When I last flew MYRO it had a pretty good fit of instruments and gauges including the electric fuel pump, of course, and carburettor heat as well as all the usual items like an altimeter, airspeed gauge, cylinder head and exhaust gas temperature gauges etc. However, when I bought MYRO, the carb heat and fuel pump wiring had been removed to go on MZEL, the complete battery side with accessories and wiring had been removed for the same reason and other bits and pieces were either missing or had had wires cut.
That wasn’t a problem, I knew about those things and they were all part of the deal when I bought MYRO. So that’s why when I bought the engine off Mark at Galaxy we took great care to preserve MYME’s wiring loom as far as possible so I could have that along with MYME’s panel and the instruments and gauges it still contained. It meant in effect that MYME’s wiring, instruments and gauges would become MYRO’s and the only problem was that although I was there when many key items were disconnected, for several (notably engine related equipment and accessories) I hadn’t been. And there’s no such thing as an AX3 wiring diagram!
So I’ve had to find and work things out for myself. This was the ‘inventory’, so to speak.
MYRO’s panel still contained a slip ball, airspeed indicator, altimeter, vertical speed indicator, RPM gauge and a dual CHT gauge, still connected. It also had the starter switch still in place and connected but no master switch cabling and although the fuel pump wiring had been removed, there was still a useable fuse holder for it. The dual EGT gauge had been removed and the connections for both temperature gauges had been cut at the engine end.
MYME’s panel came with a complete wiring loom except some connections had been broken by handling. There was the odd anomaly – for example, MYME had a fuel pump with a fuse but apparently no switch to operate it! Also, Mark had removed both temperature gauges but their connections were still in place so based on how MYRO’s dual CHT gauge was connected up, it wouldn’t be difficult to drop two replacements in. MYME’s panel contained a fuel pressure gauge, RPM gauge, a slip ball, airspeed indicator, engine hour meter and a master switch with fuse and wiring.
So my problem was to fill MYME’s instrument panel and successfully connect up all the necessary wiring, to go in MYRO. To do so I had had to buy a new dual EGT gauge to match MYRO’s existing dual CHT one and as MYME’s fuel pressure gauge showed signs of a slight but very oily, dirty leakage and was also stuck at just over 0.2 Bar, I thought it better to replace that with a new gauge as well to save possible future problems.
I worked out that MYRO’s master switch as it had been wired apparently only controlled the accessories – the main 12V live lead was connected straight to the starter switch before then jumping over onto the main fuse holder to which the accessories as far as I could see (as most had already been removed) had been connected. This meant that with the master switch off, you could still start the engine, which I did not like one bit even though it would still need the key to do so. The Rotax 503 wiring diagram does not show any form of master switch so I had to devise my own wiring set up. This has the main 12V supply connecting to one side of the master switch and the other side to the main fuse holder. The other side of the main fuse then connects to the starter circuit on the starter switch which then connects to the starter solenoid. So the starter cannot be activated even with the key in unless the master switch is turned on. A connection is also taken from the switched side of the master switch to the fuel pump switch. This in turn then activates the fuel pump via it’s own fuse.
I’m very happy with the results. I don’t have the faintest idea how this part of MYME’s wiring was done – I’m pretty sure it wasn’t exactly as I’ve done it – but hopefully it will all work as I intend without any future problems. I’ve also tidied up a lot of rather poor connections by removing some pretty awful connectors and making soldered joints enclosed in heat shrink sleeve. This considerably improves both appearance and quality and I believe should lead to good future reliability. I still have a bit more to do in that area as well.
As usual, the job started with ‘repairs’. When I stripped MYME’s panel I found that the RPM gauge it contained was a total bodge being held in place by a thick black goo even though there were some screws in place. So it had to be chucked and MYRO’s one used instead. Trouble was MYRO’s RPM gauge didn’t need holes. The same went for the temperature gauges. The ones that had been removed were screw fit whereas mine were not, so the holes that remained needed to be repaired. The fibreglassing bit of the job was a doddle – the problem was colouring the filler used to match the rest of the panel. I didn’t expect to be able to make the holes invisible but I also didn’t want them to stick out too much like a sore thumb. In the end I managed to get a reasonable colour match by mixing grey and white car paint with a trace of blue emulsion that I had in the garage but unfortunately try as I might I could not get the paint to shine. Oh well, I don’t think I’ll notice that too much when I’m actually flying MYRO 😕
I’ve not finished the whole panel yet but at least I’ve done all the electrical work. Here are a few pics to finish off showing where I’ve got to. First, a general view of the back of the panel.
On the whole I’m very pleased with it so far because I’m a great believer in the old maxim ‘if it looks right, it is right’. Now the backs of the hour meter and temperature gauges.
The connections on the back of the new dual EGT gauge in the centre aren’t up to scratch, unlike those on the dual CHT gauge on the right, so I still have to redo those. The hour meter on the left has a reading of over 5000 hours on it, considerably more than MYRO’s 2000 or so. It doesn’t really matter because the gauge is only used to calculate the figures for the log books but I may replace it, I don’t know. I couldn’t use MYRO’s old hour meter because it was the wrong shape. Next, here’s the wiring for the master switch, main fuse and starter switch. I’m very pleased with it – I think it’s quite neat 😉
The same goes for the next shot which shows the backs of the RPM and fuel pressure gauge and the wiring for the fuel pump switch and fuse.
The original RPM gauge connections that I replaced were awful, to put it mildly 🙂
Finally, a shot from the front of the panel. You can see the repairs I mentioned earlier, four little blobs around the RPM gauge and each of the temperature gauges.
The fuel pump switch is over on the left with its fuse next to it. The master switch is to the left of the starter with a neon that I hope will illuminate as soon as the master is switched on above it. I haven’t been able to test that yet. The main fuse is to the right of the starter.
Rotax specify that a 16A fuse is inserted in the line between the voltage regulator and the battery. There is one in the wiring I’ve taken from MYME but if I’m not mistaken, it’s in the wrong place! That’s a job for next time I think.