Creating a racecar wiring harness from scratch: How are you guys doing it?

Hi, guys.

The engine for my 190 Cosworth vintage racer will soon be back from the builders. I'll be switching from Bosch CIS/K-Jet to a pair of Weber 48 DCO/SP carbs. Ignition will be controlled by the stock distributor.

It's a stripped-out race car, so the chassis harness will be minimal: headlights, taillights, turn signals, reverse lights, wipers, blower motor, and fuel pump should be sufficient. Engine harness "should" be a matter of starter, alternator, and ignition coil...unless I'm missing something.

So, what are you guys doing for wiring?

A google search reveals off-the-shelf wiring kits available from Painless, ISIS, Auto-Rod Controls, SpeedWire, and others. Are any of these recommended? Anyone ever done something like this?

P.S.: I'm pretty much an utter n00b at this kind of thing.

I've heard good things about the kits from Painless...most non-production-based race cars either have a kit-based harness, or if they were hit with a tsunami of cash, fully custom harnesses with mil-spec connectors.

delcity

FWIW, Ive never built my own harness. But Ive watched it be done. Essentially, my friend uses nylon clothesline rope to make a template. Install the engine and components.start running rope lengths between sensors and components, leaving about 2" extra length at each attaching point (between sensors and components). Be sure to label each rope wire like "ignition to starter" etc. Nylon rope can be melted together where wires would be soldered using a butane torch or even just a lighter. Pull the completed rope harness off the car and lay it up on a pegboard using wire ties to fasten it down in straight lines with the rope taught. Trace the lines onto the peg board and transfer the labels onto the board as well. Then cut the ropes away. Then you just rebuild the harness on the board following the traced lines. Be sure to leave enough slack (remember those 2" extra lengths you left in the rope?), or put connectors in places the harness will need to be separated for installation.

Ive seen my buddy create a no non sense harness like youre mentioning in a day using this method with almost no revisions necessary once he goes to install it in the car.

In reply to 4cylndrfury:

damnit that is a brilliant idea.

The suggestion above sounds like the trick if you want a true custom harmess. A buddy of mine spent well over a year sorting out a custom harness for his turbo CRX. I'm not that patient so I've looked at kits for my various projects which never got that far.

Wish I had thought of that. I used the " thread miles of wire everywhere and then cut and reroute as needed" method

Added a thread to the Tech Tips section...

What's the advantage of the nylon rope vs just building the harness in the car? Substitute wire for nylon rope and you've skipped a few steps. Definitely make sure you're using the correct length of wire, if you always add 2" you'll have a nice clean harness. If you add "oh, about THIS much" you'll end up with a scraggly beast.

I've modified production harnesses and built from scratch. If this chassis already has the body wiring in place, I'd leave it and just add the minimal engine wiring. Factory engineers spent a lot of time and money designing what's in there. Of course, this is from the guy who lost the lead in the Targa due to a factory relay failing...

If you're doing the latter, the key is the fusebox. Get one with integrated relays, it'll be much easier and cleaner. Something like this:
http://www.delcity.net/store/Sealed-Mini-Fuse-Panels/p_803796

Start off by drawing your layout if you don't have a high level of comfort with your car. In your list, you left out the gauges, any interior lights you may want for servicing the car at night, radios, power for data loggers, aux lights, etc. Even a simple harness gets busy in a hurry. Assign relays and fuses to each circuit so you know how many you'll need.

Make sure you use color-coded wires. It's best if you stick to an existing scheme, such as the universal LBC colors or the chassis of your car. My Miata, for example, doesn't have much Miata left in the wiring harness, but I can look up the remaining circuits by color. You can use all one color of wire if you label the ends, but I find that's less useful if you're trying to chase a particular wire through a bundle when troubleshooting.

A good source for quality wire with the appropriate colors is a factory harness. I've torn down a couple and I just coil the wires up and toss them in a box. Then, when I need a blue wire with a white stripe, I go to the box. In my experience, even 40-year-old British wires are solid where it's been protected from the elements and heat. The Japanese stuff I usually work with is like new even when 20 years old.

Loom the wires using something you can easily pull on and off. I've started using velcro strips instead of zip ties because you're less likely to nick a wire when removing them - and you make less of a mess. You can buy rolls of velcro at HF and home improvement stores. Make sure the wires won't vibrate much, that will cause problems in the future. Where they have to move - such as the jump from chassis to engine - make sure there's enough slack that they won't get pulled loose with engine movement. Allow for failed motor mounts. And of course, make sure they can't rub and short out.

Use good quality crimp connectors with heat shielding. These are my faves: http://www.delcity.net/store/Heat-Shrink-Butt-Connectors/p_801794. Use a proper ratcheting crimping tool and you'll never have a problem. For example, this one or one like it: http://www.delcity.net/store/Double-Insulated-Terminal-Crimp-Tool/p_665741

Soldering is more brittle and not my choice for a high-vibration environment, although this is something people feel strongly about. I do know that I never see solder joints in factory harnesses.

