89 F150 lariat xlt here. I recently fixed the ac/heat and I've noticed at night if I have the headlights on, the ac, and maybe a blinker or windshield wipers or whatever the voltage will drop significantly and the truck will even die at a red light or whatever unless I give it some gas. I'm thinking maybe I need a better battery but I thought I would throw it out to the hive mind and maybe there's another reason for the voltage drop. Thanks ya'll.

 

 

Keep in mind the factory 2G alternator puts out very little to no power at idle/low RPMs. That's a design flaw. Highly suggest you upgrade to a 3G to fix your current issue and prevent the flamethrower 2G from claiming another victim.

 

So I just checked the battery with a voltmeter and I got 12.6 and when I start the truck I've got 14+ so I don't think it's the battery. Must be the 2G alternator. I'm looking on Napa's website now and I don't see them labeled as 2g or 3g so I'll give them a call and figure it out. Thanks ya'll.

Napa alternators

 

The factory replacement alternators listed for your truck are all 2G design. Everything you wanted to know about the 3G upgrade: https://www.fullsizebronco.com/forum...ins-agian.html

 

That's very helpful. So I see mine is only capable of 75 amps and the 3g is upwards of 100-150. So that link tell's me everything I need to know except where to buy one.

 

 

Order an alternator for one of these:

(1994-95) Ford Mustang 5.0L
(1994-00) Ford Mustang 3.8L
(1994-97) Ford Thunderbird, Mercury Cougar 3.8L
(1990-95) Ford Taurus, Mercury Sable 3.8L
(1993-99) Ford Taurus, Mercury Sable 3.0L
(1995-98) Ford Windstar 3.8L & 3.0L
(1991-94) Lincoln Continental 3.8L

 

Do the 3G upgrade, totally worth it. Installed a 95 mustang v6 alternator rated at 130 amps. You gotta use an angle grinder to cut the bracket slightly to make it fit and fabricate wiring but it's not that bad. I was very impressed with the results.

 

I did exactly as above and all works great.

 

95 Mustang alternator is $168.00 at Napa.... yikes Napa Any way to field test an alternator at the junkyard? I wouldn't generally buy a junkyard alternator but in this case....

 

I bought mine from a guy who was replacing the V-6 with a V-8 to build a race car. I think I paid $30.

 

I'll give you $35 for it.

 

Soooo, when did they start putting 3G in F-250? I currently have a 91, that I am rebuilding, wondering about this upgrade.

 

Late 90s I think.