CJ3A Wiring - JeepForum.com
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post #1 of 2 Old 06-16-2008, 09:42 AM Thread Starter
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1949 CJ3A 
Join Date: Jun 2008
Location: Edmonton, AB
Posts: 83
CJ3A Wiring

I cleaned up a lot of old wires out of my 1949 CJ3A over the weekend. I probably pulled more than half the wires out! (I left the wires to the rear lights in place, but they're fried and need to be pulled at some point.) All that's left is the engine (& gauges), front headlights (low beam only), and heater/wipers/washer. I didn't change any wiring that was there--only removed bad or unconnected stuff, and improved some connections. (Exception: I wired the lights on the gauge panel to the "acc" terminal on the key.)

This is a schematic of what the wiring looks like now (I haven't put dedicated grounds in yet, but I will). I left out the gauges except the ammeter and wire to the tach. I also left out the details on the heater/wiper/washer.

Note: It's a 12 V system now (not the original 6V). There are only two fuses in the entire system--the one 60A fuse that everything but the starter goes through, and a 30A fuse on the headlight circuit.

Also note: The "Acc" terminal on the key gets power when the key is in the "on" or "acc" position. The "on" terminal gets power when the key is in the "on" or "start" position. There is nothing currently connected to the "start" terminal, as this Jeep has no solenoid--there's a foot activated mechanical switch on the starter. (The same pedal pushes the pinion into the ring gear--it's not intertial.)

I have a couple of questions:

1. The output wire from the alternator loops back to one of the terminals on the side. This is just a short loop. I've read where Jeephammer said that's incorrect. Where should it go?

2. The other small wire to the alternator goes directly from the "on" terminal on the key. There's no diode or light in between, as shown in Jeephammer's diagram. The ammeter is in the circuit between the battery and the key, though. Does the ammeter serve the same purpose?

3. When the engine is running, the ammeter is reading all the way to one side. That doesn't seem right! Is it a bad gauge, or is it wired incorrectly? (You can see on the diagram how two wires connect to one side of the gauge and one wire to the other.)

4. I don't know much about ignition systems. There's a block on the firewall which I assume is the primary resistor-labelled with a ? because it's just an assumption. I didn't measure its resistance. I read somewhere that this resistor should be bypassed during start. The engine starts now, so that's obviously not required, but would it help? Would it hurt anything? That's really easy to do, but I don't want to do it if it's a bad idea. Note that the CJ3A wiring diagram doesn't even show the resistor--Would it have been added when converted to 12V?

5. Anything else I've missed?

I will be adding dedicated grounds at some point. If you look at the picure at http://www.cj-3a.com/Starters&Ringgears.htm you can see a thin flange on the back of the starter. It's fairly thin, but conveniently located with a bolt hole in it--is it good enough for a starter ground wire, or do I need to connect it to something more substantial.

Jeephammer--I will also consider your suggestion of converting to electronic ignition, but not quite yet. (I'll post separately when I'm ready for that.)



Last edited by PaulS; 06-19-2008 at 09:38 AM.
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post #2 of 2 Old 06-19-2008, 09:42 AM Thread Starter
Registered User
1949 CJ3A 
Join Date: Jun 2008
Location: Edmonton, AB
Posts: 83
No responses?

I have a day off tomorrow, and I'm going to make some final adjustments before taking the Jeep out to the acreage where it will live at least for a while (hauling firewood and bombing around the cutlines and trails). I'd like to do a full restore on it, but that will wait at least a year or two...

I'm going to pick up a cheap ammeter at Princess Auto to compare to the one in there... I think I will add a wire bypassing the primary resistor when the key is in the start position (unless someone can say why it's a bad idea). The nice thing about the wiring on this Jeep is that I don't need to use the bypass, as the Jeep can be started without turning the key to start--so I can very easily compare how it starts with and without the bypass.

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