'81 720 Alternator mystery

[Survivor]

Hello all! Sorry if this info is already covered here, but I've been looking on and off for days now......

 

I own a '81 720 kingcab pickup, bought it for $500 10 years ago, use it as a ranch pickup and backup commuter. A couple weeks ago I started suspecting I was having charging issues, a complete inspection of the system confirmed it was the alternator.

 

After picking up a new(stock) Alternator, I set about taking the old one out. As I was removing it I noticed that the bracket had lots of non-stock parts in it...weird. Once I had it out, I compared it to the new(stock) one, and shockingly the two alternators are different!!

 

The old alternator had one arm to connect to the lower bracket, the new(stock) one has two, hence the extra parts on the old one. But the most important difference is where the sense and field wires connect to the alternators.

 

The old alternator has a plug that looks like -> [-- --] , the new (stock) alternator has a "T". I suspected its a GM alternator, since the guy I bought the truck from was a retired Goodwrench mechanic , comparing it to my dads Chevy confirmed the suspicion.

 

My question is which of the prongs in the "T" on the stock alternator is sense and which is field? Its not marked??

[DanielC]

I assume you are putting a Nissan alternator back on the truck. Here is a site that might help you.

http://www.dimequarterly.com/

On the left side frame of the site, under technical, click on electrical.

On the right side window, click on Wiring Diagrams.

in that window, scroll down to "SIMPLIFIED START/CHARGE WIRING DIAGRAM"

There are two diagrams. the bottom one is for internal regulated alternators. It has two plugs beside the alternator. You alternator might match one of the plugs.

[Survivor]

Thanks Dan!

Shortly after posting this thread I found a website discussing converting older Datsuns with external regulators to internally regulated alternators, I got the right clues there.

 

The "S" wire(the larger solid white) goes to the top of the "T", the "L" wire(the smaller blue striped white wire), goes to bottom of the "T".

 

My truck fired up and is charging at the correct voltage, success!!!!

 

Maybe I should do a "How to" thread on adapting a GM Alternator to the Datsun 720, had I known what it was to begin with I'd have just got another GM(probably lots cheaper and easier to get).

 

Thanks to all who looked!

 

EDIT: Now that I got the Alternator dealt with, and did both sets of Ball joints, the Tranny sync went out this morning! LOL!! I can't win! I need to find that 81-82 720 4x4 with a blown engine that must be out there...........

[desert skipper]

Thanks to all who looked!

 

EDIT: Now that I got the Alternator dealt with, and did both sets of Ball joints, the Tranny sync went out this morning! LOL!! I can't win! I need to find that 81-82 720 4x4 with a blown engine that must be out there...........

 

 

If you find the "pieces parts truck" out there let me know if it has any good front axels assemblies.

Thanks for the cross breed info.

 

edit - edit

I found Nissan parts that are "no-longer avaliable" from several sources. My front axel is back rolling. :thumbup:

Ironicly . . . . my oil-filter change last week developed into diagnostics for a no start. I fumbled the wiring

and pulled the starter harness off. I didn't know that untill a local wrench found the loose wire.

During the oil change I heard crackling around the back of the alternator and found a "loose" wire.

It was still in place but not making secure contact. I repaired the connector and finished the filter.

When I "attempted" to start the engine for leak-check, that's when I found the no-start condition.

If anyone is looking for 4x4 parts I have a list of sources, maybe it could help you. Skip.

[datzenmike]

2wd trannys will work. They have slightly higher (lower number) ratios and a speedo output in the tailstock. I used a 2wd in my truck and just sealed the opening. Only factor is the length has to match.

 

'81-'83 200sx 5 speeds from a Z 20/22 motor will also. This is what I have. (the '82-'83 is an exact match for ratios)