When you're building a plane, you want to make sure that the project falls within your capabilities as a craftsman. And if you find yourself getting in over your head, you'll solicit help from those who have been there, done that.

That same commonsense approach should apply to the avionics that are destined to light up your panel. If you possess a good knowledge of electronics, you could do a complete installation. But if you tend to get lost in a maze of schematics, you'd do well to work with an avionics shop. You can still save on installation costs by building the tray mounts, laying cable and performing other grunt work, while getting the advantage of a shop's training and test equipment that could save you time and energy - and prevent you from making some very expensive toast.

I'm going to pass along some installation tips that were provided to me by Don Dominquez, part owner and manager of San Luis Avionics at the San Luis Obispo Airport in California.

Don is frank to acknowledge that most of his homebuilder customers buy their radios via mail-order. The cost is usually lower than going through a local shop, but if there's a problem with the box, the buyer is on his own. There are other pitfalls to long-distance buying. For example, I've seen ads from some mail-order outfits promoting GPS receivers that are no longer in production; these computerized sets get outdated in a hurry.

Before you decide how much of the installation you want to tackle on your own, Don suggests that you give yourself a quiz: Can I use hand crimpers? Do I know how to splice wire? Am I good at soldering? Have I ever assembled a BNC connector? What gauge wire do I need? What nuts, bolts, circuit breakers, lamps, switches and annunciators? What antennas?

Dominguez: "A nice way to start is to lay out a plan and think about the minimum requirements you have. Is it going to be a VFR or IFR aircraft; is there special equipment you want, such as a moving map display? You'll want to be sure the systems interface with each other. There's a lot of detail in parts acquisition. Think about the installation kits that you can get from the manufacturer.

"Then you have to get to your Budget Department and decide how much you want to spend, taking into account whatever professional help you will need.

"Now you've got your parts and you're ready to start installing. The first thing you want to think about is antenna placement. I see a lot of noisy (radio noise) airplanes, especially in experimentals with composite construction. You have to consider ground planes and the proximity of antennas - whether one antenna will be shadowing another. After you've got your antennas placed, you want to think about accessory placements: headphone and mike jacks, lamps, annunciators. Are the switches going to be easy to reach?"

Don advises buying high quality wire and fasteners, as well as the use of chafe guards, including grommets when you're running through holes. When laying cable, make sure the coax has no tight bends and is secured properly, so there won't be rubbing or chafing. Don't run the wires too tight; leave a little service loop in case you want to add something in the future, such as a lighting wire.

Proper cooling is essential to keep your valuable avionics healthy. Get a good aviation-type cooling fan; a cheaper unit, such as a computer fan, may cause such problems as static noise, hum and comm squelches breaking. Of course, have your cooling system in place before you install the radios. When you mount your trays, you'll want to think about backstraps for support, space between the trays, and running the cooling hose on the tray connectors.

Now comes the hard part, and here's Don with some more advice.

"You've got your trays mounted and you've got backstraps on there and the radios slide in the slots just the way you like them. Now you need to fabricate the harnesses to wire everything into the aircraft. Obviously, you need to be able to read the installation manual schematics and know what size wire you need for each purpose. Wires that are going to be running power and grounds are going to be typically a little bit larger than audio signal wires. You also want the right circuit breaker for the equipment it's protecting. Make sure you do whatever the manual tells you to do. If you don't install the radio properly - if you forget to cool it or you put the wrong voltage to it - you're going to lose your warranty.

"One of the first things you want to do before you put those radios in the racks is pin out the harness. You've got to make sure that you have your powers and the grounds on the right pins before you plug any radios in. A 20-minute check can save you thousands of dollars in smoked radios. Test it on the bench if at all possible, or take it to an avionics shop and ask them to plug in the radios and make sure that you've got it right. Get the bugs worked out before you put it in the aircraft, if you can.

"You've turned on the power and checked it out. Everything looks pretty good. Your next step is to have the local avionics shop with the ramp test equipment do a proper ops check. You want to be sure you have the right power on the transmitters, and the frequency, modulation and signals are functioning properly.

"It's nice if you can have a shop do the harnesses for you, if it's in the budget. It's pre-tested and everything is measured to length and your avionics package comes together really easy. You can also have a panel made for you by an avionics shop if you're not really good at laying out the instruments and cutting the holes for them, but that can get a little costly.

I asked Don if he provides assistance to his customers, and if so, does he charge for it?

Dominguez: "It depends on the degree of assistance. If it's a quick telephone call, I'll give them some advice, but if they want me to come down and inspect their airplane and I get tied up for an hour or so telling them where they should run the leads, etc., I'll have to charge them."

If you'd rather stick to airplane building and let the pros handle the complete avionics installation, there are shops that will deliver to your door a custom panel with all the radios in place, pre-wired and ready to play.