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This is a very popular subject and upgrade, in the spirit of different ways to skin a cat this is how mine is going.
This is the first upgrade to my 80 F250 351M. In the attempt to get it drivable, it was discovered the original ALT wasn't cutting it. 11.75A at the battery at idle. I didn't bother trouble shooting anything after that because I planned on doing a 3G anyway. It could have been any number of things, the plug wires were literally falling out of the regulator plug as I was pulling things apart. The engine compartment looks like a rat's nest of wires, a previous owner obviously had a highspeed stereo system and perhaps a trailer or camper. I'll spare the nitty gritty details of what's needed, it is outlined on numerous threads on FTE and elsewhere. This page https://www.garysgaragemahal.com/3g-conversion.html has some pretty good details. It actually clued me into the need for me to put in a choke relay as mine has a 12v Edelbrock choke.
This is what I started with. I pulled the alternator of the mount to see exactly where everything was hooked up.
I think this mess pretty much speaks for itself. the rest of the engine compartment looks pretty much as bad.
I bought an alternator off Amazon and found this loom on ebay. The loom is already assembled and would cost about the same as sourcing the parts myself and having to put them together.
Since I have to put in a choke relay I spliced in a lead from the stator for that. I have plenty of slack since I plan to put a Taurus under hood relay and fuse box in down the line.
Here it is all plugged into the the back of the alternator. Note I removed the cheap crimp splice on the I wire. I'm using weatherproof, self soldering, splices for everything.
Swapping the pulleys. The easiest way to spin them off and on is is with an impact wrench. Don't forget to put one of the washers behind the pulley as a spacer. The mounting bolt for the 3G is M8-1.25, I bought a 25mm long one but could have gone longer as I used a split washer.
I tried to get it all in yesterday but the wind, cold and/or rain wasn't cooperating so I'll give finishing up a go today
Don't forget to list what 3G alternator you bought and or what application it is for. Then we will watch what modifications you need to make to fit it in the bracket. That is the most asked question. People use different 3G alternators and each one needs different modifications to fit physically, but the wiring is all the same.
Don't forget to list what 3G alternator you bought and or what application it is for. Then we will watch what modifications you need to make to fit it in the bracket. That is the most asked question. People use different 3G alternators and each one needs different modifications to fit physically, but the wiring is all the same.
This is the one I bought, I found it by searching from a list of compatible part numbers from another 3G thread. The only modification I made to the mount was straighten the lower arm a bit, just stuck it in a vice at the bend points and pushed them straighter. I needed to get a slightly shorter belt to keep it from bottoming out as well.
I would like to know the link to the wire harness.
Also that smaller yellow wire on the larger red I take it is a fuse link wire or do you still need to have a mega fuse wired in the system like factory did on the 3g ALT?
Also on the shunt is that part of the old harness that was pulled or is that still in the truck?
That is the only thing that I cant seam to wrap my head around just where it is for needing to bypass.
Dave ----
I got it all hooked up and running 14.6+v at idle across the battery terminals and to the choke. You can actually watch the choke open, I had to adjust it way over to rich to keep it running to warm up, it was way lean before and ran rough while warming up. All the slack is to give me room for when I put the under hood box and relocate stuff if I have to. I'll split loom everything once I get everything all sorted and cleaned up.
I would like to know the link to the wire harness.
Also that smaller yellow wire on the larger red I take it is a fuse link wire or do you still need to have a mega fuse wired in the system like factory did on the 3g ALT?
The seller says it isn't a fusible link but that's the only thing it can be, whoever answers question obviously wasn't too knowledgeable. . I have it just hooked up at the moment but I have a Mega Fuse and I might just put that in.
Originally Posted by FuzzFace2
Also on the shunt is that part of the old harness that was pulled or is that still in the truck?
That is the only thing that I cant seam to wrap my head around just where it is for needing to bypass.
Dave ----
I believe that is the Yellow/orange wire coming off the battery. i just left it alone as i just wanted to get everything hooked up. I have no idea if it even matters.
