620 Alternator Swap (FN style to LS style)

[Spawn]

I'm hoping that someone here might be able to help me out with regards to upgrading my 1977 620 alternator & external voltage regulator from the current 35A with an FN style connector to a 1980's 720 internally regulated alternator that outputs 60A with an LS style connector (it's a NIB Duralast 14303 that came with the truck & parts when I bought it).
From what I can gather I think I need to connect the S terminal of the T-connector to the BAT terminal which goes to the + terminal of the battery. Then the L terminal of the T-connector needs to connect to the CHG wire which goes into the dash I believe.
What I'm wondering is how this relates to the FN style T-connector, and how to eliminate the external voltage regulator? I don't want to just take out the 35A alternator and directly replace it with the 60A unit, as I am afraid that if I wire it up exactly the same way as the 35A is currently wired, that I might damage the 60A alternator, or that it might not actually charge the battery because of the external voltage regulator (which I think may be bad as the 35A alternator tested good at Advance Auto).
Can anyone who is familiar with this swap/upgrade provide me with some detailed instruction on how to perform this work without causing any damage or issues with the setup?  :confused: 
Thanks in advance!

[sebpv]

did u try google? There are many ways of upgrading to IR alternator shown for this truck

[Spawn]

Yes, I have looked, but I haven't found anything very specific or detailed.  There seems to be a lot more information for upgrading to a Saturn CS130 alternator, but I don't have that alternator as an upgrade.

[kelowg]

u need to jump two sets of regulator plug wires. But i dont know which ones on 620. this is reguardless which internal reg alt Ur using. jumpers gets the charge light to work.

[banzai510(hainz)]

its more than that if you have a L16 motor as they use the smaller bolts in the mount and the holes on the later for the later years. They use a bigger type.

I went back to the stock 35amper as it fit better an stopped having broken bolts shearing in the block.

also the idler arm mount the bigger alt will hit and need a smaller belt I think.

 

just use what you got and learn to drive will less stuff on

 

http://www.amazon.com/INNOVA-3721-Battery-Charging-Monitor/dp/B000EVWDU0

[thisismatt]

This is for the 510 but they should essentially be the same as long as you correctly identify the charge light and sense wiring at the ext. regulator. The easiest thing to do is lop off the pigtail from the ext. regulator, pull out the unneeded pins and crimp/solder the two pair you need together. That way you don't modify the harness at all, or you can open up the regulator and do it all internally for a fully stock look.

 

[datzenmike]

Unplug and remove your external voltage regulator. Trim the wires off at the regulator and keep them as long as possible to the plug side. Take the plastic plug with the trimmed wires and join and solder the solid White and Yellow together and the White/Red and the White/Black stripe wire together. I removed my wires from the plug but you can do them with them on.  I also used heat shrink tubing but electrical tape or Marrette connectors will also work. Not as neat looking.

 

 

620 plugs vary over the years but push out all the other pins and their wires as they are no longer needed and you don't want them touching anything.  Your plug should look like this when done

 

 

Now just plug this back onto the truck's wiring harness. Neat and no loose wires to touch.

 

You are about half way done.

 

The 620 has an electric choke and this modification permanently powers the choke relay coil even when the ignition is turned off. It doesn't draw much power, but I found over a weekend the battery is very low Monday morning. The simplest thing to do is unplug the relay but this would then not warm the choke heater and turn the choke off when running. What I did was disconnect the choke relay and find another power source for the choke heater that is turned off by the ignition. Luckily the idle cut solenoid is right beside the choke heater on the Hitachi carb... simply join the Blue choke heater wire to the Red idle cut solenoid wire and you are finished.

 

 

If you are not running tor electric choke just unplug the electric choke relay.

 

Before I forget, test fit the 720 alternator first. I found the 50/60 amp internal regulated alternators were a very tight fit in the 620. They tend to hit the top of the idler arm. On the 720 the idler arm is on the outside of the frame.

[DanielC]

An alternator voltage regulator does not know, or care how many amps the alternator puts out.  The voltage regulator measures the voltage only.  Nissan alternators, and voltage regulators are very reliable.  Internal regulated alternators are not better, just different, and cheaper for car makers, because one less part,

 

Because of the electric choke using the wiring of the external regulator wiring, I would keep it that way.  Just get a 50 amp Nissan alternator.

[abbylind]

I installed a 77 200SX 60 amp alt in my 77 620. Used the existing voltage regulator...simple plug and play. Built a new upper alt bracket and a 1/2 longer fan belt