run the yellow wire to the battery lug of the alternator. The diagram however shows it running to the hot side of the solenoid. We ran it to the lug on alternator. Voltage at the battery after initial install was between 14-15 irrc. I'll check it again tomorrow to double check it is not overcharging.

I'll attach the instructions I used if anyone wants me to. I think I got them from the "Tips and Tricks" sticky.

 

Yes, there are literally thousands of 3G's working properly with it connected there. But I'm still with gashog that it should be run to the battery, like Ford and everybody else always has done it (other than with 1-wire alternators of course). I'm not sure the interior fuse box is the best for an old truck either, so I say run it to the battery side of the starter relay/solenoid.
Easier and a shorter run anyway I would think.

I'd naturally assume a bad alternator/regulator at this point, and as suggested, have it tested.
But to confirm, you have the Green w/red wire getting 12v only with the key ON, full battery voltage at the Yellow w/white wire all the time, and the White w/black stator wire is attached to the connector on the side of the alternator body?
Verify that the Yellow wire and your charge cable both show the same voltage as found at the battery itself.
What size charge cable did you install?

Just a few more questions for filling in all the blanks, but having it tested will ultimately be a good thing. Before any kind of warranty is up!

Paul

 

Checked voltages this morning.

Key off 12.6
Fast idle at start up 14.6
Lights, blower on high RPM @2000 14.6

Here's a picture of our connections.




We've organize the wiring since this picture.

 

Agree. I read your post too quickly and thought you were questioning connection to the battery lug.

 

When I did my 3g upgrade, I read that the simplest way to hook up the yellow wire was to connect it the post on the alternator. I did it that way and haven’t had any problems. But I found this article on “how to build hot rods” that says:

Do you guys think this is right? The yellow wire “reads” how much voltage is needed and the alternator responds to that reading? Sounds like magic to me.

 

It's no magic, it's why I hate seeing it jumping to the back of the alternator. If Ford could have done that on millions of vehicles they would have. It's a voltage sensing reference wire. You want to run it downstream to where the cabin pulls power from to give steady power at proper voltage. My experience is with a 2ga cable and the yellow wire at the starter solenoid you will have a .8- 1.0 voltage difference from alternator to hot side of solenoid. This is very evident when cabin power is being pulled through. With the yellow wire at the alternator it can't compensate for voltage drop and you don't get proper performance.

 

With all this discussion, I think I'll move mine to the solenoid tomorrow. I'll post up the new voltage readings also. I interested in whether or not they'll change.