Upgrading Alternator

You are all overthinking this

FIRST all these cars logged millions and millions of miles "back then" with nothing more than about a 35 amp alternator and they worked "OK" and by that I mean, yeah, the lamps might have dimmed at an idle, but hey, HOW LONG DO YOU DRIVE THE CAR when it's idling?

The wipers certainly didn't stop working just because the alternator was not keeping up!!!

HERE is your possibilities:

SOMETHING is wrong with your present alternator, that is, you have one or two bad diodes, some bad windings, and is not CAPABLE of putting out ORIGINAL rated output

Second, the age old "bulkhead connector" or other related trouble.

The way you describe this problem, I would not be suprised if the IGNITION SWITCH is not the problem

Putting a BIGGER alternator on the car IF and (probably) when you have a wiring/ switch/ fuse panel problem, will only make it worse. Can you spell "let the smoke out?"

SO do this first:

ONE make sure the battery is charged and find someone to LOAD test the battery. This is for just general "good," not necessarily part of this problem

Inspect and CLEAN the battery terminals. Make sure the main ground is to the engine block, and make sure there is at LEAST a no 10 ground from the block or battery to the body. If any doubt, add another

Take apart your bulkhead connector, inspect, and clean. I'd bet money this is an issue

Then get down at the fuse box, and measure the voltage on the SWITCH side of the fuse key on, engine off, wipers/ radio/ lights/ etc off. Then turn on the wipers and measure the voltage on BOTH SIDES of that fuse

Then go up to the battery positive and clip your meter to the battery post, and make the same measurements, IE wipers on, wipers off at the battery

Post those readings

Read this article about bulkhead connectors:

http://www.madelectrical.com/electricaltech/amp-gauges.shtml

more good articles:

http://www.madelectrical.com/electrical-tech.shtml