Voltage drop when the fan is on

[cycleguy55]

Originally Posted by SBSerpent

Without the fan on, the voltmeter is indicating around 14V. Fan kicks on and it drops to 12V or even lower when at idle or at a stop light. Amazing how much a drain the fan is on the charging system.

Running a 1G alternator? If you're not hung up on period correct look of 1G, switch it out for a Ford 3G alternator. Internal regulator and fans, higher capacity and widely available. Easy bolt-in swap with some minor re-wiring to eliminate the external regulator. Serpentine pulley is easily removed and replaced with V-belt pulley. Mine is a 130 amp rated unit that fits a 1995 Mustang V6 and can generate more amps at idle than my 1G alternator could generate at 2,000 RPM.

The only caution I would offer is the higher output at idle of the 3G may cause belt squeal if things aren't 100%. Some go to double pulleys, but I'm running a CVF Racing billet aluminum pulley - the aluminum seems to do a better job of grabbing the belt. I also run a turnbuckle type adjuster from CVF that allows for finer tuning of the belt tension than does the old slider and bolt style adjuster.

Alternator output curves:



Left to right: 1G, 2G and 3G alternators - avoid the 2G:



3G alternator - note V-belt pulley:



Wiring diagram - minor changes:



Check this out article out for all the details (and more photos): https://www.hotrod.com/articles/inst...r-older-fords/