How to troubleshoot non-working Tach.....

[bluemarshboater]

Not exactly sure how to properly troubleshoot my tach....... I have a 5.0 mercruiser (1992) in a Bayliner capri. I have some links to pictures of the wiring, etc.. Using a test light while the ignition is on I get power to two of the three wires in the tach plug (see picture). I get power to the white and purple wires, so I'm assuming the black is a ground. How do I isolate and test for dead tach, bad wiring, or etc..?

http://idisk.mac.com/videopuppy/Public/tach1.jpg
http://idisk.mac.com/videopuppy/Public/tach2.jpg
http://idisk.mac.com/videopuppy/Public/tach3.jpg
http://idisk.mac.com/videopuppy/Public/tach4.jpg

Thanks
Dave

 

[Bifflefan]

Re: How to troubleshoot non-working Tach.....

Ive never had to test for this but,
id think by process of elimination it can be done.
if you have power where you should, and ground where you should, and the wire going to the coil (triger) is good (continuity wise), then the only thing left is the tach is bad.

 

[bluemarshboater]

Re: How to troubleshoot non-working Tach.....

Agreed, so I guess I can send some power from the tach wires (at the tach it self) back to the coil to see if the wires are connected and have continuity.

Where would the wires be..... one on the tach, and the rest?

Would anything be at risk by sending some power back that way..... 12v? Guess I should just disconnect the wires for this.

Best
Dave

 

[Bifflefan]

Re: How to troubleshoot non-working Tach.....

id use a volt/ohm meter. you can find one at harbor freight for about 10 bucks or at napa for a little more. the one from napa will be better quality. and they really come in handy.
then you can ohm check the wires to the coil. you can the voltage thing too but its harder as you have to discontect the wires first.

4 wires is all you need to make it work
1 power 12v+
2 power for the light 12v+
3 trigger from - side of coil
4 ground
more than that and ???

 

[bluemarshboater]

Re: How to troubleshoot non-working Tach.....

I have a good voltmeter. I give that a shot, just have to brush up on how to use it for that purpose.

Thanks

 

[bigskiohio]

Re: How to troubleshoot non-working Tach.....

my tach didnt work 35yr old boat so ithought it was junk. i was bored and cleaned all my connections and everthing works now.Mine was the screws in back were not touching inside of tach as a washer was holding it away. but the other ones were just corroded.