AC CA Wiring

Hello. I am rewiring a 12v system with a one wire 10Si alternator with the 1 and 2 pin posts. I am trying to determine what gauge wire to use from the number 1 pin post back to the voltmeter. I am also curious what gauge wire to run from the coil back to on/off switch. I bought a new voltmeter from TS that has a small light in it. The leads from the light run down to two +/- post on the voltmeter that are separate from the main post. I have not seen this on a voltmeter before. Would this take place of having to put a LED indicator light in line? Any guidance would be appreciated. Thanks.
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The charge wire should be a #10 gauge wire. The ignition wire can be 14 or 12 gauge.
 

With a true one wire alternator you do not use the 1 and 2 posts. Most would have a rubber cap on the 2 posts.

With a 3 wire, the #2 can loop down to the output and #1 goes back to the on/off switch, same post as coil connects back to. This needs a diode, lamp, or resistor to prevent the engine from continuing to run when engine is turned off.

On both alternators the output runs back to battery connection at the starter switch. It would go through an ammeter if you have one.

Are you sure you have a volt meter and not an ammeter. Volt meter would have 0 or low number at left and higher number at right. Ammeter would have 0 in the center.

Ammeter wires in line between output of alternator and battery cable at starter switch.

Volt meter, with negative ground alternator, would wire to frame ground and output connection at the switch (same as wire going to coil). It has no connection to alternator.

I would use 10 gauge wire from alternator output to connection at starter. #16 or #14 for other wires.

Normally a volt meter light in a negative ground system would have post connection to ground and + connection to the output of ignition switch.

12 volt alternator will need a true 12 volt coil (no external resistor required) or a 6 volt coil with extra resistor between coil input and switch.
 
I am editing my post because I think that a huge issue may have been missed in your picture. I am wondering if you have energized the system with it connected as shown? How close did you read the volt meter instructions? Are some type of INSULATED GROMMETS in that part that clamps the voltmeter in the dash? If not I believe the two smaller terminals you have the red and white wires on are the connections for the volt meter and the wires you have on the voltmeter mounting studs are DIRECTLY SHORTED TO GROUND. Now here is where my first reply started.. Here is a link to info on this site for doing 12 Delco 10si I conversion, it has a wiring diagram that also gives wire sizes. If you have no ammeter then those wires would connect together or just are solid wires. Since you claim to have a one wire alternator you will disregard the wires shown to the 1 and 2 terminals of the alternator. Then where it shows the light in the circuit to feed the wiring at number 1 that is where you can hook your voltmeter positive lead and the other voltmeter wire would go to ground. This is due to the fact that if the voltmeter is constantly powered it will run down your battery. If you find you have mistakenly called your 3 wire alt a one wire the voltmeter can still connect the same place just make sure it is on the switch side of the lamp. My apologies to Virgil, this is in no way trying to override what he has diligently typed out and all seems to be very correct. It is just I think sometimes words can be confusing to follow and the diagram should help make it clear.
Wiring diagram


This post was edited by used red MN on 05/06/2022 at 02:49 pm.
 
So maybe I do have a three wire alternator. It has the 1 and 2 post under a cap. They were not previously used when I got the tractor. That setup never charged the battery. I pulled the hole insulators out of the old ammeter that was in there and used them in the voltmeter so I believe they should not be each shorting each other or grounded out. There was nothing other than the voltmeter in the package, so no instructions. I do not recommend this brand, but went ahead with it. Yes, the wiring is not complete on the back of the voltmeter yet as I was trying to figure out what size wires to use to complete the job. I was trying to show the extra wires to the light in the picture. Still confused on the light in the voltmeter as to whether or not it takes the place of an indicator light. I will read through the information in the link you sent. First glance it looks like exactly what I need. Thank you very much for your response. Have a nice weekend.
 
Hook a pigtail to the one marked #1 and fire it up. then touch it to the charge stud on the alternator. If it starts to charge then you have a 3 wire and the #1 wire is the excite wire and the #2 is the sense wire
 
After looking at this today I decided to edit it to take out the wording that described steps that verified how I ..thought.. the voltmeter should be wired in. Now that I have found what looks like it is a similar gauge online that has a wiring diagram for it none of that is needed and would only add confusion. As a check if you feed 12 volts by temporary jumper wires to the two small terminals you have the red and white wires that come out of the gauge connected to; I believe you will see this makes the gauge show the voltage reading. For this test connect it as shown in the photo. The wires come out of the gauge for the light so that if you only want the gauge illuminated when the lights are on you can wire it into their circuit. Virgil did not come right out and say this but a voltmeter will not replace an ammeter in the tractor wiring and work. An ammeter carries a load through it where a voltmeter will not. The only amount of current a voltmeter will pass is what the circuitry in it requires to make the needle register, we are talking fractions of an amp. Bottom line is those studs you have the wires on will do nothing electrical they are intended to mount the gauge. They could provide a ground for a circuit but that would be a poor connection at best. You simply need to wire the tractor as shown in the diagram in the YT information I linked in my other reply. You will then be ADDING the voltmeter in as suggested powering it from a point that has 12 volt power when the ignition is on. The red and white wires that power the gauge illumination lamp can be wired to the small terminals as they are now to always light the gauge or they can be connected to the light circuit if you desire. If you are confused about where the wires go that were on the old ammeter they simply all connect together with a screw in the eyelets and can be taped up. If new wires are run the ammeter connection can be eliminated. So to do this disregard how the wire off the ..Bat.. post of the alternator is shown in YT diagram. That wire needs to be a #10 gauge directly to a positive battery connection, usually at the starter solenoid or mechanical starter switch terminal the plus battery cable connects to. From there power is run up to your instrument panel to connect to the ignition switch and the lights.
As far as your alternator it could likely be a ..one wire alternator.. since it has that plug cover on the 1 & 2 spade terminals. Old has added a way to test it to see if it can be wired as a 3 wire. I know often a one wire alternator has to be revved up high to start charging where a 3 wire will kick in to charge at an idle. You could wire it as a one wire and later change the alternator to a 3 wire if you find it does not function properly. Changing it to a 3 wire later requires minimal addition wiring and you only need to run one additional wire from the alternator to the ignition coil feed. Sorry this was long, just trying to cover all the bases so everything works correctly when you are done.
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This post was edited by used red MN on 05/07/2022 at 09:33 am.
 
