Introducing Myself

[Schwabber]

Bummer! I hope you prevail.

As for the 3G, it doesn't need to be a 302. Even Bill's 460 should work for pics. But, doesn't this drawing on the 3G page do it?

Hi - well so, I scratched my head a lot and finally tabled to effort last year, but back at it again with new vigor. After looking at this diagram again fresh I think I finally have it figured out in my head. I don’t have the ammeter converted yet so thinking to just reconnect everything except the yellow wire for now and leave It for when I get the ammeter converted to a voltmeter. Is there any reason not to do that?

Thanks,

Brian

[Gary Lewis]

Hi - well so, I scratched my head a lot and finally tabled to effort last year, but back at it again with new vigor. After looking at this diagram again fresh I think I finally have it figured out in my head. I don’t have the ammeter converted yet so thinking to just reconnect everything except the yellow wire for now and leave It for when I get the ammeter converted to a voltmeter. Is there any reason not to do that?

Thanks,

Brian

If by "the yellow wire" you mean the yellow white wire, then the alternator won't work if you don't hook that wire up. Or, maybe I should say it'll work w/o regulation and the output voltage will go very high. Don't do that.

But if what you are worried about is the ammeter, then you could do the 3G conversion and leave the ammeter. It is a bit risky as the shunt may melt if the alternator is required to recharge a dead or very low battery. But if you are careful and charge the battery up before starting the truck the first time you should be ok.

[Schwabber]

If by "the yellow wire" you mean the yellow white wire, then the alternator won't work if you don't hook that wire up. Or, maybe I should say it'll work w/o regulation and the output voltage will go very high. Don't do that.

But if what you are worried about is the ammeter, then you could do the 3G conversion and leave the ammeter. It is a bit risky as the shunt may melt if the alternator is required to recharge a dead or very low battery. But if you are careful and charge the battery up before starting the truck the first time you should be ok.

That make sense about the yellow/white wire coming from the regulator. But there is a 10 gauge all yellow wire that is spliced onto the charge wire and into a connector together with the ignition wire coming from the reg. I was figuring that was the shunt and only used to detect charge condition and had nothing to do with regulation

[Gary Lewis]

That make sense about the yellow/white wire coming from the regulator. But there is a 10 gauge all yellow wire that is spliced onto the charge wire and into a connector together with the ignition wire coming from the reg. I was figuring that was the shunt and only used to detect charge condition and had nothing to do with regulation

The wiring is shown below, which is out of the 1985 EVTM here: http://www.garysgaragemahal.com/charge--power-distribution-gas.html on Page 17. And if the wire circled in red is the one you mean it won't work leaving it off. If you turn to Page 18 in the EVTM, shown further below, you'll see where that yellow wire goes - to the ignition switch. It feeds a lot of things, including the ignition.

The shunt is the black/orange wire, marked Shunt in the first diagram, and it is what isn't up to handling the full output of the 3G alternator. It is probably rated at a max of 70 amps as the largest alternator available on these trucks was a 70a unit. So you might get by leaving the shunt in if you never run the battery down very low, which would require the alternator to go to max output.

Or you can wire around the shunt. Run a #10 wire between the two connections circled in maroon and that will bypass the shunt as well as the ammeter. Good to go.

[Schwabber]

The wiring is shown below, which is out of the 1985 EVTM here: http://www.garysgaragemahal.com/charge--power-distribution-gas.html on Page 17. And if the wire circled in red is the one you mean it won't work leaving it off. If you turn to Page 18 in the EVTM, shown further below, you'll see where that yellow wire goes - to the ignition switch. It feeds a lot of things, including the ignition.

The shunt is the black/orange wire, marked Shunt in the first diagram, and it is what isn't up to handling the full output of the 3G alternator. It is probably rated at a max of 70 amps as the largest alternator available on these trucks was a 70a unit. So you might get by leaving the shunt in if you never run the battery down very low, which would require the alternator to go to max output.

Or you can wire around the shunt. Run a #10 wire between the two connections circled in maroon and that will bypass the shunt as well as the ammeter. Good to go.

Gary - I have noted 2 different configurations for how to wire the A yellow wire coming from the regulator. In your schematic, it shows it going straight to the battery side terminal of the solenoid, bypassing the fuse. In the schematic that came with the alternator/harness, it shows that wire going to the B terminal of the alternator and thru the fuse. Is there is case for bypassing the fuse that would justify undoing how the harness came from the supplier and splicing it connect it at the solenoid as depicted in the physical depiction your provided previously. Also, I am still not certain what to do about the ammeter. In your last note, you said to run a 10 wire splice between the 2 maroon circles on the schematic in order to bypass the shunt, , but that looks like the same thing as the shunt to me?

Thanks,

Brian

[Schwabber]

Gary - I have noted 2 different configurations for how to wire the A yellow wire coming from the regulator. In your schematic, it shows it going straight to the battery side terminal of the solenoid, bypassing the fuse. In the schematic that came with the alternator/harness, it shows that wire going to the B terminal of the alternator and thru the fuse. Is there is case for bypassing the fuse that would justify undoing how the harness came from the supplier and splicing it connect it at the solenoid as depicted in the physical depiction your provided previously. Also, I am still not certain what to do about the ammeter. In your last note, you said to run a 10 wire splice between the 2 maroon circles on the schematic in order to bypass the shunt, , but that looks like the same thing as the shunt to me?

