mercury 135 blackmax tach sig

[mr_plow]

hi guys

i own a ski boat which has a newly acquired mercury 135 blackmax. i originally had a merc 175 which went kaput.
when i swapped the motors over i found out that there were a few funny things going on with the wiring, firstly the main harness to both motors were the same but all the wiring was different. i couldnt get the 135 motor to turn over, so i swapped all the starter solenoids (which included the harness connection) from the 175 to the 135 and it started no problems.

when i used the 135 harness originally the tach and water psi gauge would illuminate with the key off which was a little weird, and now with the 175
harness on the 135 there is no illumination of the gauges at all and the tach and psi gauge have stopped working.

so rather than f around with the current loom i have decided to wire them directly to the motor for signal and power. power is no problem to tap, i will put a switch on the power wire to cut power so it can be switched off.

im really struggling to find where i can pick up the tach signal directly from the motor, as the manual diagrams only tell me the signal wire on the loom and not on the motor.

hope you gurus can help me out

[j_martin]

Black Max means big and black.

Many things change over the years, so year, or s/n is needed to help.

If they are both V6 carb's 2 cycle, or even EFI, the harness should have been plug and play.

[mr_plow]

yes very big, infact taking off the boat points to the sky with a front mounted fuel tank half full
my thoughts exactly, they are both v6 carb, basically identical apart from hp. the harness was a direct plug in, which is why i am thinking the original owner of the boat with the 175 had mucked around with the wires
im not sure on the year just yet, i will check the serial number but im pretty sure its a 1991

[j_martin]

Your best bet is to get the service manual with diagrams in it. It will have the control diagrams in it also. Put the whole shebang back to original and fun out without worries.

It sounds like the wiring is a little flaky anyway. Maybe the connector itself is dirty or worn and needs the pins spread a bit.

[mr_plow]

connecters seem to be fine, they have been cleaned with c02 contact cleaner, im not sure if im up to the job of re-wiring the whole harness..

i know the signal wire for the tach is grey, i have the grey on the upper tach harness but when i get to the main harness connecting to the boat there is no grey wire. all the wires on the tach harness seem to have no 12v constant, 12v ign or ground..

its got me stuffed whats going on here, in the manual it shows the main harness but the wires are not singled out in a diagram, its all one wire then it goes to the control box

[Chris1956]

Have you looked at the wiring diaghram at Maxrules.com? Grey is tach, Black/yellow is ign killer, red is Pos battery, Black is ground, Ign accessory (for gauges) is purple, choke is yellow/black, starter solenoid is yellow red. Overheat is tan

[mr_plow]

thanks for that link. this is the wiring diagram. would i be able to tap tach signal straight from the grey wire on the rectifier? also on the yellow/red wire off the starter solenoid would i be able to tap 12v ignition switch?

[Chris1956]

Yes. Grey wire should attach to rectifier. Tach signal is found there. You want purple wire for Ign accessory voltage.

BTW a '91 Merc will likely have dual voltage requlators, versus a rectifier.

[just york]

hey guys,
i just registered because of all the great info and advice i found on this sight. I am in the process of changing a perfectly good running johnson 88hp to a 91 black max 135, i pulled out of the woods. Between the mice chewing up the wiring and lack of proper storage it has been a handfull. I was able to splice wires back together and get it running, sounds like a really tight and powerfull motor. but i can not get the tach. to function. everything else works. the wiring harness from the remote to gauges was cut, through splicing and process of elimination i have the trim and trim gauge working, there is 12v at the purple, good ground and voltage that drastically drops and spikes at the gray and tan wires while engine is running. that would lead me to believe all signials are present foe a tach. to function but still nothing except a slight movement of needle when the purple wire makes contact with ignition post on back of tach. I guess my question is is a certain type of tach. needed and are my signials right, my main harness has 8 polls how does this relate to the tach.


thanks guys,
just york