I have had the ARP ice detection system, model 107AP-12, installed in my Musketeer with the Lycoming O-320 E2C naturally aspirated engine since about 1990. Recently the detector stopped working and the problem was where the three conductors feed into the end of the probe. Vibration had worked off the conductor insulation and hence signal was not getting either in or out of the probe. I ordered a new probe which appears to be pretty much the same as the removed probe with the addition of a black dot painted on the body of the probe. Fortunately, there are instructions included with the probe and they should be read before removing the old probe. In brief, the throttle has to be set full open, (throttle valve wide), so that when you remove the old probe and install the new one, that the throttle plate does not run into the portion of the probe that sticks into the throttle barrel – appears to be an electric eye that senses ice buildup – sure works well, regardless. The painted black dot on the external body portion is so that one properly orients the internal portion of the probe. The black dot faces the carb air inlet, (down in the case of my Marvel Schebler MA-4SPA). To facilitate the proper orientation of the dot, one has to insert one or two thin shim washers and a lock washer prior to threading in the probe. I felt that ARP should have included suitable washers as that sort of minor item can be a showstopper plus a nuisance to source if one does not already have suitable washers in stock. The three conductors off the probe are terminated with nominal ¼” spade crimp connectors, (2 female and one male). While suitable 0.025” ends are pretty easy to find, I thought that they may as well be included with the probe, along with the thin washers – in other words, a full meal deal- that would have got five stars. I recommend the ARP optical system for ice detection. The best time to install same is when is getting your carburetor overhauled. This is because the hole in the carb body that the probe threads into is usually filled with lead. The best time to drill out the lead is during an overhaul – also the threads usually have to be tapped in. The head end is relatively easy to install on the panel. I used a 3” instrument hole. Re wiring, it requires a hot off the main buss and a ground plus three conductors thru the firewall out to the probe.