Motorola Alternator - what is the yellow wire for???

[Elizabeth_B29]

Hello Afourians!

I have uploaded images of the alternator I am going to install on my A4.
Had it checked at an alternator shop. Tested good but the yellow wire befudled the "testor". What is it for? Tach? the alternator shop told me that if power was applied to the yellow wire that the output voltage quickly increased to 18 volts.....wuuuuut????

This alternator is off my spare A4 from a Pearson Triton. The altenator shop told me to attach the brown wire with the plastic terminal to the ignition and to connect the larger post to the battery bank. I plan to attach the positive out from the alternator to the + on the starter solenoid and use 10 gauge tinned wire with crimp on heatshrink terminals.
I plan to connect the brown "ignition" wire to the ballast resistor that goes to the distributor, to the "in " terminal or the upstream terminal on the ballast
Whaddya' think? - ELizabeth

[Elizabeth_B29]

annnd the image

mea culpa for some reason the image didn't make, I will try if again.
Cheers! Elizabeth

[hanleyclifford]

In your picture they are showing a label "AC tap" in the direction of the yellow wire. If it really is an "ac tap" aka stator terminal it is for a tachometer for diesels or certain types of external voltage regulators. I think you may need to just cover that wire and see how the alternator does without it connected to anything.

[ndutton]

In your picture they are showing a label "AC tap" in the direction of the yellow wire. If it really is an "ac tap" aka stator terminal it is for a tachometer for diesels . . . . .

And mine! I have such a tap connected to an alternator driven (diesel type) tachometer. The alternator shop that added the wire for me made it yellow as well.

BTW, it works great but be advised if considering the addition of such a tachometer it will have to be calibrated after installation. Easy to do with a Harbor Freight optical tach tool.

[joe_db]

I would take the regulator off and see what that goes to. My guess is it connects to the field to provide for a way to boost the charging rate. It would behave like you saw - putting power on it increases voltage. The AC tap is where the arrow points - not under the reg.

[ndutton]

One more thought

If the wire befuddled the alternator shop it's time for a new alternator shop, one with marine experience. We have two distinct and equally possible theories what it might be right here on this forum and none of us claim to be alternator professionals.

If they're thrown a curve by the yellow wire, where are they with SAE J1171 Ignition Proof standard? That's a critical feature for us. Nope, there's a bigger problem here than a yellow wire.

[joe_db]

Good point - my local alternator shop would have figured it out in about 10 seconds or less.

btw - not sure if this counts as being a pro, but I used to be a dealer for Balmar

[ndutton]

btw - not sure if this counts as being a pro, but I used to be a dealer for Balmar

It counted when you hung your shingle out and charged money for alternator services (the definition of professional) but assuming those days have passed you're now a rank amateur like the rest of us schmo's.

Although your rank as an amateur is one with considerable experience. Perhaps a higher rank?

[hanleyclifford]

It shouldn't be hard to tell if the yellow wire is from the stator (AC); just see what it reads with the engine running; should be about half the output.

[Elizabeth_B29]

Motorola alternator yellow wire

Thanks All!
I think joe_db has it figured out...
The yellow wire comes from the regulator, the AC tap is a post covered with a clear plastic cap...see photo.
I am going to install the alternator along with an electronic ign. converted prestolite distributer with a 1 ohm ballast resistor and new coil. My engine came with the same distributer but it is quite rusty inside the flyweight/ spring area. I have a second engine that I purchased as a spare that had most of the Moyer bells and whistles so I have a spare distrib. that looks essentially new.

The existing alt on the engine has an external regulator, the PO showed me that he ran the engine with the alternator unregulated, with a terminal that connected to the alternator unplugged. It does not seem to make a difference in charging system voltage whether the regulator is plugged in or not, think the external reg is NFG. So I think this gave a full output from the alternator to my new battery bank. Pretty sure I heat/fried my coil with the charging system voltage being too high Last trip out I motored 8 hrs there and back ...no wind..and think this overheated and killed my coil.

I have pulled all the parts from a known working SAE J1171 ignition system and I am going to install all tomorrow, they all look new and tested good. This will give me an internally regulated alternator. The only difference is probably my battery bank.
I have two 6 volt golf cart batteries (series??) for my 12 volt bank. Two details I should have noted on the boat this donor engine came from was
1 - did it have a Tach and 2- what was the battery bank size.

More later and wish me smooth sailing in the installation with as few explitives possible.

Cheers! Elizabeth

[hanleyclifford]

I hope you don't plan to keep running an unregulated alternator.

[marthur]

(series??)

Yes. Two 6 volts in series will give you 12 volts. In parallel they act like a big 6 volt battery.

[Elizabeth_B29]

Yes they are is series (12VDC) and the new alternator is internally regulated.
Just not sure what the system voltage will be until I install the new reg.

Cheers!
Elizabeth

[Elizabeth_B29]

Alternator extra regulator yellow wire identified

Hello Afourians!
I did my homework, opened up the regulator took a look and found the "extra yellow wire" soldered to the terminal that attaches to the brush holder. Hmmmm. The"normal" lead from the alternator that goes to "Ignition" exits alongside this extra wire when the reg cover is closed.

Found a greasy altenator shop in another town piled high with starters and alternators and a guru, a tad greasy too to verify what was inside.
Attached is an image of the inside of the reg.

This extra wire can be used to boost the alternator output or in an emergency to manually regulate the alternator should the regulator fail. I once had an Automac by Spa Creek a few boats in the past and had a setup where I could regulate the alternator output manually. I suspect that this is what the extra yellow was used for on this alternator. I don't know this alt's history so that is the best I can figure. Cheers! Elizabeth

[joe_db]

My "extra" wire is the only wire. I no longer have the regulator connected to the field. This wire runs to an external regulator shown in the photo. The regulator is still in place for ignition protection.