Are electronic and mechanical voltage regulators interchangeable on these trucks? Are there any compatibility issues beyond the general? For example, the original setup on these trucks was a 3 wire alternator; currently the truck set up is 5 wire…

 

The ground isn't counted so it is really only a 3 wire or sometimes called a "1G" alternator. There were only 2 ways the OEM alternators in a 73-79 F-series were wired "with gauges" or with "Idiot Lamps"

 

There is the Starting/charging system where the voltage regulator is part and then there's a Electronic or Mechanical ignition systems.

 

On alternators that DONT have an internal voltage regulator, which I assume my alternator is, can the externally mounted voltage regulator be EITHER electronic or mechanical (point based) or is there another factor to consider when purchasing a new one? Currently mine is mechanical (points based).

 

Sorry brain was elsewhere on this :-) Mechanical voltage regulators suck. They have contacts points inside. As they get older they become unreliable. Ford dumped them and went electronic.

Electronic can be much more reliable if you get a good one. Buy a Motorcraft unit. None of them work properly unless grounded properly. The mounting bolts to the body tub must have clean bare ground to the body and the battery negative must have a clean ground to the body in order for the regulator to do its job.
How did your continuity tests turn out from here ?

 

Appreciate response! Will pick up motor craft VR. Continuity tests don’t make sense. The last two have no continuity, and yet, while the battery (engine off voltage between 13-14 volts) is now new, and alternator (5 point connections) is also new, charge applied to battery was a highly erratic and constantly varying 16.55-17+ volts, way too high. I was surprised it was getting a charge, the old battery and alternator were deemed bad, but having no continuity on those two lines I figured battery would get zero.

The bad part is that, according to my best parts guy, there are no available alternator/voltage regulator/battery/ ignition wiring harnesses on the market unless I buy the entire wiring harness for the truck, including if I convert to that 1g or 3g single connector alternator. I’ve stripped the sheathing off the entire offending wire harness, it does have non replaceable, ancient looking inline fuseable links, and unidentifiable inline “cylinders” , so my repairing the existing wire harness seems problematical, unless I build my own out of a similar gauge wire using appropriately rated fusible links, connectors and plugs. It bears more research, without assistance from the parts community (Napa, autozone, o’Reilly’s) so….

 

To replace the fusible link look at the smallest wire diameter in the protected circuit, figure the length that wire runs, then read a simple chart to determine what the maximum current it supports. With a slow burn Maxi fuse or circuit breaker, that's your fuse size. You are simply reverse engineering it. This is also how you would determine what size wire to run when adding a circuit to a truck? You can reference any marine or rv book regarding wiring.
There are two fusible links that are suspect here and that would need to be sized in order to replace them with a modern alternative. The rest of your harness seems reliable. Right ?

Example can be found here ...

 

I have had no problem replacing these with the later electronic version used all the way to 1991 Diesels.

GR-540 is the part no. As long as the case is grounded they seem to work fine.

 

The cylinder you speak of is just a splice. The Motorcraft elecronic was a universal regulator and would fit a gauge type circut or a red light circut. Never had any trouble with one. RedRoad posted diagram. You may be able to find used harness from seller here on FTE in classified. Don't mean to sound like a Parrot but try to find a FORD shop manual, not a Haynes or Chilton's but a Ford. Usually printed by Helm. Printed, not on the cloud or cd or mp3. Sorry for rant.