50 horse johnson tach problems

[greasemonkeyjmj]

i have a 74 jonson 50 horse i installed a tach and cannot get it to work. i wired the sender wire to the grey wire in my remote box. wired my ignition wire into my keyswitch. i am getting fire to the ignition post on the tach, and i have a good ground. with the key off the needle sits at 2k. when i turn on the key it falls back to zero, but when i start the engine it doesnt move. i have been told my engine is a 12 pole 6 pulse engine, so that is what i have it set on. any info would be greatly appreciated

 

[HighTrim]

Re: 50 horse johnson tach problems

First off, did you disconnect the battery before making any connections?

You stated you had 12V power, but do you have a proper ground on the tach?

If you have a proper ground and power, next check the signal source. The signal is a pulse-positive output that?s provided directly from the stator assembly through the rectifier. A peak-reading voltmeter set to ?positive? and the lowest volt scale will enable you to read any voltage output (on this circuit) from the stator. You could try running a test lead directly from the motor to the SEND terminal on the gauge.

Short of that, you may have blown your rectifier. Check your manual for the testing procedure, or check the FAQ here on iboats for a thread by Joe Reeves.

 

[ezeke]

Re: 50 horse johnson tach problems

Your rectifier may be partially bad. Try switching the gray wire from one yellow wire to the other on the terminal block at the engine.

If your voltmeter doesn't show a change at the battery terminals when you go from off to run, the rectifier may be shot.

 

[greasemonkeyjmj]

Re: 50 horse johnson tach problems

i did not have my battery disconnected when i wired the tach. to be honest i didnt think to unhook it.i know my ground is good, because i clipped my test light to the ground post on the tach to chech for power. and i am getting 12v to the ign post on the tach. and on the tester, the oly thing i have is just a plain digital ohm/volt meter.but if i had a bad rectifier, would it still be showing i am getting a charge to my batteries ?

 

[greasemonkeyjmj]

Re: 50 horse johnson tach problems

i will try changing wires on my rectifier, but first i am going to bypass the wiring harness and run a jumper to the tach from myrectifier i can start motor and hook my volt meter to the battery and watch the voltage change with the change in rpm on the motor

 

[greasemonkeyjmj]

Re: 50 horse johnson tach problems

ok i was checking the wires from my rectifier, i checked my gray wire that i wired into in my remote, and on one side of my wiring harness plug, i have continuity, but at the other side i do not, so i pulled the plug apart and on the remote side of the plug there is no contact in the plug to match up with my grey wire on my motor side of the plug. on the motor side the grey wire sits near the outside in the plug, but on the remote side the grey wire is very near the middle.

 

[ezeke]

Re: 50 horse johnson tach problems

In the OMC wiring world, the gray wire is the sender for the tachometer, so it must have continuity from the engine's terminal block to the tachometer.

 

[greasemonkeyjmj]

Re: 50 horse johnson tach problems

o.k i went ahead and ran me a wire from the terminal block on the engine across to the remote side of the main power plug and the tach works. i am not sure if it is reading correctly, it seems to me like it may be reading a bit high. it has a synchronize screw on the back, but with out knowing what the actual rpm is, i dont think i want to mess with it. THANKS TO EVERYONE WHO OFFERED IDEAS ON SOLVING MY PROBLEM