Ford Repair: 1990 Aerostar battery gauge, regulator failure, battery gauge

Question
I'm experincing a high reading while driving.  All is normal early on, but after 15-20 minutes, the dash gauge spikes and stays high while the engine is under load.  It seems if it stays below a certain rev, it OK, but under acceleration it goes high.  The van has a manual transmission.

Answer
First check the voltage at the battery, with the key off and with the engine running. You should see a voltage with the engine running 1-2.5 volts higher than battery voltage. If the charging voltage is more than 14.5V then you may have an alternator/regulator failure.

The factory ampere or voltage gauges were never very accurate, I suggest you go by what a voltmeter tells you at the battery