Shift Interrupt Differences

[BeeEl]

Okay so I got new lower unit installed and took boat out. It goes into gear fine but is a real bear to get out of gear. I had a buddy manually actuate the interrupt switch and it acted fine. I am going to go ahead and adjust the shift cable per the video. What I am trying to find out is what is the difference between the 2 different interrupt switches on the points style ignition system versus the EST? Mine apparently used to have the EST but someone went back with a points system. I intend to change back to EST over the winter. But for now, I noticed in the book there are 2 different part numbers for the switches and one has a "terminal block". Apparently mine still has the switch from the EST. I really don't know what to do. Can someone please help? My kids are gonna kill me if I don't get this thing going soon.......
Here is my current setup

 

[frank246]

Re: Shift Interrupt Differences

Your current set up is point style.
The difference in the switches is no and nc.
For your set up you need the no switch that shortcuts the coil neg. to mass when the switch operates.
Eyeball the switch function when a buddy shift out of gear, the switch must activate at about 1/8" of movement.

 

[alldodge]

Re: Shift Interrupt Differences

Okay so I got new lower unit installed and took boat out. It goes into gear fine but is a real bear to get out of gear. I had a buddy manually actuate the interrupt switch and it acted fine. I am going to go ahead and adjust the shift cable per the video. What I am trying to find out is what is the difference between the 2 different interrupt switches on the points style ignition system versus the EST? Mine apparently used to have the EST but someone went back with a points system. I intend to change back to EST over the winter. But for now, I noticed in the book there are 2 different part numbers for the switches and one has a "terminal block". Apparently mine still has the switch from the EST. I really don't know what to do. Can someone please help? My kids are gonna kill me if I don't get this thing going soon.......
Here is my current setup
View attachment 206078

Noticed your switch seems a bit bent up like someone tried to adjust it by bending it. It probably just needs to be bent back where it should be and adjusted correctly or needs a new switch because it isn't closing internal contacts correctly.

 

[Bt Doctur]

Re: Shift Interrupt Differences

http://www.boatfix.com/merc/Techbk/94/94hsa2.pdf

 

[achris]

Re: Shift Interrupt Differences

http://www.boatfix.com/merc/Techbk/94/94hsa2.pdf

You need to be looking on page 12 of the above PDF...

 

[BeeEl]

Re: Shift Interrupt Differences

Wow, awesome document. Thank you so much. I've got it now where it shifts in and out nicely. Seems to be working correctly. I would like to go ahead and get a new switch since mine is so heavily "modified". I'm having trouble finding just the switch, but I'll get there. However, I did notice in my book that the points style switch grounds the ignition when closed (which is why you need a no switch). The EST version interrupts the 12v supply going to ignition (which is why you need a nc switch). Am I reading that correctly? I didn't notice that until it was mentioned about the nc vs. no switch. Thanks again!

 

[achris]

Re: Shift Interrupt Differences

Yes you are reading it correctly. From previous posts it looks like you have EST ignition system.

Unfortunately most of the older interrupt switch are no longer available. In order to maintain the existing engines Merc has released shift plate kits to modify older engine to take the new switches. That comes at a price... Over $100 for the kits. The original number for your switch was 87-19752A3

The service bulletin regarding the kit is -> http://www.mercruiserparts.com/bulletins/001/04//2002/EN_01.PDF

Chris.......

 

[BeeEl]

Re: Shift Interrupt Differences

Ok, now you lost me. I really think I have a new style plate. It just appears to me that someone could have simply replaced the nc switch from the est with a no switch from a donor unit? Why can I not just put the nc switch back on it when I go back to EST? Obviously I would have to change the ground back to keyed 12v also. . . .

 

[achris]

Re: Shift Interrupt Differences

The switch in the photo in your opening post is the OLD style switch. I have no idea if that's an NO or NC switch. You'll need to measure it to find out. All the new style switches are plunger type, not roller.

Chris.......

 

[BeeEl]

Re: Shift Interrupt Differences

Oh, ok. I wasn't aware they were different style switches. What about my switch plate? Does it look like the new or old? Better yet, is there a pic of the est setup so I don't continue to ask crazy questions?

 

[fishrdan]

Re: Shift Interrupt Differences

Points and EST use the same type of shift interrupt switch, NO. The difference comes in how it's wired, points have the switch going to ground, EST has the switch going to +12V.

When timing the EST ignition, you have to connect and disconnect the shift interrupt switch wires along with jumpering 2 white wires, while the engine is running, to put the ignition into base timing mode. (The 12V applied by the shift interrupt switch is just a signal voltage.) The shift interrupt switch does not run (power) the EST ignition, the shift interrupt switch just turns off the spark when 12V is applied. This happens very quickly when shifting out of gear, so the engine stumbles instead of completely turning off.


If that switch is working properly, making and breaking contact, I'd use it. The arm being bent is not out of the ordinary as that's how the switch is adjusted, bend the arm for proper clearance, proper operation.

For the original problem, it sounds like the shift interrupt switch is out of adjustment since your buddy stumbled the engine by pressing the switch.

 

[BeeEl]

Re: Shift Interrupt Differences

Just to recap (in case anyone else uses this thread for their own troubleshooting):
Both EST and points system could technically use the exact same switch. In a points system, the switch "sends" a ground to the ignition to temporarily kill it. In the EST system, it "sends" a 12v signal to the distributor (module within) to tell it to temporarily suspend ignition? All of this happens very quickly, almost without knowing except for the fact you can actually change gears when it's working! This switch has been discontinued and been replaced by a different style switch which necessitated the change to the shift plate as well. Hence the expensive kit. Yes, my switch still actuates cleanly. I will keep using it and dig through some electronic books I have access to in an effort to locate this original style switch. Forcing us to buy the expensive plate is just crazy.
Thank you all again so much for your help.

 

[fishrdan]

Re: Shift Interrupt Differences

Check out this thread, I adapted an off the shelf switch to replace my NLA shift interrupt switch. Took some cobbling/tweaking, but it works.