Unknown tach wiring

[mrw28]

I have an old tach with my 1976 Merc 500. It was working last time it was used in the summer of 2003, but we didn't keep track of the correct wiring moving it from my dad's boat to my boat - it was removed from the old boat for us by a service center.<br /><br />The two wires from the bulb area (one white, one black) were attached to two of the terminals (possibly because that's where they used to be, possibly just for tidy transport), so I put the white input wire onto the same terminal as the white bulb wire, similar for the black wires, and put the third, signal, line onto the remaining terminal. I've been out on the water twice like this and there's no sign of life from the tach.<br /><br />My questions:<br />

• <br />
• Does anyone recognise this tach and know the correct way for me to wire this?<br />
• Will I have damaged the tach by using it wired like this?<br />

<br /><br />Here are some pictures:<br />

<br /><br />Thanks, Gubbins.

 

[OBJ]

Re: Unknown tach wiring

Welcome Gubbins!<br /><br />Can't see the one pic to well, but are there any letters at the indvidual posts on the back of the tach....Like "S" or "I"....maybe "G"?

 

[mrw28]

Re: Unknown tach wiring

Hi OBJ,<br /><br />Thanks for the welcome! Thanks for the advice too; The most obvious advice is the most valuable, and I can't excuse not looking for markings already!<br />

• <br />
• Top left: +12V<br />
• Top Right: AL<br />
• Bottom: GND<br />

<br />AL had better mean 'SignAL' then. So far so good, why isn't the tach displaying anything?<br /><br />I've put a multimeter across the +12 and Ground wires, I guess my next step is to use the multimeter across Ground and Signal with the engine running. Any other ideas?<br /><br />It'll probably be a week before I get down to the boat again - I'll post here when I have news.<br /><br />Thanks again, Gubbins.