I got a 1974 Mercury 500 thunder bolt with lightning energizer ignition and I was just wondering what part this is in the picture I have attached and circled in green. I just finished rewiring the internal engine harness so that I can attach any tach I want using the rectifier wire. And I noticed that this wire to this mercury switch was all coroded. Is this mercury switch the engine kill or does it have something to do with the tachometer? Do I need to have it on? Any help would be great thanks.

