OK, here goes...

I got this 200 amp rebuilt alternator with my short bus.



It's a lot like my old one...circumference is 18 1/2" to my current one at 17" and it doesn't quite fit right in the bracket. That is nothing that two (2) flat washers on each bolt won't fix as spacers.

The pulley is 1/2" smaller in diameter, width and groove count is the same, no problem there.



The alternator off of the short bus has a different plug and it uses that center pin with a jumper over to another plug on the alternator.



Here is a shot of that other plug on the back of the 'new' alternator, it just goes to the main plug center pin so no change needed there.



Here are the plugs.





My snag is with the two wires that come out of the plug and into the harness. I will attach bullet connectors and heat shrink them, that way I can reinstall the old alternator if necessary (I'll probably rebuild it and keep it in stock).

The two wires in the truck are same color scheme, green wire w/red stripe, identical, no difference in width of stripe or anything.

The plug that came with the short bus has two different colored wires, one red, one green IIRC. Any help on how to make that connection? Or does it not matter?

Thanks,
Mark

 

OK, I called the company on the label at their toll free number and they set me straight. They are in Baltimore and they build up alternators mostly for municipalities in the Baltimore, DC, Northern VA area.

The man seemed pretty knowledgeable and was very helpful and cooperative. He said that I just needed to keep right wire to right wire, left wire to left wire with the changeover. He said that if I got them mixed up it could cause no harm but the battery light on the dash would not light at KOEO.

I went ahead and added bullet connectors in a manner that they cannot be hooked up wrong (one male and one female each on the harness and the alternator connector). Two flat washers 'round the house for shims, belt back on and fired it up. Battery light lit at KOEO. Batteries tested at 12V before starting and 11 after starting. WTH. Turned on A/C, full fan and headlights and watched the voltage gauge dip...then recover. Tested to 13.6V at idle w/AC, full fan and headlights. Got a stick for the fuel pedal and up to 14.3V at 1500 RPM. Off with the lights and A/C and holding 13.2+- at idle, more than the old alternator did. Shut it off after a few minutes and 12.3V at the batteries. I'll keep my meter in the truck and monitor them and see what they level off at.

 

WH, get one of these and you can watch it all the time

Equus Innova 3721 Battery and Charging System Monitor - Walmart.com

If you have Amazon Prime

 

OOPS! On edit... sorry! Check out your tail lights. You're way ahead of me. I started typing this post, but got called away to work, and by the time I came back, the thread was updated. I'm posting anyway, since I spent all the time typing it, and it could be of help to someone else searching to do the same thing (6G to 3G conversion)





What do you mean by "short bus". You often refer to it. Do you have one of these?










This is a 3G alternator. AKA Ford's "3rd Generation". You are replacing a 6G (6th Generation) alternator by stepping back to a third generation. This isn't a problem, it has been done before. Use what ya got! The alternator in the photo above is obviously a rebuild. The large number is the Lester trade number that you can back trace to all the Ford vehicles that came with this alternator.

Quote:

Originally Posted by Walleye Hunter

It's a lot like my old one...circumference is 18 1/2" to my current one at 17" and it doesn't quite fit right in the bracket. That is nothing that two (2) flat washers on each bolt won't fix as spacers.

Then that is an easier size upgrade than moving to the large case 6G alternator, which requires a touch of grinding at the bottom valley of the alternator bracket. Recognize that you may need slightly longer bolts to maintain the same amount of friction on the bolt threads. The more thread engagement, the better chance those bolts will stay tight as the engine is jiggling and the drive belt is yanking the alternator around on it's mount. Your bolts may be long enough as is, but if there is any doubt, change them out.


Something else to think about... the radiator hose clearance. If you already upgraded your top radiator hose to the dual alternator type that goes around the drive belt rather than through it, then you might have a CLEARANCE ISSUE between that hose and the larger 3G alternator case, when the hose expands from heat.


The top dual alternator hose is routed very close to the bottom hemisphere of the top alternator. A larger diameter alternator makes the two even closer. Add heat and movement, and you can see this is something to pay attention to during the install.







So what are you going to do about the belt, or the pulley? There may not be enough range in the tensioner to absorb the 13mm difference you report. If you change the pulley to the stock size, you will reduce the alternator RPM to engine ratio, and produce less than the rated amps on the alternator. If you change the belt... then keep good notes in the glove box on what "alternative" (ha ha) belt you are using, so it can be readily replaced on the road.

Quote:

Originally Posted by Walleye Hunter

The alternator off of the short bus has a different plug and it uses that center pin with a jumper over to another plug on the alternator.

That center pin on the three wire alternator plug (hereinafter referred to as the D shell connector, because the outermost shell is shaped like a D), and the separate single pin square connector, are for the stator circuit. The stator circuit on the 6G alternator is internal, but not so on the older 3G alternator. The 6G alternator still has the same circuit, it just isn't visible externally. So you will need to maintain the external stator wire (White/Black) between the D shell connector and the square single pin stator connector.

