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Alternator Wire Gauge

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vtsteve View Drop Down
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    Posted: 16 May 2022 at 9:18am
I've been working on building a wiring harness for my M-38 project. I started with Painless Wirings universal weatherproof off-road harness (link below). When they say "universal", they mean it. I have a spider web of bundles in my garage which I will trim down once I put the system in the jeep--I have my back end run, headlight run, gauge run, battery run, turn signal run, etc. all bundled up independently. I think it will be a good setup and I will share a nice wiring diagram when done. Aside from the fuse block which I will mount on the driver side firewall, it should look pretty low key.

My main question--I'm going to re-use the alternator that was on the jeep when I bought it. It put out a healthy 13.4 volts. The alternator had a FLD and BAT connection--the BAT terminal went back to the hot starter post. The FLD went to a voltage regulator which then went to the ignition connection on the key switch. When disassembling the wiring, I noticed that the (thin gauge) wires that Bubba installed had some melting--I knew they were undersized.

Question--what gauge wire does everyone recommend for:

1) Alternator BAT terminal to BAT (in this case, hot post on starter)--I'm thinking 6 gauge protected by a 70 amp midi fuse)
2) Alternator FLD to External Voltage Regulator (I have no idea how many amps this would carry)
3) External Voltage Regulator to IGN circuit (same as 2--I have no idea how many amps this will carry).

https://www.painlessperformance.com/wc/10144
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vtsteve View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vtsteve Quote  Post ReplyReply Direct Link To This Post Posted: 16 May 2022 at 9:52am
The diagram below shows how it was wired up originally. Note I have X-d out the FLD-GROUND, as it didn't have this connection. I'm planning to maintain this same configuration (unless recommended otherwise), and need to know suggested wire gauges. I can't see too much amperage going through the regulator to the ignition circuit, but I could be wrong?

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JohnB View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JohnB Quote  Post ReplyReply Direct Link To This Post Posted: 16 May 2022 at 11:07am
My 12v set up that seems to work. I installed 30A inline fuses and none have popped yet. I use a started button on the dash to the solenoid. Tracers on the wire cover tell you the gauge. I purchased this wire from Rhode Island Wire. Because I didn’t plan on any big electrical demand, I’m using a small 50-60A alternator. 
I used a white board to work out my wiring plan. Had to make many changes to it before I ran and cut wire. 


Edited by JohnB - 17 May 2022 at 9:50am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cpt logger Quote  Post ReplyReply Direct Link To This Post Posted: 16 May 2022 at 11:30pm
I have not looked up what Dodge used for the wire gauge for both #2 & #3. Yet IIRC, They were 14 gauge. Look it up for any 1960-1990 Dodge/Mopar.

I like your overkill with wire #1. On my 1965 Dodge Dart, it used to be #10 gauge. When I replaced it I used #8 gauge.

I am a big fan of having good grounds. When I started having issues with the Dodge voltage regulator, I ran a separate #10 ground wire from the alternator to the regulator to the battery negative cable. Doing that seemed to help with my regulator problems. It is cheap & easy. It also can not hurt. Some would say it is kinda like wearing a belt and suspenders. I say as I am wearing both right now.Smile 

I am not a fan of using the battery clamps that bolt onto the cable as you have now. That connection is a known place for corrosion to hide. If it gets a little wet & stays that way for a while it can start to corrode and not show it from the outside. It used to be a fairly common issue when I lived in the PNW, especially near the beach. Even here in the high desert where I am now, I always buy the one piece battery cables. I also go up at least one gauge size when I replace them. I am paranoid that way.

On 6 volt applications I try to always use at least OO gauge cables. It gets fairly cold here on the winter nights.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vtsteve Quote  Post ReplyReply Direct Link To This Post Posted: 17 May 2022 at 9:25am
CPT, yea, I'm trying to do my homework. To be honest, I'm a bit disappointed in the painless harness. It has 16 gauge wires feeding 35 amp relays, which should require an 8-10 gauge (assuming a 12-volt system like I have). It has take some thinking on which circuits can run though which wires/fuses based on amperage, and wire gauge. I always try to make sure all wires are protected by a fuse.

