The black wire on a Briggs is the ignition kill wire: its only purpose is to stop the engine. If that is the only wire your engine has, it has no electric starter, and no generator or alternator. Your Tecumseh will have a kill wire too, it is usually dark green. If it also has a yellow wire, it is usually the AC output from an alternator. A red wire is usualy the DC output from a rectifier connected to the alternator. Neither the yellow nor the red wire is any use to you unless you have a battery on your mower. If your Briggs had no generator, it sounds as if your mower is pull-start only, with no battery. If that is the case you will not be using either the red or yellow wire, you will just be using the dark green wire in the same way you previously used the black wire on the Briggs. Incidentally if you have a dark green kill wire, grounding it will prevent your engine from firing whenever it is grounded.
