Have a alternator and regulator coming from Autozone later today, they had to get it from the warehouse. Trying to get a good friend that is good with electrical over to help prove out the alternator harness and try to sort the lack of power to the carb solenoid wire. So if this all proves good can I run it with the bad amp gauge still installed?

 

Yes can run it the bad AMP Meter.
If you are planning on switching to a volt meter, I would remove the small red and yellow wires from the shunt when you have it all opened up. This will make it easier when you get the volt meter installed.

Something forced to much current through the AMP Meter, so look closely at the splice points where the red and yellow wires attach. Make sure the shunt wire isn't hanging by a few strands of wire. A weak connection makes the AMP Meter path a better choice.
Jim

 

My concern about running without a amp gauge is that I would have to pull it to send to rocket man for conversion. Will it is out the connections on the hard shell connector to the cluster would be open and not completing the circuit. Would that cause a problem.
So if I understand correctly, the shunt wire is a resistance wire that provides a measured amount of voltage so that the amp gauge will work. Now if I test the wire with a volt meter what number should it be? The red and yellow wires out of the three wire plug both are connected to the 10ga black wire that is connected to the alternator, the both appear good and no burnt marks or swelling I'm thinking they are good. Yeah looks can be deceiving that is why they will be tested.
This all started when the MSD box blew a capacitor and two diodes, must have sent a power surge through the electrical system, so beware if you have one of there boxes, it's a matter of time, mine lasted 30 years

 

Have you picked a direction, AMP Meter or Voltmeter ???
Its really to separate conversations.

I will start with the AMP Meter, meaning you are going to install your spare part and leave it stock.
It is fairly obvious to me the your current set up is faulty. If it was working correctly your AMP Meter wouldn't be pegged to the change side.
The system is design to split the current 60 to 1. I think yours is closer to 20 to 1.
The gauge will over range by about 50%.
So when the MSD died, it caused a very large AMP draw, the alternator try to cover this by going to max output. The current surge went through the Shunt wire, towards the battery, meaning the AMP Meter went in the charge direction.
If the engine RPMs where high enough the alternator would produce 40+ amp. This should have not caused any damage to the AMP Meter.

Can you actually see the splices on each end of the shunt wire or are the covered in a rubber cylinder shaped water proof covering.
Others have had to cut the rubber off to exam the splice underneath and found most of the wire strands broken. Not something you can see without digging deeper.

There isn't any way to test or calibration the system, it falls into the "magical" category.
There isn't anyway to make the alternator charge the battery at a 30 amp rate to test calibration.
Here's a link to the 79 bronco thread, where he is trying to make his own shunt.
https://www.ford-trucks.com/forums/1...l#post21698654

I will address the voltage meter in my next post.
Jim

 

Here a photo of the black rubber splice covering.
The red wire is one of the AMP Meter shunt wires.
The larger black wire is the Shunt Wire. On the right.
I am not sure if its the same for 1972, most of my experience is with 1980 to 1986 trucks.
Jim

 

If you have decided on switching to a VOLT Meter, just cut the red and yellow wires a few inches from the splice joints and tape the well.
Pull the red and yellow wires back towards the 3 wire connector, you will not need these until you get the new volt meter installed.
You can also remove the bad AMP Meter, as there is no power going to it anymore.

Also, you won't need the original shunt wire anymore. It might be worth considering upgrading the alternator wiring harness with a large gauge wire. Ford was always trying to save copper, by keeping the wiring sizes as small as possible.

Good luck, Jim

 

Wiring in truck
Out of the three wire plug there is a large black/yellow straight to the aletnator. In that wire there is a three way connection (no rubber ball) with a large black and a small yellow wire connected. That black wire runs back to the solenoid and connects to the fusible link and the red wire out of the three wire plug. All wire are fully stranded at the connections.
My thought is to install alternator and regulator leave wires untapped and verify it is charging. Next remove burnt amp gauge and replace it with a spare and send burnt one to Rocket Man for conversion. Still need to find a 12v switched wire to replace compromised red wire from switch that was used for the plus side of the coil originally but was used to power the MSD
Thoughts???

 

Refresh my memory, please. The compromised red wire from the ignition switch is melted underneath the dash? Or burned under the hood?
And is it red with a green stripe, or purely red? Was any of it a pinkish brownish color, and wrapped with a heat resistant fibrous coating?
I don’t remember seeing pictures of it in this discussion, but I’ve been reading so much lately, sometimes I can’t remember which discussion is which!

Do you happen to have any pictures of the back of the ignition switch by any chance?
I’m trying to bring myself up to speed again, because I thought that the compromised wire went to the ammeter, and not the switch.
Time for me to reread from the beginning, I suppose!

 

the compromised wire on the switch is the red/green and went to the positive side of the coil and has issues under the dash and hood, insulation kinda melted. The red / green wire is also connected at the same terminal as the brownish pinkish ( wiring diagram says violet) with the heavy insulation
No pics added as I am not savy enough to do it. Could take them and send to someone to post?

Alternator and regulator installed, fired truck and volt meter shows 11.87 across battery, not running show 12.14. what the heck?

 

With the engine OFF, key OFF.... can you measure 12.14 volts on the large alternator output wire?

It's possible the fusable link took some damage when the MSD bos shorted out internally.
Jim

 

Below is a copy and paste from the first paragraph in post 50
I am not sure if you checked this.


The voltage regulator also has an "S" connection. On your truck, with an AMP Meter, this is the source of the input power needed to bring the alternator online. All ford G1alternators need an external KEY ON power source to come online and produce power output.This is usually a green wire.I believe this power source is shared with you damaged wire on the ingition switch.

Jim

 

Yes the large wire on the alternator is reading 12.14 and the fusible link was replaced.

No green wires at all on the ignition switch. There is a green / red wire from the S terminal on the voltage regulator that runs to the 2 wire plug by the ignition solenoid but my wiring schematic shows it goes to the top rh pin in the large cluster plug and is for the amp gauge. There is a large black / green wire on the ignition switch which goes to the 4th rh pin on the cluster plug which my schematic shoes to be for the brake light warning switch

 

 

Does the green wire on the voltage regulator have key ON 12 volts?

 

That’s not out of the ordinary for readings when the alternator is not charging.
When the engine is running, and there is electricity being used, the battery reads slightly lower than when everything is off.
So that 12.14 was your battery’s natural state at that point.
The 11.87V was the battery in use, but with no current coming back into it from the alternator.

And just out of curiosity, because I’ve forgotten yet again if this is a 70 or a 72 truck (oh yeah, a ‘72 it’s in the title!), do you have just a simple modern voltage regulator on the fender skirt?
Or are there multiple components to the regulator, mounted over on the radiator core support, in that front corner?