The advantage to using the nylon method is youre not soldering wires upside down between a firewall and the block, or behind an accessory belt etc etc. I would imagine trying to hold wires and use a ratcheting crimp tool would be equally as difficult in a tight environment.

Running the rope takes as much time as running wire, youre right. But, the final product could be a bit questionable building the harness on the car. Again, this is all what Ive seen, Ive never done it personally.

Timely as usual.

I was thinking about this for the LS the other day when I found 3 panels.

I'm planning on modifying the factory harness to get rid of all the power and luxo junk I won't need. Hopefully, I can get everything down to one or two panels.

4cylndrfury wrote: The advantage to using the nylon method is youre not soldering wires upside down between a firewall and the block, or behind an accessory belt etc etc. I would imagine trying to hold wires and use a ratcheting crimp tool would be equally as difficult in a tight environment. Running the rope takes as much time as running wire, youre right. But, the final product could be a bit questionable building the harness on the car. Again, this is all what Ive seen, Ive never done it personally.

I can see the reasoning, although in reality you can crimp in pretty tight quarters. The ratcheting tools are actually easier than the hardware store cheapie crimpers, as once you get a couple of clicks on it'll hold the connector for you. It's not a good plan to put crimps or connectors in difficult to access locations anyhow, it decreases serviceability. I'd prefer not to have a junction between the firewall and the block if possible.

Might I suggest circuit breakers rather than fuses? More money, but you can reset with the push of a button rather than constantly replacing fuses.

I found this to be good reading when I was investigating making a new harness for my RX7 hillclimb car.

http://www.rbracing-rsr.com/wiring_ecu.html

Keith Tanner wrote: What's the advantage of the nylon rope vs just building the harness in the car? Substitute wire for nylon rope and you've skipped a few steps. Definitely make sure you're using the correct length of wire, if you always add 2" you'll have a nice clean harness. If you add "oh, about THIS much" you'll end up with a scraggly beast. I've modified production harnesses and built from scratch. If this chassis already has the body wiring in place, I'd leave it and just add the minimal engine wiring. Factory engineers spent a lot of time and money designing what's in there. Of course, this is from the guy who lost the lead in the Targa due to a factory relay failing... If you're doing the latter, the key is the fusebox. Get one with integrated relays, it'll be much easier and cleaner. Something like this: http://www.delcity.net/store/Sealed-Mini-Fuse-Panels/p_803796 Start off by drawing your layout if you don't have a high level of comfort with your car. In your list, you left out the gauges, any interior lights you may want for servicing the car at night, radios, power for data loggers, aux lights, etc. Even a simple harness gets busy in a hurry. Assign relays and fuses to each circuit so you know how many you'll need. Make sure you use color-coded wires. It's best if you stick to an existing scheme, such as the universal LBC colors or the chassis of your car. My Miata, for example, doesn't have much Miata left in the wiring harness, but I can look up the remaining circuits by color. You can use all one color of wire if you label the ends, but I find that's less useful if you're trying to chase a particular wire through a bundle when troubleshooting. A good source for quality wire with the appropriate colors is a factory harness. I've torn down a couple and I just coil the wires up and toss them in a box. Then, when I need a blue wire with a white stripe, I go to the box. In my experience, even 40-year-old British wires are solid where it's been protected from the elements and heat. The Japanese stuff I usually work with is like new even when 20 years old. Loom the wires using something you can easily pull on and off. I've started using velcro strips instead of zip ties because you're less likely to nick a wire when removing them - and you make less of a mess. You can buy rolls of velcro at HF and home improvement stores. Make sure the wires won't vibrate much, that will cause problems in the future. Where they have to move - such as the jump from chassis to engine - make sure there's enough slack that they won't get pulled loose with engine movement. Allow for failed motor mounts. And of course, make sure they can't rub and short out. Use good quality crimp connectors with heat shielding. These are my faves: http://www.delcity.net/store/Heat-Shrink-Butt-Connectors/p_801794. Use a proper ratcheting crimping tool and you'll never have a problem. For example, this one or one like it: http://www.delcity.net/store/Double-Insulated-Terminal-Crimp-Tool/p_665741 Soldering is more brittle and not my choice for a high-vibration environment, although this is something people feel strongly about. I do know that I never see solder joints in factory harnesses.

I tore down an entire newish altima engine bay harness and have it all stuffed into a canister. Comes in handy all the time, for jumpers, helping a friend wire up an e fan, replacing a worn through section of a factory wire, etc. And I have every color and several different sizes. And it was free. lol

In reply to 4cylndrfury:

I've done something similar, but not exactly.

Instead of running the nylon line, I make a sketch of where I want the lines to run, including where they terminate. Then I take a tape measure to the car and measure it all.

Then transfer that to a board. And then ran the lines.

BTW, the board doesn't have to be a peg board- I had a piece of plywood laying around, and then used wood screws wherever there was an important location where the wire changed direction. Works fine, and you may have that.

