Tacho killing engine when signal connected

[Pat S67]

Hi Guys,

I picked up a cluster from a 2001 M900 Carb'd to refit to a 1995 M400, checked through the wiring diagrams, and apart from a few of the idiot lights not supported, supplying a ground to the Neutral light, and adding the "Signal" through the J pin of the pig tail instead of the side stand switch, all was going well.

Problem: As soon as the signal (tapped from the middle connector on the right igniter) is connected the engine starts firing on only one cylinder, and will die shortly after. I tested the tacho on my 2001 M600 (came standard with a tacho) and it behaves exactly the same. First assumption is the "new" tacho is a dud.

Would a failed tacho do this, or is this tacho simply not suitable for the M400/M600



Rear of the M900 tacho



Front of the M900 tacho



Rear of the working tacho from the M600



Label on the working tacho from the M600 there's nothing on the M900 tach except for a brown dot sticker if that is significant.



Point where I am taking the tacho signal from (centre connector)

TIA Pat

[Speeddog]

A 2001 M900 would be injected, not carbureted.

Possibly the tacho is different on the injected bikes.

[Pat S67]

Thanks speeddog, could well be different. Checked the listing from the seller, they only quoted it as being from a 2001 M900.

[Pat S67]

Found a generic 2001 monster manual, and sure enough there is 2 wiring diagrams, one for injected and one for carb'd.
The injected diagram shows the tacho signal coming direct from pin 3 on the ECU.