BroncoII4x4.com

My '87 B2 with 123,000 miles seems to have a weak alternator and electrical system (battery is fine). When the revs go up a bit, the headlights get significantly brighter, and the window motors work faster etc. than when at idle.

I was looking at the 40W, 60W 100W and 140W alternators available through LMC Truck and wondering if installing a 100W alternator would kick-up my overall electrical system performance? I will be replacing my old radio/cassette unit with a new CD player in the next few weeks, but do NOT have a loud system, and no electrical extras. Also, if I installed a 100W alternator and a high voltage coil, might I expect any noticeable or measurable performance improvement? In either power or gas mileage?

Any insight appreciated. Thanks.
CraigK

There is no reason to get a high output alternator. Your stock one is just bad. One of the diodes is burned out for the low RPM circuit. It's not charging at idle at all. Most auto parts stores will test your charging system for free. No need to remove the alt or anything.

I have the same low idle/volts drop syndrome on an F 150, 1993.
Is this diode something that comes in an alternator rebuild kit?

I would assume no. I think rebuild kits are probably just bearings and brushes, but I've never rebuilt one, so I don't know for sure. I always just get one at pull-a-part for a few bucks and forget it. It's not for sure the diode, so you would want to have it tested.

The 3G swap is popular in the EB world. You guys might want to research that a bit.

Whats the " 3G" and "EB" ?
Not familiar with the terms.

3G is a generation of alternator. http://www.fordfuelinjection.com/?p=75

EB is Early Bronco, 1966-1977

Thanks, good info!

The advantage of a higher amp alternator is that you can run more accessories and the alt will stay up will the demand. Such as 100 lights, winches, stereos, etc. If you run these items that draw alot of juice they will drain your battery pretty good. I used to a big bass amp that would dim the headlights at full peak of the amp. That is when i had to up grade.

Nobody - You posted it's possible (likely?) that just a low rpm diode circuit is burned out. Is this something that is included in the "alternator voltage regulator" unit that bolts to the back of the alternator?

If so, it looks like this can be purchased by itself, for as little as $25.

CraigK