Good to hear you got it installed the it works. I would of also thought that yellow wire would have been a fuse link why else would you add it to the end?
I see writing on the wire is there not enough to tell what it is? If it is not a fuse link then why add it??
On the shunt I dont know if anyone has ever run a 3g and left it in place and if so the out come?
I think they say it cannot handle the load (amps) but also wonder how much it can handle or did they figure if max amp output of 70 of the old ALT's that is what they set the limit to?
Thanks for the information
Dave ----
On the shunt I dont know if anyone has ever run a 3g and left it in place and if so the out come?
I think they say it cannot handle the load (amps) but also wonder how much it can handle or did they figure if max amp output of 70 of the old ALT's that is what they set the limit to?
It's still in place. The shunt is still feeding the truck's electrical like it always did. He said he cut and taped off the original alternator orange/black, so the new alternator is not using the path of the shunt, the new alternator has it's own wire in the new harness he bought to the battery.
If you want to think of the electrical as a bunch of little guys running up the wire, they are running up the new wire from the new alternator. They run up to the battery + connection where they have a meeting at the battery, and divide themselves, part of them running to the battery, and the rest of them running down the factory wire with the original fusible link, through the old shunt, and then into the cab to power the truck.
As long as excessive loads are not tied to the original wiring inside the cab, then the shunt can handle the new alternator. The problem would arise if you tried to use the original old alternator charge wire. This does go through the shunt, and besides the old wire being too small for the new alternator, the shunt would have to handle the charge current from the new alternator and it would be too small.
He did mention he is going to add a aux fuse box. If he ties this new aux fuse box to the battery directly, then he can put added electrical loads in this box, and utilize the full output of the new alternator, leaving the trucks factory wiring alone.
The issue with the AMP meter is it no longer reads correctly.
When the truck was original, key ON - engine not running, if you pulled on the headlights on the amp meter would show a discharge. Adding more loads causes the needle to move more to the discharge side of the amp meter. The battery is the only source of power, and is being drained.
Now the alternator output is connected to the battery. Some of the amps go into the battery, until it charged up.
The remaining amps the alternator produces goes to the fuse box. The current direction through the shunt wire is the same as if the battery was the only source of power. So the amp meter shows a discharge
So after the battery is fully charged, the AMP Meter shows "amp output" of the alternator, in the discharge direction.
It's still in place. The shunt is still feeding the truck's electrical like it always did. He said he cut and taped off the original alternator orange/black, so the new alternator is not using the path of the shunt, the new alternator has it's own wire in the new harness he bought to the battery.
If you want to think of the electrical as a bunch of little guys running up the wire, they are running up the new wire from the new alternator. They run up to the battery + connection where they have a meeting at the battery, and divide themselves, part of them running to the battery, and the rest of them running down the factory wire with the original fusible link, through the old shunt, and then into the cab to power the truck.
As long as excessive loads are not tied to the original wiring inside the cab, then the shunt can handle the new alternator. The problem would arise if you tried to use the original old alternator charge wire. This does go through the shunt, and besides the old wire being too small for the new alternator, the shunt would have to handle the charge current from the new alternator and it would be too small.
He did mention he is going to add a aux fuse box. If he ties this new aux fuse box to the battery directly, then he can put added electrical loads in this box, and utilize the full output of the new alternator, leaving the trucks factory wiring alone.
The one I was referring to is still actually active. It still goes to the cab, I'm guessing I should disconnect it and tie it off then. I just didn't mess with it because I was rewiring other stuff and the ring wasn't large enough to put on the solenoid post. I thought it was a second cab power line.
I have nothing that is putting hardly any load right now, not even a radio. I just got this over with because it was going to happen anyway and I was going to do a MkVIII fan.
The wire I tied off is the Ammeter wire I think. I'll have to rewire it after I get my Volt gauge.
I was thinking the same thing but with the rest of the under hood wiring and him saying this was a start to fix it all I just left it be 
