Think about the last time you had to crawl under the dash of your Street Stock race car to troubleshoot the electrics. Was it neat and clean, a place where you could easily find just what you wanted-and little else?
Or did it look like someone crammed it full of plastic-coated, colored pasta, with wires running in every direction and your being unsure of which ones went where . . . and why some made sparks and others didn't? We thought so.
There are Street Stock cars running today, probably at your local track, on which drivers simply use a pair of dykes to snip off anything coming through the firewall they don't want, and leave a wiring rat's nest of trouble under the dash. They run the risk of turning a minor electrical problem into a major meltdown.
Because the number of electrical circuits required is limited, the basic wiring on something like a Street Stock or Sportsman isn't difficult, and it doesn't have to be expensive. All it takes is a bit of time, thought, and attention to detail, just like any job that is done right.
Getting Started
Dennis Overholser, vice president of product development and technical services for Painless Performance Products, recommends you launch a new wiring job by getting rid of the old stuff. Painless makes wiring harnesses for street and race cars and sells the parts through local retailers for do-it-yourselfers to build their own.
Overholser says to begin your wiring project by pulling out the entire original wiring harness-every piece of it. "What's there is probably old and brittle, and with all the bumping, banging, and rubbing, you are likely to end up with a hole in it and have it short out," he says.
According to Overholser, everything you need to do a race car wiring job right should cost under $200. Here's what he recommends:
1. Move the Battery
If the rules allow, move the battery to the trunk. It helps balance the weight and gives you more room to work under the hood. Build or buy a strong battery box (see reference to bumping, banging, and rubbing under "Getting Started") and anchor it securely.
"For wiring the battery, I use a minimum one-gauge cable," Overholser says. "Don't get the cheap stuff with only a dozen wiring strands in it. Buy the finest cable you can find to get as much power as you can to the starter motor." Overholser says a good source for high-quality, fine-strand wire is welding supply shops.
"Run both the positive and negative cables all the way up to the engine," he recommends. "Don't skimp and just run the negative line to the framerail in the back of the car."
2. Install a Kill Switch
You'll have to decide-sometimes based on the rules of whatever group you are racing with-if the master kill switch needs to be installed on the positive or negative cable. The sanctioning body also will dictate where the master switch must be located. Some want it to be reached by a belted-in driver; others insist it be within reach of track safety personnel. Extension handles are available to do both.
While the positive cable runs to the starter motor, the negative side should be anchored directly to the engine block.
3. Protect Wiring With Grommets
"Every place a wire goes through the firewall or a framerail, it has to be protected with a grommet," says Overholser. "That's something you simply can't do without."
4. Use Fuses on Circuits
Most Street Stock cars won't carry many gauges. Most racers rely on a tachometer, oil and water pressure gauges, and an oil pressure warning light. Switches are usually limited to an off-on switch, and a push-button for the starter motor.
Overholser recommends these circuits be fused, using a high-quality fuse panel that can resist the jostling inside a car. "There are a lot of nice fuse holders out there," he says. "Look for one that is waterproof. One source for them is a boating supply house that specializes in severe duty applications.
"Some builders don't want fuses. That's their choice. For me, I figure a fuse only comes into play when there is a problem. At that point, what do you want to lose? Just the race, or the race and the car, too?" Make certain, Overholser says, that all fuses are rated high enough to carry the load. "Don't put a 10-amp fuse where there is a 25-amp current draw," he insists. "That's just asking for trouble."
5. Don't Scrimp on Switches
He continues, "The same goes for switches. Most guys are only buying a couple of them, so the cost isn't a big deal. You probably aren't going to find what you want at the local tune-up store where you buy them for $3.99. A good aircraft quality switch will run about $15. You just shouldn't scrimp on it."
6. Crimping Isn't Enough
Don't take shortcuts on making connections, either. "Crimp all connections first," Overholser advises. "Then solder them. Then use heat shrink over the connection to really secure them. One of the problems is that most racers hold a solder gun in their hands three or four times in their lives and don't know how to use one. They get the wires way too hot and the parts get crystallized and brittle. That's no good, either."
Overholser recommends using a low-temperature solder, keeping heat to a minimum, and using just enough solder to secure the connection. It makes sense to practice a few connections before winging it with a soldering iron if you've never held one before. This practice could save you some troubleshooting grief. His company uses a heat shrink tubing that has glue inside of it to secure the wire and terminal ends.
7. Use High-Temp Wire
Wires should be rated for high-temperature use. Most of the wire found in parts houses and discount auto stores is covered by PVC-type insulation and is rated for about 150 degrees F.
Overholser uses only TXL or SXL rated wire, with a cross-linked insulation and a 275 degree F rating. The difference between TXL and SXL is that the insulation on SXL wire is slightly thicker. "The wire with cross-linked insulation won't burn," he says. "It will melt, but won't burn. The PVC stuff will actually burn."
