Tach wiring help...attached pics

[Tinlizzy]

Greetings,
I also posted this in the electrics forum, I am not sure where to post
I am in need of a bit of help..I am in the process of identifying wires/rewiring on the boat. The owner before me seems to have a bit of a mess here with wires. I am onto the tach wires and trying to figure these out. I have attached photos. This is for a 1971 115 hp inline merc.

First pic: Is a shot of the switch box assembly on the distributor side. The second terminal down from the top has two wires, a white and a red. The red wire was added to run from the motor to the ground terminal on the tach. The white attaches to the distributor.

Second pic: This shows the red wire running out of the engine to the tach.

Third pic: This shows the back side of the tach. The black wire coming off of the back is spliced to the red wire, for the ground.

The question is, why do I need this red wire grounded from the side of the switch box assembly and not a common ground from the battery? Does this tach require this from the distrib? thanks in advance!

 

[Chris1956]

Re: Tach wiring help...attached pics

Tin, It sounds like the wiring is messed up. If the tach is a '71 quicksilver, then the tach signal MAY come off the switchbox. Specifically the brown switchbox terminal on the starboard side of the motor. If the tach is a universal or newer tach, then the tach signal comes off the rectifier AC pole (either one). In both cases the tach should get +12v and ground from the battery as well.

You should be careful with the wiring. You do not want to blow out the swithbox or distrib trigger.

 

[burroak]

Re: Tach wiring help...attached pics

There sure is a lot red wire in this boat. I don't have the engine side of the wiring harness, but this may help you clean up the rest:http://www.stingrayboats.com/products/pdf/wiring/240CS_dc_wiring_dual_battery.pdf
http://i180.photobucket.com/albums/x54/burroak1/X1100tmp.jpg

 

[Tinlizzy]

Re: Tach wiring help...attached pics

Thanks for the replies

Chris,
The brown wire is the sending wire for the Tach I am positive. I am just not sure why they are running that ground wire all they way back to the motor and the side of the switch box?

I do not want to blow the switch box. The rear of the controls has three wires coming out brown/black/white. These are for the tach, but they did not use the black for the ground. When I tested the ground it worked on the meter for 12 volts, so should I try to disconnect it from the motor and use that ground and see what happens?

 

[Chris1956]

Re: Tach wiring help...attached pics

Tin, The black wire in the MerControl should be ground. You should try to find out where it is misconnected. It should run to the negative side of the starter solenoid on the motor, as well. Make sure the tach signal is connected to one of the AC terminals on the rectifier. The older mercs connected that wire to the switchbox, which doesn't work for the newer universal tachs.