I have a friend that's building '51 chevy cabover on a half ton frame. I'm going to help wire it and wanted a good source for a simple to understand and follow schematic. I have never wired a car from scratch and he has never done DC wiring plus he is colorblind.
This is a small block chevy with HEI, a 21 circuit aftermarket fuse block of unknown origin, GM style column of unknown origin, Classic Air HVAC system, GM style alternator, aftermarket in dash gauge set, and aftermarket bulb sockets for parking lights. Plus regular lights, radio, you get the picture.
Any advice would be appreciated.

You are going to need to find out what wire does what so finding wiring diagrams for the different things will be a must. Having knowledge of electrical circuits/components will help also.

fortunately the wires are printed on the insulation where they go. Some of these circuits will require a relay somewhere. I suppose it would be good to buy a relay bank and mount it like I've seen in some racecars.

what wiring kit is he going to use ?
hopefully not one of those "painful" kits................
having wired several vehicles by using rolls of different color and gauge wire "one wire at a time", although time consuming, it is not really a hard thing to do if one takes his time [lots of it !] and pays attention to the circuit's wants and routing.
there are several good diagrams out there one can use and be successful.
make sure you have a GOOD variety of QUALITY crimping tools, and know how to correctly solder a joint or connection when required.
quality terminals and terminal disconnect blocks are out there as well.
another "must" is making a detailed diagram of your harness so trouble shooting any problems in the future that may arise will be somewhat easy[ier] to do than "going in blind".

verify every wire in the system. Plenty of painless harnesses have had mislabeled wires in them... if it's a painless harness.

Suggestion, when making a run to the rear of the car for tails/markers, put weatherpacks in the run prior to where they all break out. This way if the right turn wire is really the left, all you need to do is flip it in the connector.

Layout is real important. Rough the fusebox in and run wires as close to intended path in the general direction required. Zip ties a plenty to clean up and mark locations of breakout from main runs.

Proper crimpers, not the autozone connector kit ones either... you'll need them.

Definately not a painless kit. Probably am ebay item.

Never really thought about that but could happen in anyones "kit".

To me this sounds like a classic case of paralyzed (paralysis ) by inaction. I am a expert at this.
Google: " a state of being unable to make a decision or take action due to overthinking or feeling overwhelmed."

The advice you have received so far is pretty much useless, if you had to ask in the first place how would you know know what it all meant?

Just do it ! (sorry)

I gotta disagree, no matter how much I think I know,
Whenever I read these post, there's usually something new/different I hadn't thought of.
That's the beauty of these forums, the wealth of wisdom.

I bought a car once that had been "completely rewired" all the wires were either red, or black, and none were labeled. That was fun trying to find a problem! I had to rewire it again.

From what I seen painless is for basic wiring needs. You may be able to fine one that would work but from what your description says some mods will be needed. I would look around and see what's available. Make a wiring diagram added to whatever you get for future reference. Another option would be to check out some early 80's cars wiring harnesses that maybe could be used. There you will already have many different wire colors and a factor wiring diagram. From that modify it to work with what you have. Years ago you could walk around junk yards and look for something like this, Today is another story.

any custom harness, either made from a kit, done one wire at a time, or used from an existing harness, needs a schematic for future use !
and do NOT use just one or two colors.............unless, of course you are a glutton for punishment !

GM sedan Del scratch wired.


Under seat Ford F1


Replace microcomputer seat controls with relays.

American Autowire highway 15 or 22 kits. Will require Specific crimpers. Probably have installed close to 50+ kits over the years more if you count the claasic update kits.
I do have an extra pair of the crimpers as I am winding down the business. PM me if interested. I've refused to put in PAINful kits as they are 💩💩💩.
You will get what you pay for

Maybe I didn't get across what I was asking. I was hoping someone had a similar project with similar components and had a link to or a just a hand drawn schematic laying around to post up.
I can wire it up but would it be done CORRECTLY is the issue.

Without information concerning the vehicle involved, and what wired components will be present, wiring schematics are pretty general. If you are considering making your own harness, most factory service manuals will provide a good basic schematic.

Be aware that a wiring schematic for a race car with minimum needs, or a simple street vehicle with just the basic points system, and a carburetor made to run, with headlights, taillights, functioning turn signals and a simple charging system, are both dramatically different then a wiring schematic for a 22 circuit breaker system, with EFI, and all the power accessories one could ever want. Every added electrical item increases the complexity of the system.

