Tach stopped working, what to check?

[chrisg]

I have a ?99 merc 60hp bigfoot (2-cycle) and just noticed that the tach has stopped working. This is on a 24-foot pontoon, and I just had the motor put on the boat end of year. I checked the wires going to the Gauge. It has 12V and the Gray wire goes into the wire harness. What should I be measuring on this gray wire? When I measured with a DC voltmeter, it was all over the place. I opened the motor and did not see anything loose inside. (The wire harness goes into a plug at the back of the motor.). Also, when I first start the motor (starter running) you can see the needle moving, but then once the motor is running, the needle is at 0. I also noticed there is a gauge on the dash with PSI marked on it and that moves as the RPM increase. What would that be measuring? (I was going to replace that gauge with a gas gauge).

What should I check first? This did work, and I don?t know when it stopped working. I am going to take it to the marina next week, but thought perhaps someone can tell me what to check. IE some connector inside the motor has wiggled loose.


Any advice would be helpful before I send it to the shop.

 

[sschefer]

Re: Tach stopped working, what to check?

The PSI is your water pressure gauge. An increase in RPM should make this rise so that's o.k. By the way, that guage can save you an engine so do not remove it. Put a gas gauge somewhere else.

What you are describing, if all the wires are tight, is typical of a failing voltage rectifier/regulator if your engine is so equipped. However, it could also just be a bad ground. FYI, the 12v + on the gauge is for lighting only, it has nothing to do with the operation of the gauge.. usually... We don' know what motor you have.

I'd bet on the Voltage regulator.

 

[chrisg]

Re: Tach stopped working, what to check?

thank, As I stated, its a '99 merc 60hp bigfoot. now I know what the PSI meter is for, I will watch that one periodically. And I did re-do the ground wiring on the boat, running a new wire from the battery to the radio, and I connected all the grounds together. ( perhaps I disconnected the tach's ground?) I will check how good the ground is on the meter next time.

 

[sschefer]

Re: Tach stopped working, what to check?

thank, As I stated, its a '99 merc 60hp bigfoot. now I know what the PSI meter is for, I will watch that one periodically. And I did re-do the ground wiring on the boat, running a new wire from the battery to the radio, and I connected all the grounds together. ( perhaps I disconnected the tach's ground?) I will check how good the ground is on the meter next time.

Well here's what I know for sure via been there done that... If you accidently put positive to ground by doing something like accidently switching negative and positive on the battery, you will blow the recitifer/regulator. Believe it or not this is by design. It is supposed to protect the more costly switch boxes. I knew mine was toast when it would not work then suddenly start working and then sometimes hang way up or just go dead. Weird symptoms but it was the regulator/rectifier that was blown.

 

[jasona]

Re: Tach stopped working, what to check?

i would agree the best place to start is to test your rectifier. my tack stopped working on boat with a 1989 80hp merc, and the simple test comfirmed it was my rectifier.
i'd suggest you get a service manual for your motor and an ohmmeter, the test takes all of two minutes, and you do not need to remove it from the motor.

 

[chrisg]

Re: Tach stopped working, what to check?

So, this rectifier, does it impact the charging system? If so, should I notice that when the motor is running, the voltmeter gauge does not increase as RPMs go up? Or is this only for the tachometer? (IE is there something else I can observe to indicate that the rectifier is the issue?)

OK, I'm on www.crowleymarine.com, and have not found this rectifier, where is it located?

 

[chrisg]

Re: Tach stopped working, what to check?

Its been verified, the tach stopped working! Why would a tach just go out?

Gee they are expensive ( compared to the other gauges!)

Well, I will worry about it in the spring.