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Technical Wiring from scratch: opinions/guidance welcome

Discussion in 'The Hokey Ass Message Board' started by 01mikep, Dec 10, 2015.

  1. 01mikep
    Joined: Jul 26, 2014
    Posts: 125

    from California

    I have been planning out how I want to wire this project with off the shelf components but not as a kit and decided to start a topic here to serve a couple purposes. First, I have several questions concerning best/most efficient way to run certain circuits and to gets second opinions/fact check my diagram/schematics before I run wire. Second reason for takin up your time with this post is to hopefully be a resource for others to reference as well. I plan to go circuit by circuit here.

    I’ll state that while I feel competent when it comes to wiring, I have never wired a car from scratch. At first I was going to buy a kit harness but none that I researched had what I was looking for without giving me excess that I didn’t need or would require me to have to add quite a bit to. I picked up a couple books on automotive wiring that turned out to be a pretty good review and gave some info I had not thought of before. Honestly, some of the best education I have found is right here on the H.A.M.B notably from Squirrel and Crazy Steve. There are other members that give good pointers/advice but these guys have been helping folks out here for years continuously on this topic.

    My project to wire is a fiberglass bodied T roadster that I am working to build to replicate the look of a 60’s Altered. Issue with this car is space, it does not have any. This build does not require a lot of powered accessories.

    I hope to continue this thread with a brief explanation of what I hope to accomplish, a diagram of how I would like to/or think is a good way do it, and hopefully feedback as to if it is a good plan or if I should consider a different approach. Warning: I tend to “overbuild” sometimes and feel I am starting to overthink this part of the build so pull me back if I need it.

    Power Distribution

    I am using two 6 circuit fuse panels (one constant and one switched power) both on interior on firewall, a Ford starter solenoid in the console, a universal 4 pole ignition switch in the console, an AGM Battery on the interior on the firewall, 10SI GM 3 wire alternator, 3 standard relays to feed.

    -Switched Power Fuse Box powers Fuel Pump relay trigger, Radiator Fan relay trigger, Trans Cooler Fan relay trigger, Gauges, and Tach.

    -Constant Power Fuse Box powers Horn, Headlight Switch, Haz/Turn Signal, Brake Light

    -Relays powered off of Battery/Alternator feed.

    -My question is how much over current protection does the power distribution part of the system need and what is the best method to do it. I would think I need to protect the feed to the Ignition Switch in turn protecting the feed to the Switched Power Fuse Box, protect the feed to the Constant Power Fuse Box, and protect the wire to the Alternator which feeds relays as well. Problem is what do I use for protection. Fusible Links inside the car would be a bad idea I think. Maxi Fuses are kind of bulky but I could hide or cover them. Below are a few ways I saw to wire this. Let me know your opinion.


    Option 1.JPG

    Option 2.JPG

    Option 3.JPG

    Option 4.JPG
    Last edited: Dec 10, 2015
    dos zetas likes this.
  2. My head hurts at the thought of a project like that. I have more money than time, so I went with a kit for my Ford. There were a lot of upgrades within the kit over what I had. I have a 50 amp maxi fuse in my wiring. Pretty basic and it protects everything from the solenoid back through the car.

    Attached Files:

    • FUSE.jpg
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    clem likes this.
  3. luckythirteenagogo
    Joined: Dec 28, 2012
    Posts: 1,265


    In my mind, doing it from scratch really isn't worth it. The kits you can buy have been planned out and include what you will need to do the job (and give you a list of other things you will need to purchase on your own). Most come with good detailed instructions and diagrams of where everything needs to be. The good ones even offer some level of tech support in case things get a bit sideways on you.
    While doing it yourself initially seems like a pretty straight forward task (meaning, get a few spools of wire, lay them out and hook them up, how hard can that be?) you'd be surprised by all of the little things that you need to get from A to B, and if you're not familiar with doing this kind of wiring, you are going to be in for a ton of research. So even if after all of that you still want to give it a go, by the time you buy everything you will need to do it yourself, you are most likely only going to be ahead a little bit of money from buy the kit. Oh yeah, when you buy everything yourself, you are going to wind up with a lot of parts you aren't going to use. Sometimes you only are going to need a couple connectors, but are going to have to buy a package of three times that. So after doing all of your research, planning everything out, buying all of your parts, laying it all out and getting everything connected and something doesn't work right, you have no real option but to scratch your head and grab a voltage meter.
    When I first started planning out my project I entertained the same thought. My opinion was how hard can this be? It's an old car with no computers and power nothing. It's a glorified go-cart. After looking into it a bit, yeah, I'm buying a kit for sure.
  4. squirrel
    Joined: Sep 23, 2004
    Posts: 50,939


    that's a lot of stuff for a 60s type build! :)