I'm doing the same diligence on the grounds with regards to wire sizing.

I once saw a guy at a 7-11 with a freshly restored VT Beetle. It caught on fire. Who knows if it was electrical, but I don't want to be that guy.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote drm101 Quote  Post ReplyReply Direct Link To This Post Posted: 17 May 2022 at 9:38am
Wire gage for the alternator output depends on the current capability of the alternator. The current will be at it's max when the battery is low and the alternator spinning above idle speed. If the battery never gets low, you can run a 14 gage wire and not have an issue, but the first time you run the battery down, then jump start it and the alternator spins up, you'll be pushing a ton of current and that 14 gage will light on fire. A 250 amp alternator will light it on fire much quicker than a 35 amp alternator.  
Dean
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jeepsterjim Quote  Post ReplyReply Direct Link To This Post Posted: 17 May 2022 at 11:38am
My experience with ALT. wiring came around when working on Jeepster Commandos which had the same basic Alt/starting system as the late '60's chevy trucks....underrated!  Jeep used 12 ga., unfused, wire from the Alt to the BATT terminal at the ing switch. CJ5, Jeepster Commando owners ever come across a burnt ing switch?  AMC/Jeep upgraded the ALT wire to 10ga in'72 and it solved a lot of problems. 
SO, if one is going to use a 80 AMP Alt. and no winch OR lite winch usage, 10ga wire should work. If one is planning moderate winch usage, 8ga would be the better choice. We ALWAYS put a fusible link near the Alt.
Jim
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vtsteve Quote  Post ReplyReply Direct Link To This Post Posted: 17 May 2022 at 12:14pm
Interesting. I would have assumed that amps from the alternator to battery would match amps running through the electrical system. Good to know.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cpt logger Quote  Post ReplyReply Direct Link To This Post Posted: 17 May 2022 at 2:48pm
As an old VW mechanic, I would bet that the Beetle that caught fire had an issue with the fuel line from the fuel pump to the carburetor. Folks usually install an in line filter with rubber hoses & do not consider both the heat & the vibration that little air cooled engine generates. There is a reason that VW put a steel fuel line in that location.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fl Cj guy Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2022 at 12:07pm

I preface my question with this statement: I have no idea what I’m doing.

 

I have so many questions about wiring in this alternator. I’ve gone 12v but clearly don’t know what I’m doing. I’ve read so many posts here and elsewhere but many of the older pictures are missing due to hosting problems from 10 year old threads. I’m a picture guy, I don’t know the terms for #, #2, etc.  My Cj2a wiring was mostly missing when I got it. I’ve taken this thing all the way to the frame and back up so I’m left with this last major issue. I know it runs so far because it was direct wired\jerry rigged to do shake down driving but I need it wired for real now.

 

I bought a Walck’s harness(no turn signals) and it is wired from the meter, to ignition, etc.  There are wires coming through the firewall from the back of the meter. One is to the coil ( no issue here). One is to the floor starter switch with the odd termination fitting, and the longest one is “to alternator”.  I don’t know what to do with these wires or where they go. I’m asking for help because I’m not a fan of sparks or being shocked.

 

Attached is a pic of the piece of harness coming through the firewall and how it looks on my 2A but the pics are screen shots from youtube. There is a picture of my alternator also attached. I do not have a solenoid.

 

Please tell me:

 

Does the small red wire run back to the post labelled “A”?

Does a wire go from the post “A” to the battery + terminal?

Should I be grounding post “B” somewhere to the frame?

Where does the longest wire “to alternator” attach to?

What is the white wire coming from alternator for?

Am I not asking questions that need to be asked or dealt with?

 

 

 

Please forgive my stupid questions. I'm new to this and I don't know better.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fl Cj guy Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2022 at 12:09pm
Please forgive my stupid questions. I'm new to this and I don't know better.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fl Cj guy Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2022 at 12:10pm
Please forgive my stupid questions. I'm new to this and I don't know better.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote otto Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2022 at 12:23pm
http://www.madelectrical.com/

I used this guy's kits before to wire the 3 wire system. It's pretty simple really; his website is very thorough with lots of information.

If you call him, he'll answer and is very knowledgeable, but carve out considerable time for the conversation.
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