Tachometer Install

[clemente_v]

I just made a new dash and installed new gauges. I have a Trophy CC1703 Mercury 90 four stroke. I’m at this point don’t understand why the tach is not reading. The sending wire is good and I tested it with a multimeter set to AC. The meter response to the change in the motor’s RPM. I discovered when I connected the tach with the multimeter still connected to the tach wire from the engine, the tach works. The multimeter is connected to ground and the positive to the tach wire from the engine.
The tach is wired to power and to ground. All the gauges are sharing power and ground. I’m baffled at this point how the tach is working with the multimeter connected. How do I bypass the multimeter. Connecting the tach to the tach wire is not working. Please advise on what to do.

 

[alldodge]

Welcome
Is the gauge and motor original?

Reason for the question is if Tach is designed for a 2 stroke stater and not a 4 stroke

 

[clemente_v]

No it’s a replacement. It’s for a four stroke. There is a tach module in the engine. I don’t understand why it has that or the purpose for it? The tach wire was connected to it. I also replaced the module with a new one. Tested the current from the module. It read 1 volt. The wire coming from the voltage rectifier was 12volt. I by bypassed the module and I have the tach reading now. I left the module connected to the other 2 wires black and purple.

 

[dingbat]

No it’s a replacement. It’s for a four stroke. There is a tach module in the engine. I don’t understand why it has that or the purpose for it?

You don’t say which motor, but if it’s a fuel injected engine the “tach module” is an induction sensor. Replaces the functionality of a distributor in the timing of the motor.

 

[Dukedog]

tha gray goes ta tach signal post..
blue is tha light for tach...
purple is switched power for gauge
black is ground

 

[clemente_v]

You don’t say which motor, but if it’s a fuel injected engine the “tach module” is an induction sensor. Replaces the functionality of a distributor in the timing of the motor.

Sorry it’s a 2005 Mercury 90 hp 4 stroke.

 

[QBhoy]

You have the wires mixed up, I’d think. The meter is finding a path to ground or earth for it. See one of the posts above about wire colours and you’ll be right.

 

[clemente_v]

Tach is working now. See previous post.