MS wrote:

In choosing the fuse, be sure to get one that has good, solid connections to the cable.  That is pretty much the only thing that separates the good from the Chinese bad.

Do modern cars use a megabigfuse? 

 No I don't think so, they use fusable links.
 For me I would rather have a fuse blow  than a piece of wire go thru a melt down.

Last edited by Rudi (3/21/2019 10:23 AM)

1fststang wrote:

Have my 3G alternator on and just need to make a few connections to hook it up. Have the pig tail that connects to the two plugs on the alternator, one wire to battery lug of alternator and one wire to harness to energize it.

Need a 175 amp mega fuse to run the battery cable to before the battery side of the solenoid.  Anybody recommend a good one or all about the same ?  plan to mount below the solenoid and run a short 4 ga cable to the mega fuse then another 4ga to solenoid.

any do's or don'ts with this upgrade ?

I built my own...purchased the Mega fuse, holder and cable lugs at Oreillys.  I think I got the cable at Lowes....here's a pic for reference....

 

One of the things a 3g does well, is sensing voltage needs at low revs.
It doesn't do that anywhere near as well when the yellow sense wire is just looped to the output terminal.

Its the myth of the one wire alternator.  It allows for one wire hookup, but that simplicity comes at the cost that the alternator has no idea what's really going on in the cars electrical system because all its "seeing" is its own output voltage.

The yellow wire should be connected somewhere downstream, ideally to a circuit that can be highly loaded.  The main power feed in the dash is a good spot. 

PA performance has great ways to get the fuse installed, and then tie in your 3G alternator to still trigger the ALT light if it goes out.

I have that setup myself
 

I agree with Walt. I have the yellow wire connected to the slternator end of a 6 gage wire that goes to the solenoid.  My alternator charges fine with no issues. I agree there should be negligible voltage difference, and that this is not the best way to wire it, but there is one less wire involved now. If it works like that, I see no reason to add a signal wire. Maybe I am just in the stage of euphoria since my system is actually charging quite well vs anything I ever got out of the original alternator.  I do believe most of my former charging issues were caused by the crappy aftermarket replacement wiring and plugs rather than the type or capacity of the alternator.  I can now run headlights, fog lights AC and stereo, along with a powerful ignition system and the voltage gauge reads 14 volts all the time.

TKO’s suggestion to run the yellow wire to the ignition switch makes more sense, but I am at the ABDFI point in this installation!

Speaking of charging, I will be posting in the tips/how to section on how to convert a Mustang AMP gauge so it actually measures rate of charge rather than just taking up space in the dash.  It involves gutting a Stewart Warner gauge AND a Mustang Amp gauge and making a gauge that is indistinguishable visually from the original, but performs as a Stewart Warner ammeter

My car is a 1967 Mustang Fastback

I'm using speed hut gauges and have their voltage gauge. No factory amp meter or anything to worry about.

I also have the American Autowire harness but yet to start install.

I have a March Serpentine belt system on the engine so hopefully no belt squealing.

I'm planning to get my electric fans in place and mostly wired as well as msd box etc then start the new wire harness install.

Seems like most of the info on the net says use 175 amp fuse,   I'll do some research on battery cables and try and get some good ones.
 

I would caution anyone running the yellow sensing to the ignition switch. Especially anyone using original wiring. The regulator is used to maintain proper battery voltage not system voltage. With older smaller gauge wire and old connectors, there could easily be a 1.5 volt difference between the battery and the ignition switch. If you try to maintain 14 volts at the ignition switch you may be overcharging the battery. 

Bolted, I agree # 6 from the alternator is plenty and I've use wire barn for GXL wire. Good for the heat under the hood and for soldering. I'm going to try your HiPo alternator pulley suggestion if I can find one.

MS, I don't know what your charging issues were but would agree, the issue was probably not a smaller older style alternator. The only real draw these old cars have on the alternator is recovering after start and a large stereo upgrade. I don't think you really NEED a large alt until you install a pair of electric fans. And we all know you don't have those. BTW interested in this amp meter upgrade.
 

Good suggestion on the GXL insulated wire.  I only use GXL from Allied Cable.  It doesn't "crawl" away from solder like the Auto Zoo crap.

BB
 

I ran the yellow sensing wire to the starter solenoid. I agree there won't be any appreciable voltage drop, but my thinking was I want the alternator to maintain voltage at the main power hub.

I use a 150 amp mega, 175 seemed like if I got to the point of blowing that I'd have bigger issues by then.

I have yet to install it, but I acquired a volt guage from rocket man-
https://www.rccinnovations.com/index.php?show=menu-volt-all

MS wrote:

In choosing the fuse, be sure to get one that has good, solid connections to the cable.  That is pretty much the only thing that separates the good from the Chinese bad.

Do modern cars use a megabigfuse? 

Late 90s trucks used them @ 175A

 

Also the Taurus from 96 with a 3g used a 175a ... don't know why ... it's above my pay grade.
It only protects the car from the alt in case of multi diode failure. .......  I think.