Yamaha 6Y5 Tachs going Haywire

[eelpoint]

I'm as confused as you. I'm honestly baffled, because I know these motors fairly well as I have another set on another boat. I know the electrical systems are top notch and rarely fail.

[panasonic]

Something has to be in common with both tachs for them both of them to being doing exactly thing. So the question is what is do both tachs have in common? That is what I would look for.

[eelpoint]

Trying to upload a video but server won’t let me.

[boscoe99]

Have you had any lightning strikes in the area?

[boscoe99]

I've done similar with Eric from GaugeSaver. We started with one connection (yellow) to one tach, then tested by turning key switch to corresponding motor on. If we were successful we then went to green then test, black then test, blue then test, We then connected the Fuel Management and Speed gauge (similar procedure) Yellow then test , Black then test, Blue then test, Red then test, Green then test, Green/white then test. We then moved onto the Port Tach and connected that separate from Starboard Tach, Fuel Management and Speed Gauge... all tested good. Then we moved to the 4-pin connectors and as soon as we connected the Orange, Black, Grey 4 pin connector (not the Pink wire according to the label) gauges went into cardiac arrest. I can try this test in the reverse method as you suggest, would expect same results No?

How about disconnecting the Orange, Black, Grey four pin connector on the motor side and see what happens.

One motor only please.

[eelpoint]

This is a great idea. This is what makes this forum great. I will try in the morning and report back

[eelpoint]

Well I qualify for ******* of the month! On engine side I was blue to Ivory on one of the connectors. Stupid stupid man I am. I appreciate all the comments. Thank you all!!

[eelpoint]

Enjoy your weekend !

[boscoe99]

Thanks for the feedback. Glad you fixed your problem.

I am still not understanding how your tachometers did what they did but so be it.

The more I know the less I understand.

[99yam40]

is there a chance the wrong plug was hooked in

dang it looks like I guessed right

and I am at a loss on how that would affect both tachs