Reading this again I need to correct or clarify:

Volt meter connection, one lead to ground and other lead to output of ignition switch.

Light in the volt meter is a night light. One side to ground and other side to output of the light switch. That way it is on only when lights are on. Ground connections on meter and light would match battery ground.
 
That photo of the wiring for the voltmeter did not come out real clear. Here is a link to a gauge that looks to have a similar configuration to what you are showing. There are more photos of it one of them is the wiring diagram. You have to swipe the photos on a phone or click the dots below on a PC to see them.
Similar voltmeter
 
That is a VOLTMETER and the two BIG BOLTS are just to mount it in the box.. The two small terminals are for the VOLTAGE READING... One terminal is connected to the ignition switch wire that is HOT when the key is on... The other terminal is grounded.....

Those TWO BIG WIRES are all wrong. Remove them and connect them together and TAPE.. That wire should run from the ALTERNATOR to the BATTERY terminals ( or hot starter stud)... You removed the amp meter that was INLINE... No longer needed. You may have damaged the alternator with the BIG WIRES connected to the voltmeter GROUND STRAP. ??

Alternator with ONE WIRE HOT does not use the #1-2 plugs.. Put the plastic cover back on it .
 
Thanks. The alternator is a Delco Remy with a label on it that says P7127M-3. The charging system on this tractor has never worked in charging the battery since I have owned it. I do not think it was ever working the way the PO had it set up. Correct on the voltmeter. I was trying to keep the wires straight and now realize they are wrong in the pic. I took the alternator into an auto store to have it tested. It would not pass (11.5v) when hooked up to the single wire output. We pulled the cap off and tried it in their config using their lead that plugged into the 1 and 2 outputs and it passed. I am under the impression that a single wire will not begin charging until you are at high RPMs. I am trying to avoid that. I am searching to see if this alt is a 1, run in 2(?), or three wire. Not having much luck.
 
I have a non directional indicator lamp I can put in line with the wire #1 pictured. Would this work? I have shown some pictures below. Bottom side of push-pull switch is #1 from alternator red, from coil blk, and voltmeter. Top side of switch is one to alternator post and the other to battery positive post. Other black voltmeter wire blk will join battery ground stud on frame. Does this look correct? Thank you.
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(quoted from post at 17:19:47 05/08/22) I have a non directional indicator lamp I can put in line with the wire #1 pictured. Would this work? I have shown some pictures below. Bottom side of push-pull switch is #1 from alternator red, from coil blk, and voltmeter. Top side of switch is one to alternator post and the other to battery positive post. Other black voltmeter wire blk will join battery ground stud on frame. Does this look correct? Thank you.
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The indicator light needs to be an incandescent bulb (replaceable type bulb). Is that what you have? It looks like it might be LED.

I believe 7127-3 is a style of Delco Remy alternator. The Delco part number would be 7 digits like 1103197, usually stamped in the case. The 7127-3 appears to be used in the part number for many aftermarket rebuilt and replacement alternators of that style. Almost all the descriptions say the alternator is not one wire capable. Can you see any name on the tag that has the part number on it? Then you could check to see what that manufacturer/rebuilder says about it.

This post was edited by Jim.ME on 05/08/2022 at 04:01 pm.
 
Yes, that looks to be wired correctly. As Jim said above the lamp will work if it is an incandescent bulb. You will probably never be able to determine if the alternator is setup as a
1 wire or a 3 wire by numbers. There are multiple outlets producing those one wire alternators. They just buy junkyard cores and rebuild them, so generally the numbers you see on the alternator are from whatever the alternator was originally installed on. The only difference between the one and three wire alternator is in the regulator, everything else is the same. The 2 spades 1 and 2 actually come out of the regulators. I attached a link to show you what the regulator looks like. Old has a suggested method to determine if the alternator will work as a 3 wire alternator. I will add a little tip here, when the alternator is charging the back bearing will have a pretty good magnetic pull. He did leave out one step I would add that if it is determined to work as a 3 wire I would check for a draw that would run down the battery. I use a test light with an incandescent bulb. Unhook the negative battery cable and place the test light between the post and the cable terminal. If it does not light the battery should not drain down. I am just happy to see that you did not connect your battery with wires on the voltmeter studs that may have been grounded and melt your new wiring.
Example regulator
 

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