tach problems

[2ts]

i checked the voltage at the back of the tach it read 12.6, when i turn on the key the needle does not go to zero as it should, i got new tach and hooked it up just like the old one, turn on the key and it goes to zero as it should, start the baot and nothing it just stays on zero. so is it a bad connection on the motor where the grey wire hooks up to the motor.Also is there a way to check the old tach with it being out of the boat and not hooked up to anything, could i test it with a ohm meter ?

 

[2ts]

Re: tach problems

it is a 96 mercury 150 efi

 

[Silvertip]

Re: tach problems

There are only four wires on a tach. +12V when the key is on. Ground, Light, and Sense or pulse. I suspect you have a bad ground or you have some wires hooked up wrong. Use your ohm meter to check the ground wire. Red from meter to the ground wire (disconnected from meter). Should show continuity. If open, you have a bad ground. If continuity reconnect the wire. Measure +12V with the key on. Make sure the wire is on the corect terminal. If you have +12V = OK. If not, determine why. The problem is not the tach. Pulse - make sure it's connected to the "S" terminal on the tach. With the engine running measure the voltage (AC). You should see some meter movement on a low volts scale. Doesn't matter how much as long as there is some. If no reading, fix the pulse line from the engine or else the rectifier/regulator is bad. Does your charging system work? Battery voltage measures 13 volts or higher at 1500 RPM or so. If less than that it's not working and neither will the tach.

 

[2ts]

Re: tach problems

i have checked the voltage with the motor running and it checks out at 13.5 volts . is there any way to check the old tach that is out of the boat and not hooked up? i believe that i may have a bad ground or the gray wire is not hooked up tight enough?

 

[2ts]

Re: tach problems

also i had the shop for tune up and he schecked everthing out and said it was ok, i just forgot to tell him to fix the tach my fault on that one.

 

[Silvertip]

Re: tach problems

Yes, the tach needs a good ground and yes, the pulse/sender line needs a good connection. Check them!

 

[2ts]

Re: tach problems

i got home from work and took the cowling off the motor and found the regulators, and low and behold the gray wire was unplugged from the top regulator, someone had done this on purpose, plugged it in and started the motor it worked for a few seconds and then the needle went to zero. cut the motor off and got under the console and with nothing on except the battery hooked up there was 10.5 volts to the gray wire , 0 to the ign wire. cut the key on and the ign wire had 12.5 volts, and the gray wire still had 10.5 and i used the grount wire on the back of the tach to get these readings. so iam thinking the regulator is shot , the tach quit working an they unplugged it. any ideas any one ?

 

[2ts]

Re: tach problems

someone told me to hook the gray wire at the back of the boat to the other regulator and see if that works, i fit that makes the tach work i assume that the orther regulator would be bad?

 

[Laddies]

Re: tach problems

Yes, that would tell if one regulator was bad, heres some help from Teleflex as far as wiring etc.
http://ww2.tflx.com/obtachtrad.html