Thank you for all of the boat wiring expertise that you provide.
Here’s my issue:
I have a 2003 Signature Series Chaparral Model 280, with two 5.7 Liter Volvo Penta Gasoline Engines.
The dash mounted tachometer (see photo) needle(s) wander (drifts) around. I read that his could be caused by a bad ground. It could also be from poor signal connection.
Do you have any information on how the instrument is wired to the signal source. And what is the signal source?
On EFI engines, the tach signal comes from ECM. On carb engines, the signal comes from the distributor. Both use a gray wire and it runs through the boat’s engine harness, through the main engine connector, and up to your boat’s instrument panel. Some boat builders use a gray/red as the second engine tach signal to help reduce confusion. I would check all connection points of the gray tach signal wire for each engine.
Your best bet to help cure the drift, is to run a new, clean ground wire from the tachometer back to your ground bus or engine negative stud. You can remove the existing ground (black) wire on the back of your gauge and tie it up to prevent it from an accidental short.
Hope this helps,