I need to replace the tachometer on the boat. The gauges are Stuart Warner and I'm going to replace all 4 of them. I have a question for the board. How do you hook up a 'Hall Effect' tach?

The tachometer on the boat is electric and driven from the alternator. There's a problem with supply on a replacement from SW but there are SW tachometers using the 'Hall Effect' drive. I have no idea what it takes to set it up if I don't use the alternator drive tach. Seems that it's probably easier to just wait the month for the correct one to arrive but then again,,, getting a 'hall effect' drive might be an easy setup along with being better way to hook it up. Right now the tach is intermittent and when it stops working correctly some part of the system causes havoc with the auto pilot sending the boat off course.

I motor at 1,600 rpm. The tach shows 1,600 for a while and then slowly drops to about 800. If I shut off the power to the gauges and flip the switch back a few times it pops back up and is normal again for about 10 minutes and then drops. Don't think it's the alternator but the tach as the amp charge rate remains the same when it happens.

Anyone have experience on this issue? Perhaps taking the tachometer out of the charge loop would be a good thing.