One wire alternator

[85lebaront2]

My "souped up" 3G is essentially a Taurus 3.8L 130 amp 3G (which is an easy way to get one) It uses two wires, a big output wire through a 200amp megafuse and a small LG/R from the instrument cluster idiot light. I can get a 130 amp one easily (I actually have a spare) if I need it.

The reason I am not a huge fan of one wire units, if your gauge, be it the original "I might actually read" unit or a converted to a volt meter one, unless you watch it on starting and keep an eye on it driving, you may not realize the alternator isn't charging. The idiot light gives a real fast "it's charging" on start up and a pretty quick "oh crap" if it quits.

[Gsmblue]

Wow, so much info!!!

I am not sure i will keep this 1 wire. It is amazon so returns are easy.

[Gary Lewis]

If you go with a 3G THEN you can clean up the old wiring.  Remove the regulator from the fender.  Get rid of the undersized charge wire, etc.  'Cause wherever you go you can get a replacement.

I don't know about the Powermaster, but a bog stock 3G puts out as much at idle than a 1G does at full tilt.  Your lights will stay bright.  The HVAC fan stays spinning rapidly, etc.

[Gsmblue]

Tonight I pulled out my 1981 EVTM and and started to look at this more closely. The picture below is the actual wiring harness for my 1G alternator.

NOTE: I have only pulled the harness out to make it easy to see what is going on and to fix that S202 splice properly. It will get a nice cover go back in.

My big question is how to disable the shunt in a way that doesn't butcher the harness. It looks like I can just remove it from S202 and tape it up. Is that all I really need to do?

It also looks like power will still get to the voltage regulator, should I leave that disconnected?

Does anyone have any thoughts?

[Gary Lewis]

Depending on what you are going to do you may not need to remove the shunt.  It is just a smaller wire and is capable of handling the full output of the 70A 1G alternators, so if you move the alternator output to the starter relay then the shunt will only be seeing the current into the cab.  And it is very unlikely that you'll pull over 70A in the cab.

As shown on the page at Documentation/Electrical/Ammeter I measured the voltage required to peg 4 different ammeters, and it took from .102 volts to .156 volts depending on the ammeter.  In other words, that's probably the voltage drop across the shunt when carrying 60 - 70 amps.  And that isn't much voltage drop.

But, if you really want to eliminate the shunt just cut it out and put a larger piece of wire in its place between S201 and S202.

[Gsmblue]

Thanks for the feedback. I am going to run a 6 gauge wire to to battery side of the starter relay and I want to change the ammeter for a voltmeter. The rocket an upgrade.

Looks like I don’t need to worry about the shunt but I can replace some of that wiring to the alternator and fix the S202 splice then put one of those nice corrugated covers on and tie it away.

I have read that the external regulators should be disconnected so I will probably remove the regulator from the fender and tape up the connector. The theory being that if I need to buy a 1G alternator I should be able to source a regulator too.

[Gary Lewis]

If you are going with a 1-wire then yes, I'd leave the 1G wiring in place and tape it up.  And it would be wise to buy a new regulator at the same time as the new alternator, so remove the regulator and tape its connector up.

But if you are converting the ammeter to a voltmeter you have one other change to make in the original wiring.  You need to provide both battery voltage and ground to the voltmeter, but only when the key is on or you'll run the battery down powering the voltmeter 24x7.  One way is shown below.  It uses the original wiring that runs to the ammeter, but you remove the yellow/light green wire from S202 and take it to a relay that grounds it when the key is turned on.





Another, probably easier, way to do that is shown below.  Don't mind that it shows a 3G alternator, you can still wire the 1-wire as in the previous schematic with the large wire going to the battery side of the starter relay, although I'd recommend installing a fuse in the circuit.  But if you wire the voltmeter this way you won't have to have the relay in the previous approach.

[Gsmblue]

Gary,

That last diagram has confused me a little bit. I get the grounding of the Y/LG on one side of the Ammeter (to be voltmeter), no problem.

The other +Ve side has me confused the LG/R wire is normally connected to the external voltage regulator then on to the dash cluster. But now it is not connected to anything that I can see. Where is it getting it's +Ve from?

[Gary Lewis]

That LG/R wire is the key-on power to the alternator.  It bootstraps the alternator in.  (There's the difference in a 1-wire and a normal alternator.)

Note that it says "Continued on Page 16".  Here's Page 16:  (NB: This is from the 1986 EVTM as it is showing the 2G firestarter alternator, and the '86 trucks were the only Bullnose trucks afflicted with them.  And, btw, you are one of the few on here that understands "NB".  )

[Gsmblue]

Ah! I thought it was an output from the voltage regulator to the dash, but it is the other way around!

Thanks Gary, as always invaluable help!

I will grab a mega fuse later on today and hopefully I can get this all wired in :)

[Gsmblue]

Had to order the 175amp fuse holder online so I won't be finishing this until next week.

I will update my project thread then and link it to here to make sure it all gets closed out, just in case someone searches for such a topic in the future :)

Thanks for all the help as always!

[Gary Lewis]

[Gsmblue]

The new alternator is in and all wiring squared away. Wife dragged me out to a happy hour but will post pics when i get back!

Thanks for all the help.

[Gary Lewis]

Congrat's!  But, did it work?

[Gsmblue]

Yes!! No more dimming lights!

[Gary Lewis]

[Gsmblue]

Ok, pics:

Starter relay, 175amp fuse and 1/0 wire going ti alternator.

Cleaned old harness and tapped up. Tucked out the way.



Shiny spinny thing

[Gary Lewis]

Well done!  

At first it looked like the red cable on the battery side of the starter solenoid just wrapped around on itself.  But on closer examination I see that it goes to the fuse and there's a short positive cable to the battery.

I'll bet that charges quite well with that heavy cabling.  

[Gsmblue]

Correct. I had to be creative with the wiring routing and fuse placement. Took her for a nice cruise this morning. No light dimming, no subwoofer wobble/farting.

One step closer to summer readiness.