Alternator case grounding.

[Mike65 475]

I am getting a 95A Ford 3G alternator to swap into my 69 Coupe & I have read on other forums about people grounding the case of the alternator to the engine block. On the back of the alternator there is a threaded hole I can use as a ground. My questions are, should I ground the alternator, & if I do what gauge wire should I use, & can I just use a wire like was used to ground the engine to the firewall like in the link?.

https://www.cjponyparts.com/cj-classics-engine-ground-strap-usa-made-1968-1969/p/WG1/

[RPM 1,190]

I just used a scrap piece of 10 or 12 ga wire and attached eye terminals to it. 

[pgold 2]

The CJ PONYPARTS part is designed to be OEM so probably rated at about 60A . I would install cable to match your alternator output , ie 95A. Same size cable from B+ to solenoid post and a matching fusable link is a good idea. 

[Mach1 Driver 560]

The alternator is already grounded to the engine through all the brackets. Make sure the engine is grounded to the chassis at the firewall with adequate ground straps. I would ask the alternator manufacturer what they recommend, and please share that with us- it would be informative. I will say that I don't see how putting a fuse link on a ground from the alternator to the chassis would help when there are still multiple paths through at least two brackets to the engine, then through the two engine grounds to the firewall. I'm just stating the obvious, not criticizing the idea. The fuse links need to be on the positive side, and depending on how you wire it you may need two.

[pgold 2]

I could have worded it better. Don't install fuse links in earth cabels. Put a fuse link in circuit with the new 100A 4GA cable from B+ alternator  to solenoid post              ( Battery side ). The mounting bolts may earth alternator but my new alternator came with earth bolt terminal and instructions to install earth strap. Removed alternator had earth cable to engine but definitely not capable 100A.      

Mike65 search 1G to 3G alternator conversion   Mach 1 Driver wrote a very informative post.

[Mach1 Driver 560]

Painless has a flexible braided 14" ground strap that is 1/0 and capable of 315 amps #40141

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=2ahUKEwid7ZHHgYvoAhVBSK0KHeWrBFEQFjABegQIBRAB&url=https%3A%2F%2Fwww.painlessperformance.com%2Fwc%2F40141&usg=AOvVaw3jrc9GyhyXmDHWRBiXDbcm

The charts I've seen for 12vdc for less than 5 feet of cable (they don't go shorter) with 3% voltage loss:

1/0= 250-300A

4 AWG= 100-150A

6 AWG= 60-100A

The Painless straps make quite a jump from 10ga to 1/0. Since there are usually two engine to cowl straps, two 10ga straps would be good for around 79A, but only one 1/0 is good for 250-300A, per that chart.

[GypsyR 32]

Over the years I've fixed a couple of Fords (and one Dodge) that no one else could with a store full of alternators by simply adding a ground wire from the case to the ground point where engine block ground strap is. Or is supposed to be. You'd think it would be grounded by the bolts and brackets but in at least a couple of cases it was not and I proved it. After the second one I fixed it became my habit to add a ground wire to every alternator I owned that didn't have one already.

The last one I caught I had since learned about voltage drop testing and was able to isolate the trouble area. Out of curiosity. It was between the case itself and the steel bracket. The aluminum case can develop a surface oxidation that apparently won't conduct electricity. Just like a coat of paint.

Do you NEED a ground? Probably not. I've seen hundreds of vehicles that didn't have or need one. But I've seen it be an issue a couple of times and ground straps are cheap. It's not going to ever be an issue on MY cars.