I found a thread where this was touched on. Looking for more details so I do this right... I have a '62 Merc 500 and an Air Guide 865 tach. Tach has a positive and negative terminal. So negative goes to any ground to he battery? Positive goes to where? Last project I hooked it up to the key switch, "M". Easy as it was in the dash and works great. This key switch is in the control unit. Do I need to go in through the screw pictured or do I run a wire all the way to the engine? If to the engine how should I bring it in the housing and then to what screw or connection? 4 pics of what I have. Has anyone done this? Pictures? Please mark mine up or post a picture of yours or diagram.
Hi Dave, If you zoom in over the white label it is '865' in black ink could be a misprint... Here they show a 870 (picture) and no 865. So I run a two lead wire all the way back following the control harness and into the housing best way possible? Guess I could try to trade for a 658 if it doesn't work.
I might be in the market for a tach for my '77 merc 1150. It quit working at the end of last year. I did a little investigating this year but didn't find a problem. With the weather not cooperating this year I haven't had it in the water yet. Just wondering how available it will be and how hard a hit I am going to take. I would like to have a some what period correct one for my '59 Thompson - '77 Merc combo.