Mercruiser MC-1, Alpha1 shift interupt

[holorinhal]

I have a couple questions about the shift interrupt system and shifter controls.
​I have an '81, MC-1 drive 260 Mercruiser. I am having trouble with shifting from forward and reverse, into neutral.
When shifting, the controls or cables feel like they are binding. It is very hard to go from forward to neutral and from reverse to neutral and when it does click into the neutral position, the drive stays into either gear that it is coming out of. with a little work of the control, it will eventually release into neutral. This only happens when in the water, under load. When on the trailer and on the muffs, the shifting is effortless and shifts freely.

Things that have recently been done.
I recently had to pull the drive and engine, to replace the two rear freeze plugs. SHIFTER AND SHIFTING, WORKED PERFECTLY BEFORE THAT. After the engine was reinstalled and re aligned and the drive reinstalled, I performed service adjustments, on the control cables, at the shift plate and checked for the adjustments and tolerances and every thing is within specs and adjusted properly, except the lower shift cable, adjustable stud and slot. At first I had the stud adjusted to the wrong bottom end of the slot, but have since corrected it to the bottom on the right end of the slot, toward the reverse lock out valve.

Question#1- Could the shift interrupt, not working properly, or being out of adjustment, be causing the hard shifting and binding feeling?

Second thing that had been done. I have been having trouble with my tac working intermittently. In the process of trouble shooting, I disconnected the tac signal feed in the wiring harness, from the coil and the tac. I then ran a separate jumper wire, from the coil straight to the tac, to see if there might be a short or broken wire, in the harness.

Question #2- Could, disconnecting the tac signal wire, have disabled the shift interrupt switch?

 

[achris]

Q1 yes.
Q2 only if you removed the interrupt switch wire inadvertently.

 

[Bondo]

Question#1- Could the shift interrupt, not working properly, or being out of adjustment, be causing the hard shifting and binding feeling?

Ayuh,.... With the motor idlin', push the switch on the shift plate, the motor should die,....

My guess is, ya missed those wires,....
One from the coil's (-) terminal, the other to ground,...

 

[Fishermark]

Second thing that had been done. I have been having trouble with my tac working intermittently. In the process of trouble shooting, I disconnected the tac signal feed in the wiring harness, from the coil and the tac. I then ran a separate jumper wire, from the coil straight to the tac, to see if there might be a short or broken wire, in the harness.

Question #2- Could, disconnecting the tac signal wire, have disabled the shift interrupt switch?

You should have two wires on the negative of the coil. One (probably black) goes to the distributor points. The other, (probably grey) goes to the tach. BUT - it also splits off and goes to the shift interrupt switch. So by disconnecting the tach, you also disconnected the shift interrupt switch.

 

[holorinhal]

You should have two wires on the negative of the coil. One (probably black) goes to the distributor points. The other, (probably grey) goes to the tach. BUT - it also splits off and goes to the shift interrupt switch. So by disconnecting the tach, you also disconnected the shift interrupt switch.

Winner Winner Chicken Dinner! Bingo, that was exactly it! I ran at idle, manually operated the interrupt switch and engine did not die. I disconnected jumper wire and reconnected the harness wire and interrupter switch works! Thank you very much guys, I appreciate it!
I wonder if that wire is the cause of my intermittent tac operation, somehow? I will have to get a new tac and see if it does the same or starts working.