    I did my Chevy II with the stock gauge cluster, and stock front lights (both of which I re used some old original wires) and built the rest. I have only 3 fuses, and only one relay, which is the original type horn relay (it provides a nice handy stud for battery connections). But I also don't have modern electronics on the car, the only electric "race" type thing is the Holley fuel pump. I have a mechanical fan on the engine to keep things cool. That lets me get away with minimal wiring, and an early alternator, etc.

    I would start by looking at the current draw ratings of your fans and fuel pump.

  5. '51 Norm
    Joined: Dec 6, 2010
    Posts: 760

    '51 Norm
    from colorado

    I have wired several from scratch. It is the kinda thing that I do for a living.


    I'm looking for a kit for the next one.
    clem likes this.
  6. 55willys
    Joined: Dec 7, 2012
    Posts: 1,695


    I would buy a Centech fuse panel because it has all the circuits you need and lugs for power, Ign, acc and a ground bar to bring all your grounds to because of fiberglass. It also has turn and hazard flashers along with the horn relay being built in. It is about the smallest one you will find with those amenities.

    This is the only panel I like to use. You can buy it separately or with a kit. All the wires terminate at the panel and are screwed on by stripping the end and inserting it in the hole and tighten screw.

    The wire they use in their kits is crosslinked so it won't melt the coating off like pvc wire. I wire nearly every car that gos through our shop and I always use this panel and usually the kit but also wire from scratch.
    harpo1313 likes this.
  7. mike bowling
    Joined: Jan 1, 2013
    Posts: 3,558

    mike bowling

    I've bought pre-made stuff, and made my own.
    My roadster has a 10 pole fuse block that I'm probably only using half of -headlights, taillights, plate light( on/off -no high beams), brake lights, horn, and starter switch.
    I made this one up myself. Very simple ( although I had to use heavier wire than usual for the 6 volt system.)
    My coupe has high/ low beams, directional, horn, fan, etc. so I bought a 20 circuit harness from "E-Z Wire" for about $150. bucks and it worked out great. All wires are marked every 12" or so, flashers are included, and wire is "bundled" for front, rear, and dash. I didn't use all the circuits; coiled the wire up, zip tied it, and left the fuse out.
  8. Having done my own wiring from scratch and several different kits..... I'll stay with the kit.
    I really see no advantage to starting from square one.
    It's really nice if you have to repair something on the car later on and all the wiring is labeled.
  9. squirrel
    Joined: Sep 23, 2004
    Posts: 50,939


    As far as I can see, the big advantage of doing it from scratch is that you can make it look like it's from the 60s. But if you're adding a bunch of modern stuff, that's out the window...might as well give in and do it the easy way.
    clem likes this.
  10. Petejoe
    Joined: Nov 27, 2002
    Posts: 11,230

    from Zoar, Ohio

    My very first old car project from scratch was a 50 Chevy pickup back in the late 80's. In the course of saving to get three kids through college. At the time the only wiring kit that I knew of was a Ron Francis. Big bucks. So I decided to wire it totally from scratch. This truck had plenty of circuits planned as this was close to a street rod. I must admit. I learned everything I needed to know about wiring a vehicle in the course of 3 months. Every evening planning the knew circuit and glued to a guide book. I used a used fuse box. Made a junction box and gathered miles of colored wire.
    I may have learned a lot but now in retrospect. I would never go through that exercise in patience just for the fun of it. The kits are so much better than anything I can create.