The most recent job was on my '74 Alfa, which was a very simple harness. The first job was a engine harness for a dual module V12 prototype- learned a lot there.

Where I found the biggest "issue"- the prototype, I was able to use a very wide array of colors for the wires. As you can imagine, when the means are there, wire is easy to get. However, for the home job, getting good wires in a good variety of color is very difficult. Outside of the basic colors, multi colors are hard to find.

Connectors was interesting for me- I wasn't sure where I would find good blade connectors from the 70's. Very few places had them for sale- at least the good ones that crimped both the wire and the sheath. But Molex has everything. Everything. And an engineering sample from them will cover most everything. Call yourself LanEvo racing. you can get a sample of 100 connectors that way.

FWIW, I've seen pro shops- the ones we use for prototypes- they ALL use the method of laying it out on a build board, making the harness, and then trasferring that to the car. So a BIG + 1 to that method.

There are some sources for multicolored wire in this thread:

http://grassrootsmotorsports.com/forum/grm/wire-harness-reconstruction/66568/page1/

Definitely stick to a color scheme. My lemons car has red, black, white, and yellow....none of it means anything.

4cylndrfury wrote: The advantage to using the nylon method is youre not soldering wires upside down between a firewall and the block, or behind an accessory belt etc etc. I would imagine trying to hold wires and use a ratcheting crimp tool would be equally as difficult in a tight environment.

As I have experience completely re-wiring a Spitfire with a custom harness (from Advance Autowire which uses Lucas color standards), I can agree with this whole-heartedly. The result of me trying to make the harness in place is the wiring behind the dash is an absolute rats-nest-cluster-berk. I pity the poor guy who has to work on that car next (ex-g/f's car).

Crimping isn't the problem - trying to tie and wrap the wiring was pretty much impossible.

Bearing in mind part of the problem is the Advance kit has a number of wires pre-terminated on the power block, so trying to tie everything into a pre-wired harness was a royal PITA. Some parts were easy - like the wiring going back to the rear of the car - because those wires were shipped seperate, so you could run everything, get it nice and neat, and then cut to length and make the terminations.

One real advantage to the painless and the like kits is that the left rear brake light, for example, has the words "left rear brake light" printed on it in tiny letters every couple of inches. Stumble across a wire somewhere and instantly know what it is.

An old friend of mine runs the Ez2wire website and while a lot of his harnesses aren't much cheaper than eBay at least he has used his products and will offer support after the fact. The basic Kwik Wire harness he sells for $200 and I think it is a pretty good price for a cars worth of wire if you are starting from scratch.

In reply to oldopelguy:

Even if one uses a painless, it would be worth the time to lay the harness out on a board.

BTW, one reason I did NOT use a painless harness- fuses vs. breakers. I wanted breakers, and found a set of marine breakers for cheap. The other reason was that I wanted something inbetween the 10 and 21 circuit set.

Ian F wrote: Bearing in mind part of the problem is the Advance kit has a number of wires pre-terminated on the power block, so trying to tie everything into a pre-wired harness was a royal PITA. Some parts were easy - like the wiring going back to the rear of the car - because those wires were shipped seperate, so you could run everything, get it nice and neat, and then cut to length and make the terminations.

This is why the big-money crowd uses mil-spec connectors to make modular harnesses. The "grassroots" alternative is to pick up some DB9/DB25/DB50 connectors from a computer store...it's not blingy and doesn't include an everything-proof seal, but it works.

If you do use computer connectors, make sure they can handle the power of your circuits. Fine for sensors, maybe not so much for headlights.

DaveEstey wrote: Might I suggest circuit breakers rather than fuses? More money, but you can reset with the push of a button rather than constantly replacing fuses.

I did that on one of my cars. It's far less space efficient, as you can't find a block as easily so they all line up on the firewall. It's tough to make the wiring behind them neat and tidy, IMO. But it's really easy to find if a circuit has tripped.

One note, of course, if you're constantly replacing fuses you should be dealing with the problem! If you're trouble-shooting and trying to find out why a circuit keeps tripping, you could use a circuit breaker as a fuse with a couple of short leads.

I've never used a Painless kit because there's always stuff missing that I need. I'd have to make so many modifications to their kits that it wouldn't be worthwhile.

I'm pretty sure I've seen a source for a full set of Lucas-coded wires. That was back when I started working on the Land Rover (on which I learned most of these lessons the hard way), so look at Rover sources if you want to find it :)

In reply to GameboyRMH:

Maybe in a car with under-dash room, but in a Spitfire there is no room for additional connectors. The power block didn't really fit in the first place.

It turned out the designer had never actually attempted to fit his harness in a Spitfire and based the compatibility on the fact the wiring diagram is essentially identical to a MGB. Shortly after I started working on the installation and bombarding him with questions, Spitfires were removed as an installation option.

Keith Tanner wrote: I'm pretty sure I've seen a source for a full set of Lucas-coded wires.

www.britishwiring.com