I read the battery starts the engine and then the alternator charges the battery and furnishes electric power while the engine is running. The alternator on my 1993 F150 4.9L engine only has very small gauge wires (#14 or 12) attached to it. How can these small gauge wires furnish power to large current devices such as air conditioners, electric defrost heaters, etc.?

 

Those are the control wires. There is a large gauge wire that runs between a screw terminal on the back and the fender mounted solenoid.

 

It's the other plug that carries the alternator output.
2G alternators have a pair of 10Ga. wires spliced into a single fusible link that attaches to the hot side of the fender mounted solenoid.
You are looking at the regulator plug....

The rectangular plug with three terminals (two black/orange wires and a black/white stator wire) is known to overheat and fail, even with the engine off.

Many of us have changed to the later 3G style alternator because of this problem.
The 130A 3G can also put out more current at idle than the 2G at redline.

With the old 1st gen alternators that have a separate regulator there are individual terminals for each wire (but you can see that this is not the case here)

The small wires don't furnish power to high amp draws, the battery does.
If a 2G can only supply 60-65A max there shouldn't be an issue.
EXCEPT when that stupid plug corrodes internally and shorts out due to the heat.

The yellow 'sense' wire going to the regulator tells it to turn on but the truck doesn't get the current because of the failed plug.
The alternator keeps kicking out more until either the windings melt down or the harness catches fire (or both)

 

True, though, the alternator (Pictured) is a FIRE prone 2G alternator. It should have 3 larger wires connected that around #8 gauge, but still very crappy in a block connector.

I'd suggest doing the Mod for a 3G ASAP!!

 

Yep, that connector controls the internal regulator and volt gauge etc, there is a single post on the back of the alt the does the charging, depending on the amps of the alt determines the ga. of the wire, I've seen 10ga, all the way up to 00. For emergency vehicle's and such that have 240 amp alternators with seperate regulators.

 

Sorry, 10 gauge wire. Ardwtktrk posted just as I was typing and hit post.

 

Not in this case.

You can see the external fan.
This combined with the regulator plug can only be 2G.

3G (95 or 130A) alternators have the pictured plug and a single output stud on the rear, and a small single plug between them for the stator wire.
But both the 4 hole (95A) and 2 hole 130A 3G's have dual internal fans.
The charging cable from the factory was 8-4 Gauge depending on output.

The much more powerful Leece/Neville (185A) or Mitsubishi (210A) alternators that are found in ambulance chassis and the like, require a wider 8 rib serpentine belt to reach rated output.
Changing all those pulleys over is not really necessary for 99.9% of us

 

Novice trying to self-teach myself and thank you for the information. Found the two larger wires below the control wires.