trying to put a tach on a 78 merc 70hp

[halfor]

I was ohm-ing out some wires and 2 of them just fell apart, crumbled in my fingers, guess being a 78 has its issues, any way I'm wondering if the signal wire on the tach (brown) should be grounded, I was assumed it was a open closed type of signal from a positive type terminal but now i have to ask anyone if it is a negative signal and the fact it shorts to ground is what it should be doing???

 

[Bob_VT]

Re: trying to put a tach on a 78 merc 70hp

Historically the older Merc's had wires that just fell apart after years of use. Do not stop there....... start inspecting and replacing ALL the bad wires with high quality marine grade tinned wired