I agree.

Alternator is bad and since it may have messed some stuff up, I would do the 3G upgrade as well since you are going to be redoing stuff.

 

The 3 wire connector has a FAT Black wire which is feeding power into the Cab.
The red and yellow wire are feeding the AMP Meter. If you follow the red and yellow wires towards the engine the will connect to the amp meter shunt, one on each end.
You could disconnect this plug and see if anything changes on the AMP Meter, I doubt it will, but I would still try.
If the AMP Meter doesn't spring back to the center position, it will have to be replaced. Changing to a VOLT Meter is an option, there's a link to a "HOW TO" in my other post.

If you do a 3G ALT upgrade you will lose your AMP Meter, as the SHUNT is bypassed with new larger wiring. Personally I would keep it stock unless you need more power for something.

While the charging system is not charging the battery or producing any power out of the alternator, it doesn't necessarily mean the alternator is bad. I like to troubleshoot first, some will replace parts first and then troubleshoot ... if replacing all the parts didn't fix it.
I would test for KEY ON power at the "S" wire on the voltage regulator.
The large output wire on the alternator, BAT, should have voltage all the time.
You can do a " full field test" on the G1 alternator also.

Jim

 

Have to the s terminal on the solenoid, as truck starts and runs. Disconnected the blk,ylw plug no change. Have a spare clutster I could pull the amp gauge out of and install. Would that be okay or do I need to find and fix the wiring first? Following the wiring out of that plug it goes into the harness which goes to alternator and across the apron towards the cab, don't see a plug where the shunt could be, anyone have a pic of the shunt? No need for a larger alternator as the truck is stock, gonna pull it and take it to Oreillys for testing
The fried wire out of the switch is the factory coil + side with the yellow boot, as I remember it drops voltage for 12v to 6v to prevent burning the points, odd it work for 30 years feeding power to the msd without a problem. Maybe the new boxes put out more power or somethig? Think what I can do is use the factory carb solenoid wire as a 12v switched wire to feed the box and not have to overlay a wire to the switch need to ohm it and see. Could the voltage regulator have taking a hit? Trying to get time to work on this thing and do some of the checks suggested, some I'm not sure on how to do.

thanks guys.... we'll get this

 

I would check the external voltage regulator on the firewall and make sure it didn’t burn up as well.

 

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.

If you want to find the AMP Meter shunt, you are going to have to remove the black tape on the harness. Follow the red and yellow wires towards the alternator.
The Shunt wire is not something that is removable, or replaceable, or has a plug on it... It's just built into the alternator harness. The red and yellow wires are just splice in, on each end.

I would inspect the splice points on each end of the AMP METER SHUNT, and the shunt wire, before replacing the AMP METER. It's getting harder to find parts... I won't not risk burning up another amp meter.

The MSD uses a small red wire as a trigger to turn on the ignition. This needs to be connected to a KEY ON power source. As the resistance wire is only 1.15 ohms, and there really isn't any substantial current flow though the small red wire, it should have worked fine.
The MSD has two large wires the run directly to the battery, which carry the heavier current flow needed for the ignition system. Did you wire it per the instructions... or something else?

It is possible that the MSD Box shorted out internally and caused all of these problems, I haven't read the all the posts from the start, so I am not sure of the chain of events that lead you to this point.

Good luck, Jim

 

Since the ammeters aren't a good indication of the health of the charging system, IMO, it is a good choice to convert the ammeter into a volt meter.

 

While I agree with this post, I also respect those who want there truck to remain stock.
I am going to add a couple of examples to illustration his point, regarding the usefulness of an AMP Meter.

I personally made the switch to a VOLT Meter in 2014. I wrote a HOW TO linked below.
The wiring changes are made in the engine compartment.

https://www.ford-trucks.com/forums/1...olt-meter.html


So, using your truck as an example, your MSD ignition system draws its power directly from the battery. So driving down the road with "ignition only" ... Meaning no headlights, no heater fan or any other electrical loads. The alternator is going to be sending about 5-6 amp to the battery to handle the MSD draw. This amperage is traveling through the Shunt Wire. The AMP Meter thinks it is charging the battery. The AMP Meter needle moves slightly to the charge direction. So the reading is currently faulty.
If the alternator fails, meaning no current output, the AMP Meter returns to its center position, which is also a faulty reading, given the 5 AMP discharge rate while driving.

I installed headlights relays, which feed the lights directly of the battery. With the engine not running, KEY OFF, pulling the headlight switch out caused the AMP Meter to move towards charge. Switching to Bright Headlights caused an increasing movement towards CHARGE. But how could it be charging if the engine is not running.

The AMP Meter needle movement is very small, meaning you will never see the change while driving when the alternator fails.... even on a stock original system, when driving in the day time without any additional loads
On a volt meter, If the alternator quits, the needle movement on a volt meter is very evident, over 1/4 scale. See above link for photos.

Your amp meter shunt is most likely damaged, which forced the current though the meter, instead of the shunt wire. This alone might force you to do wiring changes / upgrade the wire size between the alternator and the battery. Meaning your only choice is the volt meter upgrade. And I do believe it is an upgrade.

Good luck, Jim

 

The yellow and red wires from the C8 connector are the ones that operate the converted gauge. I did a 3G upgrade on my truck at the same time that I had the gauge converted.