    Last edited: Dec 10, 2015
  11. Here the fuse panel I made for my '35 along with the wire harness "kit". Basic hot rod with a simple electrical system. Only modern stuff are a horn and ignition relay along with some relays to make a four wire signal switch work.
    fuse panel.jpg harness.jpg
  12. KoolKat-57
    Joined: Feb 22, 2010
    Posts: 3,043

    from Dublin, OH

    Determining fuse sizes are based on wire size #10 wire=30 amps
    #12 wire=20 amps
    #14 wire=15 amps
    # 16 wire=10 amps
    These are just guide lines to protect the wire feeding a given device.
    The main thing is don't burn the car up because of the wiring.
    Use a circuit breaker for the headlights.
  13. 01mikep
    Joined: Jul 26, 2014
    Posts: 125

    from California

    Thanks for the input. I have weighed the pros and cons and I'll be wiring this from components. While I'm not a wiring guru, I'm comfortable working with and thinking through it. I've worked in aircraft maintenance (A&P and USAF) for almost 20 years. That doesn't make me an electrician but I'm comfortable with this.

    I'm not wiring this to to save money but to be able to choose exactly what I want to use instead of what the kit comes with. I still have quite a few (100's) of non-insulated terminal ends of all sizes, transparent shrink wrap of all sizes, have the fuse blocks, and all my switches/relays/fuses. What I lack is a few junction blocks/posts/guidance here and there along the way.

    Big question I have right now is what method did you use to (kit or not) protect the wiring to the fuse box/alternator/ignition switch/relay power feeds. Did you use fusible links, Maxi fuse, MIDI fuse? Did you use one of these methods for each run? Keep in mind this is all inside the car and I'm leaning away from fusible links for this reason. I'm tempted to use a MIDI fuse since its smaller than a Maxi in size but is still a slow blow like a fusible link.

  14. squirrel
    Joined: Sep 23, 2004
    Posts: 50,939


    I used the very popular 1960s method. Nothing. There is no upholstery in my car, it has a steel body, and I have a fire extinguisher and some wrenches to disconnect the battery if something goes wrong...and I wired it very carefully.

    If you run a fusible link from the starter battery terminal, like they did on many 70s GMs, it will probably be adequate. Ford also used this method in the 70s-80s, connecting several fusible links to the starter relay on the inner fender. But it's kind of hard to know what size wire, and hence fusible link(s) to recommend, without a better idea of what the load is from your electric fans and other stuff.

    remember the fuse or fusible links or breakers are there to protect the wiring.
  15. GTS225
    Joined: Jul 2, 2006
    Posts: 1,203


    Black....12vdc- , (ground) Nothing else!
    Red......unswitched, unfused 12vdc power
    Orange.....fused 12vdc power
    All other colors are fair game. T'were me, I'd follow standard trailer wiring color code for the turn, running, and brake lights.
    If you color-code your entire harness, you won't have to trace it out when you do have a problem, unless it gets abraded somewhere by the chassis.
    I know, that will get a touch difficult, finding wire in multiple colors. There is the possibility that you can find some with tracers printed on the insulation. That would enable you to repeat using your chosen color coding for different circuits.

  16. squirrel
    Joined: Sep 23, 2004
    Posts: 50,939


    Many of the aftermarket harnesses seem to use the 1960s-70s GM color codes...

    Pink ignition circuit for gauges, coil, etc
    Brown accessories circuit
    Light Blue headlight power to dimmer sw, and Left Front Turn Signal
    Dark Blue right front turn, oil pressure gauge/switch
    Tan headlight low beam, fuel gauge sender
    Light Green headlight high beam, and back up lights
    Yellow left rear turn signal
    Dark Green right rear turn signal
    Black tail lights
    Purple starter solenoid and front park lights
    Last edited: Dec 10, 2015
  17. David Gersic
    Joined: Feb 15, 2015
    Posts: 2,499

    David Gersic
    from DeKalb, IL

    If you don't follow something like a standard GM or Ford colour code, be sure to permanently label both ends of every wire, and draw out a complete circuit map. You won't remember exactly where everything is, and the next guy after you won't have any idea what you did.
  18. On my avatar I used Bob Miller's stuff from Rebel Wiring, not difficult, certainly not expensive.
  19. You might want to give this a read...

    It sounds like you at least have a grasp of the basics, which is good. There's multiple ways to wire these, some better than others and depending on how many electrical items you have and how big the loads are. While I started the thread with the most basic info, I do talk at length about harness design in the later posts.

