Tachometer help

[WildBill79]

I can usually use the search buttom and get enough information about what I am doing without having to post a message but this time I am stuck. I have an 1986 Bayliner Capri with an 1986 85hp Force. The motor runs great and has never gave me any trouble. My boat didn't come with a tachometer so I decided to add one. I bought a 20 pole tachometer, wired the purple wire to the signal post, power to power, and ground to ground. When I turn the key, the tach moves to 0 but does not given me any reading when the motor is running. It just stays at 0. I checked the wiring at the motor and everything seems to be fine. Could the rectifier cause this? I also installed a volt gauge and when the motor is running it takes a while for the gauge to show 14 volts. It will stay at 12 for a while then eventually start creaping up. I checked the grounds on the motor and all seems well. Any idea?

Bill

 

[Frank Acampora]

Re: Tachometer help

When the ignition switch is turned on, the tach is not getting a signal because the engine is not running and it SHOULD zero. This is correct.

Normally, you wouldn't expect the rectifier to affect the tach because the purple wire is attached to one of the A/C terminals and reads A/C from the stator before the rectifier.

However, I seem to remember having trouble with a 20 pole tach reading improperly AND when I changed the rectifier for a different reason, the problem went away. SO: it is possible that your rectifier is causing the tach not to read at all.

See if you can get the cheap rectifier (square) from Radio Shack. If it doesn't solve the problem, you are not out a lot of money. If it does, you're gold.

 

[hgmatt]

Re: Tachometer help

Frank,
If one were looking for a rectifier at Radio Shack, what would one look for? I for one, decided that I would run my motor sans the battery hooked up (pulled the bat. cable while running the motor/rookie mistake). If I remember correctly, this usually fries the rectifier. I'm still awaiting the starter, but I wanted to take a look at/research possibilities.

Matt

 

[WildBill79]

Re: Tachometer help

I guess I should clarify. When the motor is running the gauge will read zero. If I turn the motor off and remove power from the gauge it will drop below zero. I am also crurious about which rectifier to get from Radio Shack.

 

[Frank Acampora]

Re: Tachometer help

Sounds like the tach is not getting signal. A shorted rectifier might do that.

I don't know the Radio Shack number--someone on this forum does though-- But if you ask for the square one with a capacity of 20 amps they will probably know. BTW: the alternator only delivers 7-10 amps max.

 

[WildBill79]

Re: Tachometer help

Is there any way to view the signal with a meter to determine if the tach is bad?

 

[Frank Acampora]

Re: Tachometer help

Can't help you there.