Quote:

Originally Posted by Walleye Hunter

Here are the plugs.

I don't understand your sentence about your snag. You said your "snag is with the two wires that come out of the plug and into the harness".


Out of what plug?
Into which harness?


Do have the cut off harness pigtail scavenged from the short bus you extracted the 3G alternator from?


Or are you referring only to the harness pigtail that is currently part of the wiring to your early 99 truck into which you are installing the alternator?


If you have the scavenged cut off wiring harness that already has the center stator pin to stator wire square plug, and the D shell plug that plugs straight into the D shell connector on the 3G alternator, then that's one thing.


If you don't have any cut of wiring pigtails at all, and you are just dealing with a bare 3G alternator, and your incompatible Early 99 truck wiring harness still attached to your truck, that's another thing.


I'd suggest different solutions, depending on which thing you have, but I think it still might be easier if you get a translation harness that will solve all your issues, including your desire to be able to quickly go back to a 6G style alternator should your rebuilt 3G fail down the road. More on my proposed solution in a little bit, at the end of this post.


But first, I want to address this:

Quote:

Originally Posted by Walleye Hunter

The two wires in the truck are same color scheme, green wire w/red stripe, identical, no difference in width of stripe or anything.

That ain't right. Only ONE wire on your truck should be Light Green with a Red stripe. That wire is your Ignition circuit, or "I" circuit, Ford circuit #904. When the ignition switch is turned to Run, voltage is applied (first through the alternator warning light on the dash) to the voltage regulator in the alternator. This turns the voltage regulator ON.


The other wire should be Orange with a Light Blue stripe. This is the "A" circuit, also known as the "Sense" or "Battery Sense" circuit, and sometimes interchangeably referred to as the "AS" circuit. Whatever. Ford calls it "A", and the circuit number is #35. When the voltage regulator got turned on by the I circuit in the paragraph above, current got permission to flow from the battery sense circuit to the field coil.


Once the engine is started and the rotor starts spinning, AC current is generated and converted to DC current that is output to the big B+ terminal that the larger black and orange wire attaches to. As the current is being generated, a reduced voltage signal is taken from the stator and fed back to the regulator, in your case, via that white and black wire that goes to the middle of your 3 pin D shell connector.

Quote:

Originally Posted by Walleye Hunter

The plug that came with the short bus has two different colored wires, one red, one green IIRC. Any help on how to make that connection? Or does it not matter?

Heck yes it matters. See paragraphs above.


The only case where it wouldn't matter is if you were to make your own translation harness, and then the color of the wires you choose to make the translation harness wouldn't matter, so long as you knew which wire went where between the truck harness and your alternator plug.


But you've got a problem if both wires on your truck harness are colored the same. They shouldn't be. The circuits go different places, both on your truck, as well as inside your alternator. You'll have to try cleaning the wires and using a magnifying glass... or do what I do sometimes... get someone 40 years younger to tell you what color things are, just to verify.


Once you get your truck wire harness sorted, as to which wire is the Ignition I circuit 904 vs the Battery Sense A circuit 35, then I recommend you get the following translation harness, for a cleaner install that is more easily removed should you need to go back to a 6G alternator of either the original small case or the alternative large case variety.


And here it is...





And here is where to get it...


http://www.ebay.com/itm/Alternator-Conversion-Harness-Connector-Lead-Adapter-Ford-6G-TO-3G-w-Stator-lead-/200976771001?hash=item2ecb2627b9&vxp=mtr

No affiliation... just some random eBay seller. There are likely other places to get this ready made translation harness. It was just the first hit in my search on your behalf.

 

Nice write up Y2KW57. Tried to rep you for the work but says I gotta spread the love

 

Whew, that's a lot to address Y2KW57

Yes, I got short bus out of DC, it looked like this.



I kept the pigtail off of it and already spliced it in with bullet connectors to permit me to switch the original alternator back in if needed. I'll keep the original pigtail in the alternator so I don't lose it. Shimmed it with washers so it would fit in bracket and I expect that the shim job should pretty much cover difference in size on the pulley, it works fine with original belt.

I am sort of surprised that it is an older style alternator as it was in that '03 short bus and the pigtail had not been modified.

Thanks for all that input.

OH, and both wires are same color in my truck and it all looks original.

 

my guess is that who ever was supplying engines for the bus builder or the bus builder themselves hadn't upgraded to newer ones like Ford. Probably not a lot of electrical load on a school bus

 

The bus builder buys the chassis from Ford with the engine and tranny in it and mounts the bus body on it. The only things that would add load to the alternator should be the flashing lights and the additional HVAC equipment. It had a remote condensor with two fans midway back the left side and an evaporator and blower up top in the rear.

 

Built at a different plant to different specs maybe?? Still had a bunch of 3G Alts and they worked for the bus requirements? just guessing

 

Here's how the truck came from Ford.
VIN Decoder - Ford Truck Enthusiasts Forums
And the alternator fit in the bracket on the bus without modifications.

 

Nice work!