67' Merc 650 Tach issue

[suttonj]

I recently purchased an old boat with a nice 67' Mercury 650. The seller gave me a tach but told me he could never get it to work.<br /><br />Looking through the forums I descovered that there is a tach plug/jack at the front of the MerControl, and I believe I know the correct terminals for that plug.<br /><br />Trouble is I don't think the tach that he gave me works. It is an old SUN Tach.<br /><br />I wanted to buy a newer tach, but I don't know how many stator poles my alternator has. From reading the forums I'm guessing 12, but I can't find anything concrete for a motor that is nearly 40 years old.<br /><br />What kind of signal should I have at the tack jack on the front of the MerControl? Is it just DC voltage that changes with the RPM?<br /><br />Thanks for any advice?

 

[Laddies]

Re: 67' Merc 650 Tach issue

Its 12 pole 6 pulse you willn have to move the tach sender wire to the rectifier

 

[suttonj]

Re: 67' Merc 650 Tach issue

The Rectifier has two wires from the "Alternator flywheel" and one (RED) that goes to the "Switch Box Assembly". I assume it goes to one of the two directly from the alternator, correct?<br /><br />The Old Sun Tach says it is for 4 cyl 2 Cyl. I'm wondering if it is not the type that should be connected to the alternator.

 

[Laddies]

Re: 67' Merc 650 Tach issue

The sun tach goes to the mag but a new style goes to either yellow on the rectifier