I have a 1980 Heritage. Its a camper with a 1980 truck base. I think the manufacturer just modified the electrical system to add the camper and a second battery. This involves sending power to the second battery, and involves a limiter to prevent the primary battery from running down if your camping and using the second battery for lights, otherwise the truck wont start!
Here is the problem. The electrical system looks factory, same alternator and the IC regulator. For whatever reason, my truck charges at only 13 volts until you unplug the regulator, then it heads for twenty and off the scale. The alternator was changed to no effect because this part was 40 dollars and the ic regulator is..you dont want to know. My helpful electrician neighbor opened the ic regulator (not the sealed part, just the back) and found a diode blown. he replaced this. I also found that the primary battery has a white wire coming back to positive that was fried out. I reconnected the repaired regulator, fixed the bad wire and started the truck. After the blinding flash from under the dash, everythings back to the original inop cond. except now I have no interior/exterior lights. Should I risk a new IC regulator on this?

 

If I were you, I would risk it. If it works, then you have figured out the problem, but if not, at least you have a new IC Regulator.

 

You're talking about the external regulator, right?
You can get remanned ones from a parts store or used off of ebay or BBSs like this one relatively cheap. It's not a dealer only part.

The positive on what ? The output of the alt to the batt is a white wire, it also goes to the ext regulator.