1975 Ford F-250 highboy charging issue
 

1975 Ford F-250 custom highboy
390
4x4
My dad has this truck and has replaced the alternator and the voltage regulator. When we put the volt meter on the battery it reads 12.2v. After we ran it for a while with the lights on it dropped to 11.7v. Shouldnt this be showing around 13.5 volts which would tell us the charging system is working? If its not the alternator, battery, ground, or the regulator, which are all new, what trouble shooting can we do to determine the problem? Your help is appreciated in advance, thanks!

Just recalling from memory, which ain't what it usta be, Suggest you run a separate wire from the negative battery terminal to the voltage regulator mounting. It's a quickie , easy to do and will tell us if the regulator can be effective in controlling the output of the alt. Usually the regulator uses the sheet metal mounting for its ground and over time the ground gets lost because of rust etc. If that doesn't help, let us know .