I have a MTD lawn tractor with a Briggs and Stratton 18 hp twin II engine. I'm not getting any spark to the plugs. I know there are safety switches but I don't know where they are at. I know there is supposed to be one at the seat and one at the brake but I don't know where. This is approx 2002 tractor - 42" cut, B&S model number 42A707. Thanks for any help in advance!