I was having noise in the SL40 comm radio on my RV-12. After a lot of troubleshooting I decided to replace the spark plug caps. I had a suspicion that the 5-ohm ceramic resistor may have been damaged from pulling (manhandling) the rubber caps when removing the plug wires. The rubber cap is easily deformed.
I purchased new NGK Spark Plug Resistor Cover – 90 deg Elbow Type LB05F on eBay for $49.68 for qty (8). These caps are rigid phenolic and should prevent future damage to the internal 5- ohm resistor. Installation is very simple – just unscrew old cap from wire end and screw on new cap.
Radio noise problem is now fixed…
Hinckley, Ohio (1OA2)
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
RV-12 E-LSA #120058 AWC July 2012 N633CM
RV-12 Bought Flying Oct 2015 with 48TT - Hobbs now 490
LSRM-A Certificate 2016
Special Thanks... EJ Trucks - Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - 1st Lt. Captain B-17H