 

Hey Dan, glad you finally found the issue. I know if can be very frustrating to drill down into electrical to find a small problem that gives big headaches!
Sorry you spent money needlessly too though, but if you look back here, you had almost all the information you needed to figure it out. A little testing would have proven where the fault was
So this is more for anyone with a problem like this in the future that might come across your thread. Sorry ahead of time if I sound preachy (as I tend to do!) or whatever.

Great info to put out there right up front.

Yes, assuming you jumped the starter relay/solenoid one way, and not the other. And the battery and negative cable are good too.

Here's the key info. There are only two (well, three if you figure individual wires) that can cause a loss of all this power. It's not the ignition switch, or anything in the cab.
The only things it can be are either of the battery cables, OR the main power wire to the cab. Usually via the fusible link.

Your test proved that the negative battery cable was good. You proved that the battery and starter were good. You also proved that the starter relay was good, if you simply jumped the battery side to the small "S" terminal of the relay. Which, by the way, if you did it this way, you also proved out that the positive battery cable was good. If you jumped it in other ways, a couple of further simple tests would have narrowed it down.
Leaving only the power wire and (most likely culprit) the fusible link.
Nothing in the charging system or ignition coil or distributor will keep the starter from cranking (unless the wiring is entirely fubarred!) and there are no other components that will keep power from getting to the cab. Just the main power wire and it's fusible link.

I've always tended to leave pulling tape off of wires to the last ditch effort department, which has bitten me once or twice over the years. I fought a suddenly dying engine, and a crank but no start condition for a couple of months before I finally dug into the ignition harness on top of the engine. Where I promptly found a bad splice that had gotten corroded and loose. Sound familiar?

Anyway, hopefully your discovery will help others. We've actually dealt with these exact issues many times here on the forum over the years. I would say that, probably 80% of the time it's one of the battery cables (loose, corroded, or deteriorated internally), but the other 20% seem to have been the fusible link.
Another potential fix for this type of troubleshooting, is to replace the fusible link with a fuse.
While fusible links have their place, and there are good reasons that the OE's still use them, I love nothing better than to easily see a blown Maxi-Fuse right there in front of me, rather than relying on the visible appearance of a burned out link (or hidden splice!). And trying to fix it on the side of the road is less of a pain with a fuse.
Speaking of "on the road" by the way, another thing we're glad of is that it happened to you right at the house instead of out in the middle of nowhere in the middle of the night!
Thank goodness for small favors!

Paul

 

Also, testing for voltage at the coil is not going to be consistent (or even possible sometimes) with a Capacitive Discharge system like an MSD6 box.
Not sure if that part was touched on in the last couple of pages, but for each spark event, the box imparts a short burst of 300v or so to the positive side of the coil, then instantly breaks the ground contact on the negative side.
So "seeing" voltage on the positive side with a meter while the key is on, might not be a viable test in most cases.

I think you said you found some faults with the wiring at the switch as well, and certainly with the box, so all your testing and digging paid off. But the voltage test is a weird one and tends to give inconsistent clues, when it comes to a CD ignition.

Paul

 

Changing to a volt meter is an interesting idea, have to send the gauge to rocket man and his turn around in Feb 11, thats a long time. Is it possible to ground the yellow wire and run the truck with out the amp gauge installed, or how to run the truck without ?
Has anyone purchased shunt wire and repaired a harness? Have a spare 71 cab and it had the alt harness still attached , with a little love I believe it could be used, not sure how to test or verify if good.
Also the blue switched wire with the female white bullet connector on the firewall is not hot when off or in the run position. Should be hot in run mode as I used same wire on a 70 Mustang to power my MSD in that car
So lost as to how to fix this

 

Why would you do that? Ground a power wire I mean.
An ammeter wire should never be grounded. Any type of amp meter only has positive power going in one side or the other no ground. Grounding, or shorting, is when you have fires. Not necessarily with a shunted Meter like you have, but I’m trying to make a point about the type of wire you’re talking about grounding.
Anytime you ground a wire with 12 volts on it, the wire will melt, or the fuse will burn (if it has one), or you will harm something else
In other words, never ever ground an ammeter wire!

It’s just a gauge. It’s absolutely possible to run the truck without it. There isn’t a single gauge in your cluster that is required for the truck to run.
Only required for you to know what’s going on.

If you must disconnect the ammeter, and I’ll have to go back and reread this to discover why you need to or why it’s not working, just cover any bare end of a wire to keep it from shorting to ground.

A very viable alternative, at least as a temporary monitor, is a voltmeter stuck into the cigarette lighter.
The digital readout will give you a constant monitor of what’s going on.

 

Was refeering to the article on installing a volt meter where the ground the yellow wire for the installation. Just trying to form a plan go get this thing going again after the MSD power surge killed it. Oh had the alternator tested at Oreillys and it is bad , have not tested the voltage regulator yet have to figure out how

 

Ahh, so disconnected from power, and used as the ground side for the new voltmeter. Ok, I get what you’re saying now.

Good you took the time to test the alternator. Hope your new one lasts a long time.

Not sure how to test a regulator anymore myself. But it probably depends on whether it’s a more modern IC type, or the old point type.
The different service manuals usually spell it out for the original regulator type. Not sure about testing the newer type.
You can always just hook it up and see if it works. Or just replace it now, since most people I’ve ever spoken to have recommended replacing regulators every time you change the alternator.
Personally, I never did. I only waited for them to fail before I changed them. For me, it rarely happened at the same time. And nowadays, with the crappy quality of modern parts, I might be even more inclined to Wait and see.
If I had a properly working old regulator, I’d want to keep it.

 

Did you buy a new alternator already, after your old one tested bad?