I am having a problem with the tach on my recently acquired used boat. It reads backwards. When I start the motor the tach reads just below 0 RPM and when I increase throttle it decreases with the change in speed of the motor When I let off the throttle it moves back to 0 RPM. It's working in reverse.<br /><br />Motor: 50 HP Merc 4 cyl electric start (1981)<br /><br />The boat is a 1988 and the tach looks like an original installation. The tach is wired to the side mount Mercury engine controls. The tach has 3 terminals - 12V, ground and sender.<br /><br />Here's what I have checked so far:<br /><br />1. rectifier and stator check out OK. I followed the procedure in the shop manual. <br />2. Battery voltage - 13 volts with motor off<br />3. Battery voltage - 15 volts with motor idling.<br />4. Continuity from gray wire on post C of rectifier to sender terminal on the tach.<br />5. 15 volts across the 12V and ground terminals of the tach with motor running.<br />6. 7.5 volts between 12V and sender terminals of the tach with motor running.<br />7. 7.5 volts between the sender and ground terminals of the tach with motor running. <br />8. The light in the tach is wired between the 12V and ground terminals and it lights when the motor is running.<br /><br />I am checking voltages with an analog V0M.<br /><br />My conclusion at this stage is that the tachometer is bad. It appears that the<br />tach is getting a signal - but the needle is moving the wrong way. <br /><br />Does anyone have any suggestions/opinions before I spend the $$ to see if I am right? <br /><br />It doesn't quite add up to me.<br /><br />Thanks in advance,<br />Russell McPherson
