Not Understanding My Wiring

[Lewis]

Hello all. First post here.

I�m not understanding some wiring on my �51 CJ3A. It�s 12V, and has an alternator. It had a foot starter with the manual metal lever. I put a high torque starter and 4 pole switch from KW on it, and I�m using the attatched diagram to help me. But the alternator has one wire coming off the starboard DA plug spade to the coil, one to the ammeter and a ground.

I�ve seen some push button start setups online for old cars that show a wire from the port spade of the DA plug to the coil. I haven�t seen an example of the alternator being grounded.

Do you think I should just wire it up like the diagram, with no wire from the alternator to the coil? In this case, do I need a jumper from the DA to the post on the alternator, like in the attached stock photo (it shows an arrangement for a push button start, but I�m using a 4 pole switch).

I�m also attaching a couple pics of my mess. I ordered a new wiring harness from KW, but I�m not sure what setup it includes.

One last thing - I have the ammeter hanging out of the dash and would like to play around with it while I wait for the wiring harness. Does the ammeter mount ground it or anything or is it safe to use while just hanging out if the dash?

Thank you in advance for any advice.

[squidtone]

Your first diagram shows, I believe, the "one wire" alternator. It appears that you have the classic "3 wire" Delco 10SI, but check the numbers to be sure you actually have a alternator with an internal regulator.
So, you can't wire your alternator according to your first diagram. The 3 wire alternator is arguably superior anyway, and if wired correctly, works great. Hooking up a 3 wire alternator can be confusing because you can choose different points to connect to and it's a matter of personal choice.
The simplest way to wire a 3 wire alternator is to loop a short wire from the #2 terminal right to the battery output post as shown in the Vintage Garage image you posted. However, it is considered better if you can connect terminal #2 of the alternator closer to where all your accessories and components draw power. In your case, it's probably on the "load" side of the ammeter. Original Jeeps served out most of the power for the gauges and lights from that load side of the ammeter.
The #1 terminal of the alternator needs to be wired to the "ON" terminal of your ignition switch. This basically turns the alternator "ON" and allows it to charge. More importantly, it removes battery power to the alternator (turns it "off") when you turn the Jeep off, and prevents the battery from getting run down.
The "BAT" terminal of the alternator could be run with a 10 gauge wire to the "BAT" side of your ammeter. Some folks don't like passing another 10 gauge power wire through the firewall, so you could simply run it directly to your positive battery cable clamp. (You might want to get a new positive battery cable with an extra lead for this purpose).
I'd be nervous having my ammeter hanging out of the dash. That's a BIG short just waiting to happen if you hit a bump, or your foot. Instant melted cable, smoke, fire.
By the way, sometimes folks who've switched to 12V just get rid of the ammeter and put in a Voltmeter instead. Something to think about.
If you ordered a stock harness, you won't get a fuse panel, or a ballast resistor setup; a few nit picky things about a 12V conversion that you should make sure you get right. Check out your coil to see if it's external or internal resistor.
But anyway, you can modify a stock harness to make it work for you without much trouble at all.

Good luck!
Dave

[athawk11]

I don't know much about alternator wiring, (I'm a generator guy) but I do want to emphasize that you don't want the ammeter or ammeter wiring to ground out in any way on the tub.

[Lewis]

Thank you very much for the replies.

A couple more questions:

1. Will the ammeter indicate correctly if I run the BAT wire directly to the battery?

2. Any idea why it doesn�t have a ballast resistor now? Is it required because of the key start or did whoever converted it to 12V not do it correctly?

3.� So there will longer be a wire straight from the alternator to the coil? Only one from the alternator to the key, and one from the key to the coil?


Again, thank you very much!

[stony]

No, an ammeter reads current, and a voltmeter reads voltage.  An ammeter is wired in SERIES and a voltmeter is wired in PARALLEL the circuit.  The ammeter reads the current  from the generator (alternator) flowing into the battery.  A voltmeter reads the voltage of the battery.  So for a ammeter to work it must be in the line.

[stony]

For example when you start your Jeep in the morning you put a huge drain on the battery, sucking out amps, and dropping the voltage.  Your generator needs to recharge the battery.  With an ammeter you will see an increase in the current flowing to the battery.  You may see +20 amps which will gradually decrease to 3 or 4 once the battery is full again.  With a voltmeter you will see a drop in voltage, maybe down to 11 or 12, then gradually come up to about 14 when you are fully charged and your generator is working.

[specialty]

I used this page when I rewired my 3A with a 3 wire alternator.
http://www.how-to-build-hotrods.com/hot-rod-wiring.html
It's simple and easy to understand. give it a look, has various wiring topics including using relays fr headlights, horn, signals and everything you will need.

