brlawson Posted October 1, 2016 Share Posted October 1, 2016 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? Link to comment Share on other sites More sharing options...
Meinolf Posted October 1, 2016 Share Posted October 1, 2016 Hi, the tach is driven by a square wave signal from the ECU, pin3 on the 15M & RC. Cheers Meinolf Link to comment Share on other sites More sharing options...
stewgnu Posted October 1, 2016 Share Posted October 1, 2016 Did you open the unit up at all? Link to comment Share on other sites More sharing options...
brlawson Posted October 1, 2016 Author Share Posted October 1, 2016 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. Link to comment Share on other sites More sharing options...
docc Posted October 1, 2016 Share Posted October 1, 2016 Tach also gets power through the first two relays. Are all other systems *go* (headlamps, brakelight, horn, warning lights)? Link to comment Share on other sites More sharing options...
Kiwi_Roy Posted October 3, 2016 Share Posted October 3, 2016 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! Link to comment Share on other sites More sharing options...
stewgnu Posted October 3, 2016 Share Posted October 3, 2016 I'd open the units up- when my old ones went, and i opened them up, i found broken wires inside. Link to comment Share on other sites More sharing options...
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