I’m trying to help a guy who has a mercury 400 1970. I sold him a Airguide tachometer 667.
The Tachometer had a harness that connected to the front of his controller but causes the engine to die.
It was recommended that he purchase of sender module. Any assistance would be welcomed on how to connect the sender module and trace the correct wires to the controller. If there’s a short somewhere at least will know the components are correct. I’m posting a picture of the module that he purchased.