Need better understanding of tach circuit

[brlawson]

Trying to get some guidance on all the components involved in the tachometer circuit in order to troubleshoot.

 

When I purchased the bike the tach was not working and from over the years of collecting Guzzi parts I happened to have a NOS tach and speedo so I just replaced it. Unfortunately, this did not work. I know the ground is good because the light works fine letting me know that even in the dark I can still see the tach is not working. 

 

Where to go from here...I assume the signal comes from the ignition. Coils? ECU?

[Meinolf]

Hi,

 

the tach is driven by a square wave signal from the ECU, pin3 on the 15M & RC.

 

Cheers

Meinolf

[stewgnu]

Did you open the unit up at all?

[brlawson]

Did you open the unit up at all?

Not yet, The one I have on there now came a NOS set of gauges. Neither the old or the new works which is what brought me here. Just want to make sure everything is as it should be before I crack the eggs open.

 

 

Hi,

 

the tach is driven by a square wave signal from the ECU, pin3 on the 15M & RC.

 

Cheers

Meinolf

 

Thanks, looks like a brown lead according to the diagram.

[docc]

Tach also gets power through the first two relays. Are all other systems *go* (headlamps, brakelight, horn, warning lights)?

[Kiwi_Roy]

As Docc says the red/black wire from the headlight relay provides power for the tach, the light is irrelivent.

 

 

Sent from my shoe phone!

[stewgnu]

I'd open the units up- when my old ones went, and i opened them up, i found broken wires inside.