91' 4 0 2wd, ext cab

I won't be doing the add-ons yet but will be in the future and I've noticed a trend of people mentioning that the ranger is nearly at its max on electrcal load from stock. Looking at my favorite green label store I've found a 150 Amp alternator that fits and am considering it.

My thoughts for the not too distant future are a small sound system, plenty of exterior additions for lighting, an e-fan upgrade, and whatever else comes to mind. So I'm thinking the 150 upgrade would be a good idea. Stock is like 80amp if I did my research correctly so i think it would be good to upgrade but ive never run into this issue before.

What do ya'll think? Anyone have experience in this?

The 150amp alternator in queation

 

As long as it fits your 4.0l system, I think 1991 4.0l still used the alternator as the belt tensioner, in 1992 and up the alternators on the 4.0l were different mounting and there was a separate belt tensioner just below it

Current 3 wire connector on alternator/voltage regulator is fine to use as is

In 1991 charging system there are two 60amp Fuses(#3 and #7) in engine fuse box used for the two wires on the B+ alternator terminal, the stud/nut terminal
So you are OK up to 100amps as is
Currently you might be using 40amps with stock electrics at highest demand, every thing on, power windows going up and down and fan on HIGH

AMPs are "demand" current flow
i.e. a 150amp alternator DOES NOT produce 150amps, it "can" produce 150amps if demand is for 150amps
So the new 150amp alternator will produce the 40amps you need now, assuming it works, lol

When you add things look at a the Watts they require and you can change that to AMPs, or some devices will have AMPs listed

Alternator's AMP rating is when engine RPMs are at 1,800 and up.............at idle, 750rpms, the AMP rating is 60% of that
80amp alternator will produce a max of 48amps at idle
150amp alternator will produce max of 90amps at idle

So keep that in mind as you add things, you will have plenty of "headroom" to add electrical devices, but any devices, like sound system and cooling fans need the AMPs at idle


Just as a heads up
Headlights dimming at idle means 1 of the 3 Fields in your alternator has failed, so it has lost 1/3 of its power generating capacity, so 80amp alternator is now 54amp, and can only produce 33amps at idle, so lights dim until engine RPMs increase

 

Thanks for the input, super informative as always. If I do the upgrade later on I'd have to keep in mind the two fuses and swap them up to something (appropriately) stronger.

I've got many other things to worry about before I get to that point but thats why i look ahead.

 

You would want to use 1 larger gauge wire with a MEGA Fuse, 175amp, from B+ to Starter Relay post, the post with Battery Positive cable on it
But thats when you need to do it

You should NOT change the 60amp fuse to larger amp because the rest of the wire and that fuse box are not rated for larger fuses, so the fuse would no longer be that part that "blew" if there was a voltage spike

The point of all fuses is that they are the "weak link" in the circuit wiring
i.e. say the wiring for a circuit can handle 20amps, so a 15amp fuse is used, so if there ever is a short or voltage spike the wire and connectors do NOT melt, the fuse blows/melts

If you put in a larger amp fuse in ANY circuit, the wires and connectors then BECOME the fuse, the "weak link", lol, and never very good results with that setup, smoke shows