I don't know if this is useful or not, but I seem to remember that some channels on that RX are for high speed servos unless you change the setting. I know that a standard servo plugged into the Orange 2.4 receiver from hongkong will get fried if the receiver is not set for slow speed servor. Iwould think the kill switch and tachwould look like a slow speed standard servo. This may not apply at all, but then again, it might.

What ignition and receiver battery voltage are you using. I also seem to remember that the Rxcell didn't like 6V. Again maybe nothing to do but agan maybe.

It does sound like you may have some voltage on the ground. Maybe a chafed lead to the pickup?
Don