If electricity strikes you as mysterious, you're not alone. A device stymied an electrical engineer friend of mine not because it wouldn't work when it should, but because it worked when it shouldn't. He shrugged and conceded, "I guess it's running on 'FM.'" We're not at liberty to expand upon the first part of that acronym, but the "M" stood for magic.
Really it's no surprise that electricity intimidates us; we've been conditioned since birth to fear it. It's invisible, and since it's potentially fatal at wall voltage it's regulated pretty heavily. So whenever a light flickers or a fan stops blowing in our cars, we tend to revert to helpless mode and hope we meet somebody who understands "FM."
Only electricity really isn't magic. Like most seemingly complicated things, automotive electrical systems are collections of very simple assemblies. And lucky for us, there's no secret as to how these things work. It boils down to basic technique. Do a few things right and you're assured many trouble-free years of service.
We asked a few experts for some tips. We got them, but we learned something probably more important than the right way: the wrong way. These pros see and hear about every mistake made.
By no means should you think less of yourself if you've ever strayed; I've spoken "FM" for a number of years and have repaired my fair share of wiring systems yet I've still committed some of these indiscretions-some recently, in fact.
1. Get down to earth
As they say, fail to plan...
As they say, fail to plan and you can plan on failing. After mounting the switches and panel, sketch a system layout complete with run lengths. It'll prevent headaches and yield a far more professional-looking job.
According to Dennis Overholser, we pay a lot of attention to the hot side of the electrical circuit. But for a component to work it needs a complete circuit and that means a good ground. "Grounding is the number one cause for problems," he says. "If something stops working or just doesn't work right, it's usually a ground problem. We'll get calls like, 'I turn my headlights on and the turn signal indicators on my dash light up.' Well sure enough, if the headlights don't have a sufficient ground, they're going to try to ground through anything, even the turn signal lights."
"Especially today when people are putting batteries in the back, the worst thing they can do is ground that battery in a body bolt," Affordable Street Rod's Rich Fox revealed. "The best thing you can do is run a grommet through the floor and take that ground cable and stick it on the tailshaft on the transmission or run it to a bellhousing bolt."
Naturally the chassis and body need to ground on the same component, but Fox suggested grounding critical components like the headlights, taillights, and dashboard directly to the engine block or transmission. "Some guys want a grounding bar, but it's not really necessary," he says. "You can pick a spot under the dash, stick a 1/4-20 bolt on there and tighten a nut on it. Then put all your grounds on there, including the one that goes to the engine block, and put it on that ground bolt. Then tighten a second nut on there and you're ready to go." Haywire's Ken Logue concluded, "Your system is only as good as the grounds."
2. Lay out first, terminate last
It stands to reason that the...
It stands to reason that the engine or transmission deserves the battery-grounding cable since the starter demands the most of the electrical system and electronic engine management systems require consistent power. The engine or transmission then serves as an adequate ground for the chassis and body.
Overholser said the first mistake hobbyists make is terminating wires before they route them in the car. "They cut the wires too short," he noted. Instead, he recommends installing the panel first, all electrical components second (switches, lights, gauges), routing and securing the wires third, and terminating them as the final procedure. "It just makes things so much easier," he noted.
"Try to keep the electrical in the upper driver side of the cowl," Fox said. "In a T-bucket under the seat is about the best. I don't recommend mounting fuse panels in the trunk because it puts way too much wire in the system and way too much voltage loss by stretching the wires out way too long."
3. Isolate the system
Consider ANL fuses to protect...
Consider ANL fuses to protect the entire system. The mini ANL fuses handle as much as 175 amps and their popularity among audiophiles means fuses are common and inexpensive. Haywire offers a dual-fuse mini ANL holder to isolate the alternator and the electrical system. The built-in voltage readout is a handy bonus.
Each fuse in a system may protect an individual circuit, but the wire that feeds the system needs its own protection. Each means of protection has its advocates, however, Overholser summed up the idea: "That wire needs something to protect it." Logue put a finer point on it: "It's supposed to go by the power source to protect the system. It doesn't do anything if it's inside the car next to the fuse panel. A fuse or fusible link doesn't protect the fuse panel; it protects the wire that feeds it."
Alternators can leave the building in dramatic and sometimes disastrous ways, according to Overholser. "It's very common for the diode bridge to go out, and when it does the alternator shorts out. Well if they don't have the alternator circuitry and so forth protected-poof!-wires and everything else go up in smoke."
4. Don't gang up on circuits
All the accessories and powerful...
All the accessories and powerful headlights available today make it easy to overload even the best switch. Relays, on the other hand, handle far greater loads. When used as triggers for relays, even the weakest switch will last forever.
As the saying goes, you're never done with a car until you sell it or die. Whether changing or adding to them, we often add components to existing circuits.
While OEM and aftermarket wiring manufacturers alike combine multiple devices on single circuits, they take various things like current draw, wire gauge, and fuse capacity into consideration. For example, adding accessories to an existing circuit may require a greater-capacity fuse, which may cause problems if that fuse's capacity exceeds the capacity of any single wire in that circuit. Should a wire find ground or its accessory fail in such a case, the wire may catch fire without ever blowing its circuit's fuse.
"If a fuse panel is labeled to take a 15- or 10-amp fuse, don't over-fuse that circuit because the wire for that circuit is that way for a reason," Fox said. "That's why they say that it takes a 10- or a 15-amp fuse because that's what the wires in that circuit can handle. When people put a bigger fuse in because the circuit keeps blowing, all they're doing is making the system hotter."
Instead, consider an accessory fuse block. Better yet, if you're contemplating a new wiring kit, take a tip from It's a Snap's Rick Souza: "Go with a bigger panel; it's just a few extra wires, and you'd rather have a few extra wires than not enough. In most cases people need a system bigger than they thought."
5. Conventional Versus one-wire alternators
If on the fence when shopping...
If on the fence when shopping fuse panels, go bigger. Even though this panel has only 13 circuits, it's nowhere close to running out of either switched or constant power options. Technically the driver side cowl is a better mounting location, but I chose the passenger side for accessibility. I'll never run A/C anyway.
This isn't so much of a problem as an explanation. "People will call in and say 'My voltmeter in my dash only reads 11 volts,'" Overholser says. "Well the first thing we'll ask them is if they have a one-wire alternator. Ninety-nine times out of 100 they'll say yes."
There's nothing wrong with a one-wire alternator but theoretically they aren't as effective as their OEM-style counterparts of equal capacity. It's because one of the additional wires in an OEM-style alternator senses the system voltage. "It measures the voltage level in the fuse block where the system gets its power," Overholser said. That's important because the alternator can compensate for any voltage-killing resistance in the wire that feeds the panel.
"Without the sensing wire, the alternator doesn't know any different. A one-wire alternator is a convenience module. It'll work but it'll never work quite as well (as a conventional three-wire alternator)," Overholser concluded.
If you run out of fuse options,...
If you run out of fuse options, get an accessory fuse block. Nearly all wiring vendors sell one and some even clip together. Wire these directly into the battery for fused power (remember the fuse at the battery). For switched power consider giving it battery power by way of a relay to prevent overloading the ignition switch.
I'm no pro, but I should still...
I'm no pro, but I should still know better than to link my alternator sense wire directly to the alternator output. Now the alternator can't compensate for the resistance in the wire that feeds the electrical system. The world still spins on its axis, but my headlights and ignition system will never operate at 100 percent.
These gauges look alike, but...
These gauges look alike, but the voltmeter in the foreground is safer and better reads the electrical system's condition. If you run an ammeter, ensure that it's a shunted type and its capacity is greater than the alternator's.