What Do You Think Of This Wiring? (alternator, Ignition Switch, Starter)

Lots of questions here...

I'm trying to install a 12SI, and working on cleaning up all the wiring at the same time. So far I've come up with this...

Does it look like it will work?
Also, I want to make sure I'm understanding the AMP light correctly... that it is installed in series (not grounded) with the number 1 exciter terminal from the 12SI? Can it be installed with the diode as well? Does the diode need to go on one side of the AMP light or the other? I realize they're providing a similar function... however I want the visible light.

 

Looks right to me.

Putting the bulb in series with the exciter wire eliminates the need for a diode. The bulb limits current enough that the alternator cannot back-feed through the bulb to the ignition swotch. The I terminal of the switch also goes to the coil, so it has to go off when the key is turned off. While running, the alternator holds terminal 1 of the alternator high - that's why the bulb goes off - both ends of the bulb are at 12V and there's no current flowing. If you turn the switch off and there's nothing to block current from the alternator to the switch, the engine keeps running, with the coil fed by the alternator. Clear?

 

Ok, yes it's becoming more clear.
Now, I assume I could also forgo the junction block and have all the ends at the starter +, might clutter things up a bit... but I don't see the difference if it's there or somewhere else.

 

Where would I install a voltmeter?

 

Why not eliminate the junction and attach everything attached to it to the starter? Less connections=less chances for problems, and simpler wiring.

 

You could ... depends on what the distance is to the starter connection. Not sure what the 134 looks like in this regard.

 

If I eliminate the junction block, then me thinks I should move the exciter wire to somewhere further down the line. I’d like it to be picking up the “working voltage”, this is why I don’t have it jumped right back to the alt+. Like Howard mentioned about the voltmeter, maybe the exciter should be at the IGN terminal. It’s essentially a bus block in my setup anyways...

 

You sure you mean the exciter wire? That has to go from 1 back to the ignition switch, so that it's turned off with the key. It's an "exciter" because it excites the alternator field at start-up, providing the initial magnetic field that starts the production of electricity. Once running, the alternator becomes self-exciting, using the generated electricity and engine power to make more electricity. If connected to the battery directly, the regulator electronics will continue to be hot when the key is off and it'll drain the battery.

The sense wire is the one that comes from 2. Jeep takes that directly back to the (+) connection on the alternator with a short wire. You can make the sense wire more accurate by either taking the wire as close as possible to the battery, or reducing the resistance between the battery and the alternator. The easiest way to do this is to use larger gauge wire. Jeep uses a 10 ga wire for the factory harness, but you could go to an 8 or 6 wire. You could also add a dedicated ground from the alternator back to as close to the battery ground as possible.

JMO - no need to be so fancy. If you want to run a long sense wire back to the starter terminal, that will be fine. Or you could copy Jeep and that would be fine too.

Regarding what Howard wrote about the voltmeter, he suggested connecting it to the I terminal so it will be off when the key is off. Again, this prevents the voltmeter from draining the battery (it is just a trickle, but it's something) - and it's an indication whether the switch is on or off. No need to worry about accuracy; the differences you'll see will be clearly visible if you just pick a convenient place to connect it.

 

Okay, it’s coming down to the “wire” and I’m installing the alternator idiot light. Well now I’m the idiot; How exactly is this wired?! There are both positive and negative wires from the socket, but I believe the light bulb socket grounds directly to the instrument cluster as well... is this an issue?

 

Yes. the socket needs to be isolated from ground. The light works by comparing the voltage from the alternator to the voltage from the switch. One connection to the alternator, the other to the switch. No ground. When the two connections are the same voltage (when the alternator is charging), the light goes out.

 

That is why I was concerned when the socket showed up with an all-metal casing, and the ground wire connected directly to it. How is the original setup completed? Maybe that’s an insulated receptacle on the cluster... time to put the coat on and go check

 

Yes that indicator socket is insulated. You will notice the oil and chg/alt sockets are the only two sockets that are like that. One wire to switched power and the other to term #1 on the alternator.

 

Well I just found that the socket I purchased can be insulated. There’s a small connector strap/ring that grounds the mounting flange to the negative wire. I removed this connecting ring, and now there is no connection between the mount surface and negative wire. Checked with Ohm meter.

 

Another question: In the above diagram, specifically the ignition switch, what path does current take to power all dash/accessory items? (I didn’t draw the ACC terminal on the switch). Does it come to the switch via the BATT terminal, in which case that’s a common bus with ACC?

 

Ok, answered my own question. The BATT terminal is in fact the main power source for all dash items while the Jeep is running. So in theory, I should use the largest gage wire I’ve got to connect BATT to the Starter + stud. I’ve got a roll of 8 awg... thoughts?

 

Probably overkill unless you have a monster alternator. The factory harnesses from the 70s and 80s use 10 ga for the charging wire. 10 ga connectors are more widely available. 10 ga to the dash is way heavier than needed.

 

I recently rewired an old Farmall tractor with lights and a few other add on bits. It already had a 12v conversion with a one wire 10SI. The original wiring was a fire looking for a time and place to happen. It was the first time I've ever dealt with a one wire alternator and I like it much better than having to deal with the extra wires. No fuss, no muss.