If you do not know what gauge of wire to use, you should not be making your own harness!  Get one already made - you will know the wires are sized properly and are plug and play.

If your going to have multiple head lights, you need bigger.. A BIG light might be 60 watts... X 2 is 120 watts... at 12 volts thats 10 amps... 16 gauge would be marginal.

As Steve mentioned, lighting circuitry along with ignition circuitry 14 ga is perfect. A little heavier than normal, but that's what I use through my wiring systems. For the Alternator, a 14 gauge fuse link off the output stud at the rear of the Alternator connected to a 10 gauge output wire will protect the Alternator if a short occurs. Being the small "D" series Tractors don't have a lot of accessories on them that pull big power, the 10 gauge output wire will work fine. Always go two gauge sizes down when using a fuse link. Also, a good place to install a 16 gauge fuse link would be at the Battery side of the Starter Solenoid that feeds the Ignition switch power. This protects both ends of the system. 12 gauge circuit for the Battery feed to the switch.  If you're wiring up an Alternator, go with the three wire system. Much better for Tractors that work in the low rpm range.   HTH  Thanks Den for the referral.  Wow Myron, pretty rude dude!  If offer wiring systems if interested.

Steve@B&B

Thanks @den for the suggestion, I will reference the link.

@Steve(ill) thanks for the guide, that will be super helpful. thats a great point about making sure it will fit through openings and the panel. I was thinking of going super overboard and making a 16 pin bulk connector so i can easily remove the gauge panel, removing it with the short wire lengths was really a pain in the butt. 

@Steve(NJ) in regards to your fuse suggestion, more protection couldn't hurt. Fuses are cheap, right now the only fuse on the tractor is for the lights. As far as I could tell for an alternator I can't see why you couldn't use a automotive one rated for the same AMP level? Most sites only have a one wire alternator choice. 

If you want to learn a lot about wiring, take a visit to our website. Up on the top header you'll see "More". When you go to that, a drop down window appears. "More Technical Info" is what you want to click on. Go into that category, roll down and start reading. There's a lot of information that I wrote many years ago in Hotrod & Streetrod magazines that is still all the same information that pertains to your Tractor as well. If you want to learn, there's a good start! Educate yourself. Makes for a good read. The difference between one wire and three wire systems, Voltmeter vs Ammeter, types of Alternators and how to ID them, wire gauge sizes-what and where to use them etc.   Read all of that, learn, then design your wiring system. Doesn't cost ya a dime, just a little time...... 

Steve@B&B

Alright experts, please be patient with me as I know there are a lot of wire diagrams for the D14 out on the internet. This is how my brain works, i have to see it and understand it before i do it. If you could verify I have drawn it correctly before I start ordering wire and parts. I was going to draw this a couple more times to get it more neat but I didn't think i was going to improve any.

My only question, does the solenoid need to be replaced to a 12volt?

Yes, solenoid either needs to be replaced OR add a resistor in series.You measure the solenoid coil's resistance (mine was 3.2 ohms ) , just buy a 3 ohm, 10 watt resistor and add it in series. Now the 'math' says 6 volts / 3 ohms= 2 amps. 2 amps x 6 volts = 12 watts ..but.... you're not applying power for too long, so resistor doesn't heat up. A 3 ohm, 25 watt resistor is 'technically' better..... I used what I had.

I just did this last month when Troy's starter finally 'bit the bullet', naturally that was 4 days after I'd sold Milton, who had a new starter in him......Since Troy IS a '57 it's a 6 volt system and the easy option was to just get a new 6 volt starter, which has a 6 volt solenoid.

something like this... but as mentioned, i would use 14 gauge wire instead of 16.