    I'm personally not all that enamored with the 'kits' because of the built-in limitations/compromises most of them have. Start with a complete list of all electrical items and design the harness from there. DON'T start with a 'basic' harness and then try to add things.
    Last edited: Dec 10, 2015
  20. Crazy I read your how to wire thread and its a great tool. Thanks for taking the time to post.
    Terry aka dirt t
  21. Frank Carey
    Joined: Oct 15, 2009
    Posts: 549

    Frank Carey

    I wired my own car from scratch - including modifying a junkyard fuse panel. Create and maintain a detailed wiring diagram. I used a spiral bound notebook of graph paper pages. And write notes explaining anything that isn't obvious such as why there are two 12V feeds to the headlight switch or what keeps the wipers running until parked after you turn off the wiper switch or why there is a 12V wire to the dome light. I've got 70k miles and 25 years on my car and that spiral bound wiring book is a valuable record of what I did and why. Good luck and ask questions as you go.
    BradinNC likes this.
  22. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 2,283


    Piece of piss mate!
    You've won half the battle just by having the ability to draw up a schematic.

    The wires can be an awful tangled mess , but the important bit is the ends of the wires.

    very race-car I've owned I built a complete scratch built harness [several were road driven]
    I built a spec [NZ] IROC Camaro , that I managed to pull a lot of weight out just with the harness.
    The basic harness was 3x 7core trailer wire in a "Y" shape [L Fender, R Fender, and Rear] and everything worked to get it Road Legal .

    My Best advice is ....draw up a schematic ,and learn to load rate the wiring
  23. Jalopy Joker
    Joined: Sep 3, 2006
    Posts: 28,615

    Jalopy Joker

    what I learned on my first full wiring (no schematic) of a Hot Rod ('41 Chevy) is don't use the same color wiring for the entire job - Ha! I got everything to work, even figured out hot to use a toggle switch for the turn signals (there are aftermarket ones now). was showing my progress on bringing this ride back from the dead to a non-car builder friend. and pointed out the wiring, first thing he he asked was how did I know where what wire went where - right then I could have told him, later not so sure. live and learn (hopefully).
  24. 55willys
    Joined: Dec 7, 2012
    Posts: 1,695


    This is the wiring panel I was referring to.
  25. trollst
    Joined: Jan 27, 2012
    Posts: 2,087


    Funny thing....I just started wiring my 27 T from scratch today. Got a fuse panel out of a parts book for 25 bucks, two relays, one for the horn, one because I'm using an old style small headlite switch, relay will keep the lights bright without killing my switch, there is so little involved with a T that a kit didn't seem to matter, besides, I wire others cars often, got tons of supplies left over to use up. Go slow, do one circuit at a time, test each circuit as you go, you'll learn from it too.
    bct and firstinsteele like this.
  26. I used to take a lot of pride in being able to say I did everything on my car (except chrome plating). I kind of thought that was what it was all about. I guess the availability of easy aftermarket stuff has caused us to get lazy and I'll have to admit to having sold out some years ago by buying a 4 bar kit. Still, I'd rather do it myself.
  27. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    from florida

    For years I made up my own harnesses from scratch, but I used a Rebel kit on my 27 when I redid it about 8 years ago and really liked the fact that each wire was marked as to where it went. That being said, I am now back working in the marine business and can buy wire and components at my cost, so I am once again going back to wiring from scratch.

    The only thing I can add is, buy quality wiring and supplies (generally marine grade) instead of the stuff you buy at Autozone. It will last for years and is made for a wet environment . There is also no one, single best way to wire a car. There are some guidelines, but everyone has their own views and opinions on certain aspects of how to do it.

    Personally, I like Ancor and Blue Seas wire and components, they are first rate in quality.

  28. Tman
    Joined: Mar 2, 2001
    Posts: 36,064


    For most folks a basic kit will be the best way to go. Quality components just add up quickly going piecemeal. But, the OP sounds like he has a lot of that licked already so I would suggest doing it from scratch in this case.
  29. plywude
    Joined: Nov 3, 2008
    Posts: 699

    Member Emeritus
    from manteca ca

    I'm just finishing up a kit wiring job on my Chrysler 46, I have all ways done wiring from scratch but thought I'd try the kit, big mistake, when you do your own can make what you need and not waste your time on stuff you don't. Good source for electric parts is... Fry's Electronics in Fremont,Ca or Sacramento Ca they ship to you any thing electrical you need CHEAPPPPPPP...
  30. Blues4U
    Joined: Oct 1, 2015
    Posts: 6,466

    from So Cal

    To answer your original question, I would go with option 1. I don't see any reason to fuse protect a fuse panel! The other options add complexity and additional chances for component failure. I'm a big believer in the KISS theory of keeping things simple.

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