8. Add Spares
He says that when you are stringing wires under the dash and through bulkheads, it is a good idea to add a couple of extra ones, just in case you decide later to add an electric fan or some other accessory that will require power.
"It is a lot easier to have the wires there and not need them than it is to need them and not have them there," he says. "It's also a lot neater to do it all at once instead of adding more wire later."
9. Use Relays
If you do add a cooling fan, wire it in with a relay instead of right off a switch. "The relay will actually make the fan more efficient, so it will cool better," he says.
10. Use Eye Terminals
Overholser prefers eye terminal ends and screws in all his switches. He uses a drop of thread locker on each screw before cinching it tight. Others use liquid electrical tape that is painted on the terminals after everything is installed. A third option is a few drops of waterproof silicone sealer, which not only keeps the screws from backing out but also adds a bit of protection from moisture and dust.
11. Install a Quick-Disconnect Plug
Before actually building a wire harness, decide if you want to include a quick-disconnect plug behind the dash so it can be removed without having to disconnect the gauges and switches. "They aren't too expensive and can make getting to things a lot easier," Overholser says. "If you aren't likely to have to remove the dash to get at stuff behind it, there's probably no good reason to do it."
12. Secure the Harness
Examine the entire installed harness and use a generous number of tie-wraps to keep it from flopping around and getting chaffed. "Pay special attention to sources of heat," Overholser suggests. "Places where parts vibrate or any place where the harness could rub. The cheapest way to prevent damage from rubbing is to take some fuel or vacuum line and just slit it open and slide the wires inside to protect them."
13. Diagram Your Wiring
Lastly, take a few minutes to draw a simple wiring diagram. It doesn't have to have much detail. Include all the circuits, the color of the wires, where they go, and what they do. The pre-built Painless harnesses use wires labeled with their circuit use-starter, ignition coil, etc.-and these pre-marked wires are available through retailers.
Be sure to note any extra wires you strung to accommodate additions to the circuit. Keeping the diagram handy in a trailer or toolbox can save time and frustration at the track if electrical problems occur and you need to troubleshoot in a hurry.
Homemade Harness
Unless you run an auto electrical shop, about the only way you are going to get the quality of a professionally built wiring harness is to buy one.
If you run a Bomber, Street Stock, or Mini-Stock, chances are you probably don't have the budget for an eight-circuit race harness from Painless Performance or anywhere else.
But that doesn't mean you have to run something patched together that is a fire in waiting or something that looks like you built it on the way to the track. The off-season is the best time to tear into that wiring mess behind the dash and do it right. I built a six-circuit, fused system for a few dollars and it took only an afternoon to do.
First I determined how many circuits and switches I wanted. For the most basic of applications, the only switches you need are a main off-on switch, one for the ignition, and a push-button for the starter.
I figured six fused circuits would be more than enough to get power to the ignition coil, gauges, low oil pressure light, and tach. That left me with two circuits to be used as spares or as backup.
Here's what I bought and what it cost:
* Marine quality push-button starter switch: $4.99
* Two 50-amp off-on switches $9.98* Six-circuit fuse block: $12.99
* Fuses: $1.49* Push-on terminal ends: $1.99
* Screw-type terminal ends: $1.99* Assortment of shrink tube: $2.49
* 0.032 lead free solder: $2.99* Red warning light: $2.49
* Wire markers: $1.99* Package of rubber grommets: $2.19
* Liquid tape: $2.99
I had a supply of wire already on hand (I buy extra when it's on sale, so I always have some in the shop). You'll have to figure your own cost for wire. Remember, no one ever wishes for smaller gauge wire when circuits get hot on race night, so buy big.
Sketch out your own wiring harness needs before you begin, and then design the control panel on paper. If you have limited space, do a mock-up in cardboard or stiff poster board first.
Because the one I built wasn't designed for a particular car, I put everything to the right side, assuming the material to the left would be filled with gauges when installed.
I used a scrap piece of aluminum bent to a convenient shape. The bends put the switches within easy reach, and the fuse block pointed toward the passenger-side door, where it would be easy to check and swap fuses from outside the car. I added a piece of slightly U-shaped aluminum behind the push-button switch to make it stronger. Drivers with gloves can really push on that button when they are in a hurry or frustrated.
After that, I followed all of Dennis Overholser's suggestions: I used a wire stripper rather than a knife (or my teeth) to bare the wire, took the factory coverings off the terminals, crimped and soldered all ends, and then used heat shrink tubing to cover them. Whenever possible, I used screw-on terminals, then painted over the screws with liquid tape.
If you have to make a splice in a circuit, strip and solder the splice and cover it with heat shrink. Finally, I marked each circuit with numbered tabs, then wrote down which color and number goes where.
No one will mistake the end product for something out of a Winston Cup car. It is simple, effective, and clean. And if it looks better than what you have in your race car now, it may be a good way to spend an off-season afternoon and eliminate electrical failures.