Dual fans What size alternator?

What is the amp rating of the fan motors? If they are protected with a 30 amp fuse, I would think the factory alternator would support them just fine.

BUT your post hints at a far bigger problem! Where exactly are these fans getting their power?!? If the amp gauge goes up when they come on, it would suggest that their operating load is traveling through the amp gauge which means it is also traveling through the ignition switch and most importantly the BULKHEAD CONNECTOR. You should fix this as soon as possible, as it WILL cause problems (think ELECTRICAL FIRE)! Connect the main power lead for the fan relay directly to the output post on the alternator (best), the supply side of the starter relay (good), or the positive battery post (OK). Any of the three will make the fans work better and the 40 year old harness last much, much longer.