I replaced the voltage reg with one that worked fine on another truck. I'm getting < 12 volts at idle and then it moves up to 18 at about 2000 rpm. The battery was fully charged and cranked fine. It reads about 12.8 when not running.

The question is if I replace the regulator do I need a special one for the 100 amp alt or will the standard one work.

Second question, is there a way to adjust the output so that it's higher at idle without changing pullies?

 

How much do you love your alt? The reason why I ask is that I would replace it with a GM one-wire unit. You can find these used for $25 on most GM big sized cars. They put out anywhere from 85 to 145 amps depending on what you pull it off of (look for one with AC and power windows to get the best amp rating). It will bolt right up to where your old amp was and give you tons of power.


To answer your question, 12 volts at idle might show a problem with the low side feed on the reg, or it could be that your truck is ideling just a tad on the low side. Autozone told me that they listed only one reg for all alts used on the 77-79 systems.

 

the problem is that it's a new high output alt and crome plated so that it matches with the rest of the stuff. I'd really hate to replace it.

I called around and found that most carried the stock one, but I could special order one for higher amp ratings for about $50 vs $11 for the stock unit and I really don't understand the difference. I thought the regulator just regulated the output of the alt to keep it within a certain range.

I also thought that Ford has some older units that had an adjustment on them. I thought I read about that in a manual once where it had an adjustment inside the regulator that you could set it manually.

 

I'm not really certain on this but I suspect Ford used the same regulator on everything. You might check to see if the same part number applies to a big old Linlcon with everthing on it. What are you using for a volt meter? You should see about 13.2 to 14.5 with the engine running. 18v will burn up your battery.

 

I looked up some of the newer alts and found the the 82-up trucks had an option 100amp alt. I looked at one in the parts store and it looks EXACTLY the same and it was < $12.

I installed it and it works like a pro! Now everything works including the new stock location volt meter

Thanks for the help.