Looking for a didgital,lighted tach for spark plug wire install. My 76 merc 500 thunderbolt has a floating ground and after market tachs will not work they tell me. Please help
Tried that, said they would not work with floating ground thats why I am looking for one that will go to the plug wire . They have them but none I have found are lighted.
if you don't mind me asking, who told you your motor has a floating ground? The battery is connected to the motor so the motor is grounded to the battery. Any accessories are connected to the battery, so the ground is common to the motor and accessories. You do have a charging system, don't you?
Oh, I get it. It's for a boat, of course it has a floating ground.
Go to a gauge website like faria or teleflex. They will have information on which tach's will work and how to hook it up. I'm not sure about digital but they will have analog for sure. There's only a few connections, ign which is +12, ground which is -12 or neg, and sender which is a gray or brown/tan wire AC tach signal from the stator. Oh yeah, and the instrument light connected to the nav lights or the ign, your choice. Really don't understand the "floating" ground issue unless it has something to do with digital instruments.
I've got one of these on my '76 OMC 55 HP, works fine. There is a cheaper knock off version on ebay too, I've use them but they don't hold up as well as the Tiny Tach.
My tach has brown wire to rectifier,black to ground,white 12v ign, 6 pole setting. Has new stator,rectifier. Old tach does not work and new tach does not work. Guess I will start checking for breaks in the wire.