I thought I kinda did that in my original post. Anywho I did print out a schematic for a '79 chevy pickup and will sort through what I need.

in my experience, most harnesses on the market, especially the universal ones, are usually GM based, so having a schematic for something in that stable is usually very helpful in determining what can be used as is, and what needs to be rearranged.
just my personal life experience with these harnesses.
your mileage will vary.

Unfortunately to get a “simple to understand and follow schematic” you’re likely going to have to build it yourself as you go along.

“….I was hoping someone had a similar project with similar components and had a link to or a just a hand drawn schematic laying around to post up……” .

I’m in the process of turning an old race car into a street car (a 68 Valiant/Gen 1 Hemi project). I’ve got most of the wiring done (it’s a hybrid system using many of the factory harnesses along with some of custom built harnesses. While I could post up the diagrams, chances are there is very little that could be used on your truck without modifications.

I happen to agree with what moparx has said in his posts above. I have installed a couple of the harness kits over the years and have been less than impressed, for me it’s just easier to build my own.

I’m one of the crazies that actually used to enjoy wiring. Like moparx I’ve done several from scratch using several rolls of different color/gauges of wire (finding enough different colors can be a challenge in and of itself). The following is usually the way I go about it, basically the "system" that I use that works for me.

My first step it to list all electrical component (and in many cases purchase them) If there are some “someday” components I might wish to add in the future I usually include them on the list.

A word on component selection from a wiring standpoint, make it as easy on yourself as you can. You mention using a SBC engine, personally I would stay with an original style HEI distributor because of its simple 1 wire hookup (2 wires if you use a tach). Same with the GM alternator, a single wire alternator is really the way to go for simplicity. You might also find a quality universal headlight and ignition switches will be easier to wire than adapting factory units.

Speaking of switches is the ignition on the column or the dash and does it have a neutral safety switch at the bottom of the column, You will have to figure out what the application of the steering column is, you can figure out the wiring for the turn signal switch and other switches as applicable. With that you can look up the turn signal wiring and other switch wiring as applicable.

Almost any component you will buy will have wiring diagrams included. If you’re using components you already have on hand the internet is a good source for finding the correct wiring instructions.




Once I have the items identified I start drawing up the wiring diagrams for each system. Some can be pretty complex and others will be very simple. Here is are examples of one of the more complicated wiring diagrams and a simple one from my current project.

Wiring diagrams by M Patterson, on Flickr



As a mechanic when I build a car, serviceability is always in the back of my mind. When it comes to wiring that will include adding plugs on many of the harnesses to make the components easier to troubleshoot or replace.

On the gauge cluster you might notice there are two 8 pin plugs (16 circuits). The plugs will allow easier removal of the cluster (there was an additional 4 pin plug added after this picture was taken, when I added a couple more switches).

z AW2 by M Patterson, on Flickr

Normally I make separate harnesses for the lights and engine electrical at a minimum and these are always are on a plug where they pass thru the firewall.

On your specific project here are a couple hints that may help.

When you go from wiring diagram to actually building the system keep in mind the placement of the components and make them serviceable; things like turn and hazard flashers, horn relay and especially the fuse box need to be easily accessible once everything is done.

The SBCs especially the first gen ones have a nasty habit of the starter “heat soaking” causing a no crank situation in hot weather. Because of this when I do a project using these engines I normally add a remote starter solenoid. Here’s a link to a diagram to that.

https://maliburacing.com/remote-starter-solenoid-installation/

If you’re using certain components (GPS, Satellite Radio etc) and they have a large plug like the one shown.

12V to 5 V by M Patterson, on Flickr

Don’t be tempted to cut the plug off and hardwire it directly into the wiring harness. Inside the oversized plug are circuits to drop the output voltage from 12V to 5 V.

One last thing I normally do on a major car/tuck project is maintain a “Build Book” for the project as I go along. This is just a 3 ring binder with a lot of document protectors.

Z Build book by M Patterson, on Flickr

I usually include a build narrative, but more importantly it includes build specs and all the part numbers for the various components. All the instructions that come with the parts I’ve bought goes into the book along with all the wiring diagrams I generate. It may seem like overkill but if you’re going to keep the car for any length of time it’s definitely worth the effort (it’s also a nice selling point for when I eventually move the vehicle along.

I know it may all seem overwhelming, but remember you’re actually building it you’re just wiring 1 circuit at a time.

Anyway, just an old mans 2 cents.

i believe you would find American Autowires instructions to be exactly what your looking for and they have a good tech support if you would need it. f one can't follow their instructions they likely should not attempt the job. Not trying to be a jerk just stating an opinion.