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I\'ve reported a few wiring harness problems, but they have all been stuff that can be fixed just by swapping a few pins on various connectors.Well, tonight I found the problem that has stopped me in my tracks. I had put the wiring harness in the aircraft, and I was connecting the various power and ground wires when I took a closer look at one of the wires. The GNS-430 Com power line is supposed to get a 10 amp fuse, but the wire is only 20 AWG. It needs to be 18 AWG if it is going to get a 10 amp fuse. If I had simply followed the notes that came with the harness, and I ever had a short, I could have a smoking wire before the fuse blew. If I use a 7 amp fuse to match the wire I could be looking at nuisance fuse blowing in service.So if any other builders read this, please pay close attention to the details of any vendor supplied wiring harness. Don\'t simply assume that it must be OK just because it comes from a reputable vendor. I have lost complete confidence in these wiring harnesses. I\'ll be contacting the avionics vendor tomorrow to see how we can sort things out.

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Given that I already knew about two problems in the wiring harness that came with the avionics, and that it would be much more difficult to fix problems after the harness was installed in the aircraft, I decided to do a complete check of the wiring harness now. So I spent several hours today with an ohmmeter and the various installation manuals checking which pins on which connectors were connected together. In the end I found four pairs of pins (eight wires total) that need to be swapped in the intercom harness. The pairs of pins should be easy to swap once I purchase a tool to extract pins from Molex connectors. I also have to short two pins together to fix the last problem - I still have to sort out how I am going to do that.

I'm not happy with the problems in the wiring harness, but I am glad I found them now rather than later. This problem is much easier to deal with sitting in a comfortable chair working at the work bench than it would be if I was reaching in from the front baggage up behind the instrument panel.

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I didn't get nearly as much done as I expected yesterday, as the Columbia accident was quite a distraction. It was a real shock when I learned about it, then I rushed to the computer to find out who was on board, fearing that one of the astronauts that we know could have been on board. I was quite relieved to learn that our friends were safe, but it is still a great tragedy for the families of those that were lost. God speed.

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Yesterday I deburred the holes for the flight instruments with a 2 inch diameter ScotchBrite wheel in a die grinder. The flight instruments are not all exactly the same size, so I had set the fly cutter to a size that suited the smallest instrument, which meant the rest of the instruments wouldn't quite fit. But, a few turns around each hole with the ScotchBrite wheel opened them up the additional few thousandths of an inch required to get the fit I wanted.

Next I used a nibbler, Dremel tool and needle files to make the cutouts for the knobs at the lower left corner of the altimeter and course deviation indicator.

Today I trial fit the instrument panel in the fuselage, and attacked the problem of moving a main power feeder cable that supplies power to the main bus fuseblock. The feeder line was going to interfere with the back end of the GNS-430 rack. I was fortunate to find that I had enough slack in the feed that I could "simply" reposition it a bit to remove slack in one area to create some extra length so I could reroute it around the avionics rack. The concept was simple enough, but the cable was attached to the forward part of the left landing gear box with an Adel clamp. The nut securing the clamp was inside the landing gear box, which really complicated things. I finally managed to get the job done by crawling into the forward fuselage.

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Earlier in the week I plugged my ACK A-30 Altitude Encoder into the wiring harness to confirm that it was working. However when I turned on the transponder, it seemed that it was not communicating with the altitude encoder, as the pressure altitude field was blank. I pored over the installation manuals for both devices, but didn't find any clues. I finally got out the ohmmeter and checked to see which pins on the encoder end of the harness were connected to which pins on the transponder end. I discovered that two pins on the encoder end were miswired. Once I swapped the two pins the encoder and transponder started talking to each other. I checked the altimeter setting, and calculated the pressure altitude. The encoder must be calibrated later to meet the regulatory requirements, but right out of the box it seems to be within 100 ft of the correct reading.

I did do a check to make sure that 12 volts was only present on the one correct pin before I plugged the wiring harness into the encoder, but I didn't do any other checks on it. This is the second problem I have found with the wiring harness (there is also a glitch with the intercom harness that I have yet to fix). I'm not upset with the avionics vendor, as mistakes happen, and I know I have the ultimate responsibility for the quality of anything that I install in this aircraft. But I did learn that I should do a complete check of premade wiring harnesses, rather than just assuming that they were fabricated correctly.

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Here is a shot of the instrument panel with the big holes rough cut. I've got to deburr them, and make cutouts at the corner for some instruments that have knobs coming out (altimeter, CDI, etc). That is going to be a bit finicky.

I'll wait until the get the wing nut fasteners I've ordered before I cut the big hole where the removable panel with the gyros will go.

If you look carefully you can see where the edge of the angle that attaches the right side of the avionics tray is just visible on the left side of the three left flight instruments. I intend to trim 1/4" off that angle to make clearance for those instruments.

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I spent Monday evening and much of Tuesday evening poring over catalogs, sorting out the details of all the little odds and ends that I need to order. The rest of Tuesday evening was spent fabricating a drill jig for the four holes that go at each corner of the 3 1/8 inch diameter instruments. For the 2 1/4 inch dia instruments, I measured and drilled each hole by hand, which worked, but was very time consuming.

I stole an idea on the RV-List from Jim Oke:

"I made my own template out of a scrap of .040 or so 4130 (could have been 2024, of course).

Draw an X with the legs at 90 degs, then two concentric circles at 1 5/16" and 1 3/4". Drill #40 where all the lines cross - nine holes in total. (The Aircraft Spruce and Spec catalog has a diagram if you need more layout info.)

Lay out your panel marking where the center of each instrument face will lie. Drill #40 at these locations. Cleco the template in place at the center hole, make sure everything is square, then drill the four holes at the small or large circle as needed.

Then set you fly cutter as reqd and cut the instrument cut-out using the center hole as a guide.

Do a few test holes in scrap first to make sure your layout is accurate before you start on your actual panel. :-)

The only change I made was to make the hole in the middle 1/4" diameter, the same size as the drill in my fly cutter. It worked great.

Yesterday evening I spent an amazing amount of time trying to get the fly cutter adjusted to make a hole the right size. I could make holes that were a bit too big, or a bit too small, but I kept missing the happy medium. I must of made a dozen trial runs in scraps of wood or aluminum before I finally got it adjusted.

This morning before going to work I carefully marked where each big instrument should go, and this evening I cut all the holes (except for the attitude indicator and directional gyro, which will go on a removable panel). Pictures sometime this weekend.

This morning before going to work I carefully marked where each big instrument should go, and this evening I cut all the holes (except for the attitude indicator and directional gyro, which will go on a removable panel). Pictures sometime this weekend.