[squidtone]

Hey Lewis,

Here's my comment on your questions from your followup post:

1. Will the ammeter indicate correctly if I run the BAT wire directly to the battery?

Yes, that's fundamentally how it should be set up. However, it can get confusing because you could also wire it directly to the "always hot" side of the ford style solenoid, and some folks might even wire to the alternator post. I'd wire your ammeter "BAT" either directly to the postitive terminal of the battery, or to your Ford style solenoid if you have that. By the way, the wire going to your "BAT" side of the ammeter should probably be 8 or 10 gauge.

2. Any idea why it doesn�t have a ballast resistor now? Is it required because of the key start or did whoever converted it to 12V not do it correctly?

Your coil might be of the type that has a built in resistor so you would not need an external ballast resistor. You should check your set up because depending on what you have and how it's set up, you may suffer from reduced point life in the distributor.
If you find a regular coil that says "requires external resistor", you should then install a ballast resistor. A side benefit of running a regular coil with an external ballast resistor is you can get a hot spark during starting from many types of starter solenoids; it's all automatic and easy to rig up. Most cars from the 60's and 70's used this hot spark method.

3.  So there will longer be a wire straight from the alternator to the coil? Only one from the alternator to the key, and one from the key to the coil?

Right, but with more details: As shown in your engine bay picture, #2 terminal of the alternator wire is going to the + terminal of the coil, and #1 terminal is broken. I suppose it's possible it worked, but I submit it was wrong. Instead, do this: Run #2 terminal of the alternator to the "BAT" post of the alternator, or better yet to your "LOAD" side of your ammeter (small gauge wire like 14-16 awg is fine for this).  Run #1 of the alternator all the way to your "ON" of the ignition switch but please note: you should put an "idiot" light in series with this wire. A radio shack weenie 12V indicator bulb will be fine. Some folks use a small resistor in series instead (not sure what resistance). This bulb if mounted in the dash is a great indicator that you're actually charging, and it also prevents other squirelly things from happening like backfeeding the ignition, etc.

[specialty]

I got the little red bulb from Advance Auto designed for about a 3/8 dash hole which I had beside the speedometer for the charge indicator light. I think the hole was originally for the gauge lights, external. Like you said, it lets you know when it's charging. Turn on the key, it's red so you know you have power. Start engine, if charging, goes off. Nice set up.

[Lewis]

Thanks for the replies. Here�s a picture of what I came up with. Any comments are appreciated.

[squidtone]

Hi Lewis,
Nice diagram. I would swap the horn and headlight power side for side. The ammeter is not big enough for the huge current that horns use. The original wiring had the horn power lead directly from the battery side of the ammeter so the ammeter needle would not have to get "pegged" when using the horn. The headlight power should be fine on the "load" side of the ammeter and the needle of the ammeter should handle that power fine.
I see you have a ballast resistor in there....I'm assuming you've got a plain 12V coil that needs it. So it looks good!
Good luck.
Dave

[aboyandhisdog]

Hi Lewis,
Nice diagram. I would swap the horn and headlight power side for side. The ammeter is not big enough for the huge current that horns use. The original wiring had the horn power lead directly from the battery side of the ammeter so the ammeter needle would not have to get "pegged" when using the horn. The headlight power should be fine on the "load" side of the ammeter and the needle of the ammeter should handle that power fine.
I see you have a ballast resistor in there....I'm assuming you've got a plain 12V coil that needs it. So it looks good!
Good luck.
Dave

Great info here!  I'd just restate that if your coil has an internal resistor, you don't need the external one on the firewall.  As for the horn, I just got power directly from the battery - it just seemed simple at the time. 8-)

[Lewis]

Thanks a lot, guys.

I�m not sure about my coil yet. It only says �12V� on it. I�m trying to figure out how to test it. There�s not external resistor right now, but who knows if it�s correct.

Thanks again!

[specialty]

I would do away with the external ballast. Just get a coil with internal resistor and eliminate that problem. A early 70's model chevrolet coil will have a internal resistor and cost about $20 and works great with a 3 wire alternator.

[aboyandhisdog]

More $ but this coil has worked great in my 3a: 

https://smile.amazon.com/PerTronix-40611-Flame-Thrower-Volt-Coil/dp/B000N2XOYE/ref=sr_1_1?ie=UTF8&qid=1535249473&sr=8-1&keywords=pertronix+40511+flame-thrower+40%2C000+volt+3.0+ohm+coil