Thanks,

Brian

Forgot to attach pic of the competing diagrams

[Gary Lewis]

Gary - I have noted 2 different configurations for how to wire the A yellow wire coming from the regulator. In your schematic, it shows it going straight to the battery side terminal of the solenoid, bypassing the fuse. In the schematic that came with the alternator/harness, it shows that wire going to the B terminal of the alternator and thru the fuse. Is there is case for bypassing the fuse that would justify undoing how the harness came from the supplier and splicing it connect it at the solenoid as depicted in the physical depiction your provided previously. Also, I am still not certain what to do about the ammeter. In your last note, you said to run a 10 wire splice between the 2 maroon circles on the schematic in order to bypass the shunt, , but that looks like the same thing as the shunt to me?

Thanks,

Brian

Brian - The part you've missed is that the diagrams above are for the original alternator, not the 3G. I only showed them to discuss the shunt. And while I'm on that subject, yes you do need to run a 10 gauge wire between those two maroon circles. The 10 gauge wire is much larger than the shunt and will have essentially no voltage drop across it so the ammeter won't burn out, nor will the shunt.

As for the diagram, you are supposed to use the one on the 3G page, shown below for convenience. It is essentially the same as the top diagram in your link. But those are for a truck with a warning light. Unfortunately I don't have one for a truck with an ammeter on the site. And I can't see enough of the lower diagram in your link to know where it is getting its power going to the "I" terminal on the alternator.

So, can you get a better pic of that diagram and include the part in the lower right corner?

[Schwabber]

Brian - The part you've missed is that the diagrams above are for the original alternator, not the 3G. I only showed them to discuss the shunt. And while I'm on that subject, yes you do need to run a 10 gauge wire between those two maroon circles. The 10 gauge wire is much larger than the shunt and will have essentially no voltage drop across it so the ammeter won't burn out, nor will the shunt.

As for the diagram, you are supposed to use the one on the 3G page, shown below for convenience. It is essentially the same as the top diagram in your link. But those are for a truck with a warning light. Unfortunately I don't have one for a truck with an ammeter on the site. And I can't see enough of the lower diagram in your link to know where it is getting its power going to the "I" terminal on the alternator.

So, can you get a better pic of that diagram and include the part in the lower right corner?

Gary, it occurs to me that another possible source of confusion here is that I have not fully described how I am going about my solution. I am not using the existing original harness at all - the one on the truck was fried and I could not find a donor vehicle. So, I am using a 4 ga charging wire going direct from the Alt B terminal to the 175 a fuse to the battery side of the solenoid. From my understanding of prior discussion, it seems to me that this should prevent frying the shunt, but at the same time the ammeter will be always showing a draw condition even if/when the alternator is charging. If this is correct, then I think I am ok with that. I do plan to convert the ammeter to a voltmeter as discussed elsewhere, but it sounds to me as though that change is not a precondition to getting the alternator installed and the truck running again.

The other question unresolved with this approach, is what to do with the yellow charge wire discussed previously. I gather that I will need to connect a 12 ga wire to the battery side of the solenoid on top of the 4 ga wire coming from the alt, and splice that into the existing 12 ga yellow wire that goes into the connector and off to the dash with the ignition wire.

I've attached the full diagram from the provider of the harness, and a photo of the connector described above

Thanks for sticking with me on this. I imagine this must me a real pain for you too. ;)

 

[ArdWrknTrk]

I have noted 2 different configurations for how to wire the A yellow wire coming from the regulator. In your schematic, it shows it going straight to the battery side terminal of the solenoid, bypassing the fuse. In the schematic that came with the alternator/harness, it shows that wire going to the B terminal of the alternator and thru the fuse.

In your last note, you said to run a 10 wire splice between the 2 maroon circles on the schematic in order to bypass the shunt, , but that looks like the same thing as the shunt to me?

Maybe I can help?

The 'A' wire is 'alternator' and senses system voltage at the alternator.

It could be at the actual output post, or the alternator side of the 175A fuse.

If for some reason that fuse were to blow, break or corrode the alternator would go 'full field' and meltdown in just a few minutes.

This is why it should be attached before the fuse.

The existing B/O wire between the two circles is deliberately undersized for the 60?A alternator you have.

This forces some current to flow through the a meter, and this is what the meter reads.

The 3G can put out twice as much amperage, and the existing shunt is far too small to handle that.

If you had a high current draw it would try to find the path of least resistance, and as the shunt heated up more current would try and find its way through the meter, probably melting it or (in an extreme case) causing a fire.

So you replace the shunt with a 10Ga. wire that can handle all the cab loads.

 

[Gary Lewis]

I have noted 2 different configurations for how to wire the A yellow wire coming from the regulator. In your schematic, it shows it going straight to the battery side terminal of the solenoid, bypassing the fuse. In the schematic that came with the alternator/harness, it shows that wire going to the B terminal of the alternator and thru the fuse.

In your last note, you said to run a 10 wire splice between the 2 maroon circles on the schematic in order to bypass the shunt, , but that looks like the same thing as the shunt to me?

Maybe I can help?

The 'A' wire is 'alternator' and senses system voltage at the alternator.

It could be at the actual output post, or the alternator side of the 175A fuse.

If for some reason that fuse were to blow, break or corrode the alternator would go 'full field' and meltdown in just a few minutes.

This is why it should be attached before the fuse.

The existing B/O wire between the two circles is deliberately undersized for the 60?A alternator you have.

This forces some current to flow through the a meter, and this is what the meter reads.

The 3G can put out twice as much amperage, and the existing shunt is far too small to handle that.

If you had a high current draw it would try to find the path of least resistance, and as the shunt heated up more current would try and find its way through the meter, probably melting it or (in an extreme case) causing a fire.

So you replace the shunt with a 10Ga. wire that can handle all the cab loads.

Thanks, Jim!