Shift interrupt switch - mercruiser 140/165

[Cbastuan]

Hi everyone,
Just purchased a boat a few weeks ago, now it's pretty much the end of boating season around here so I havent taken it out on the water yet, but when I purchased it we ran it on muffs and it shifted into forward and reverse and ran nice.
I know its not the same as running it on the lake when the prop is under load, but it just wasn't possible to do a water test.
The boat originally had a mercruiser 140, and it was swapped out for the mercruiser 165 inline 6.
So, I've just been winterizing it and doing a little maintenance on it with plans to use it next year.

I noticed that the shift interrupt switch is disconnected, not hooked up to the negative side of coil or grounded. The wires are too short and won't reach the coil, but I figured the coil is further back toward the transom on the 140, so that's the reason why it isn't hooked up.

So I checked the continuity of it, with the shifter in neutral, when I hook it up to the battery and don't touch it, the light is on, when I manually push the rocker arm in, the light goes off - is this how it is supposed to function? I'm thinking it should be the other way around?

So, with the motor off, when I shift it into forward, I can hear the click of the switch, and the light stays lit on my continuity tester while in forward gear.
Shift it into reverse, you can hear the click, and the light is off on my continuity tester while in reverse gear.

Is it possible to even diagnose what's going on with it at this point? I had read the switch should not even be activated unless there is load on the prop. And taking it out on the water isnt an option at this point in time.

 

[Bt Doctur]

what year are we talking about for the 140 motor that was removed.
what type of ignition system is used.

 

[Cbastuan]

The boat is a 1975, so I would say that would be the year of the 140, the 165 in it now is a 1979-81.
Ignition system is still points, I plan on upgrading to electronic ext spring

 

[Bt Doctur]

does your shift plate use the switch with the roller or the switch with the plunger
You can use that switch with a slight change of the wiring

 

[Cbastuan]

Looks like the older style roller kind.

What kind of changes to the wiring do I have to make? Theres only 2 wires coming from the switch and they need to be hooked up to the negative side of coil, and grounded. Correct?

 

[Bt Doctur]

verify the switch again using the ohm`s scale .put the meter across the switch leads using the RX 1 setting.meter should read infinity
activate the switch, meter should read 0. Confirm this

 

[Cbastuan]

Ok, will do that later today, thanks

So am I going about checking it the wrong way then?
So when I check it with the ohm scale, I should read infinity when in neutral, forward, and reverse, correct?
Or should the switch not even be engaging without load on the prop?

 

[Bt Doctur]

being that that switch is obsolete, the new type is normally open and closes when activated. used to supply 12v to the ign system to cause a stumble/miss-fire to aid in shifting out of gear,.
used with a points system the wiring is changed to allow 12v to power the coil and create an open circuit when activated. to use the new switch you remove the wires from the + side of the coil and put them to one side of the switch, the other side of the switch goes to the + side of the coil

 

[Cbastuan]

So, if I have to replace this switch with a newer style, I would wire it into the + side of the coil.
Seeing as this is an older style, if it is working properly, should it be hooked up to the - side of coil and grounded out?
Thanks for your reply

 

[Bt Doctur]

with the meter across the contacts there should be no reading, infinity. with the switch push in, the meter should show 0 ,or a short circuit
this is called normally open. contacts close when activated
with the meter across the contacts and the meter reads 0 or a short circuit, and when pushed in the meter reads infinity this type is normally closed
will show a short circuit until push in to open the circuit.

need to know what type is there to correctly wire it

 

[Cbastuan]

Ok, thanks again, I will check the ohms tonight, and post a PIC of the switch

 

[Bt Doctur]

to use this the wire going to the ground screw must be removed and hardwired

 

[Cbastuan]

So, turns out I was looking at the trim limit switch, and not the shift interrupt switch.
That being said, I did locate the shift interupt switch and pulled it off to test it, couldn't find my multimeter so I used my continuity tester, when the switch is open, no light. When I close the switch the light comes on. I attached pics at the following URLs.
So for wiring it would make sense to wire it to the negative side of coil and ground it out, correct?
So, now that I found the correct switch, when I shift into forward or reverse, the rocker arm that engages the switch when you shift doesn't move at all, is this because there is no load on the switch?
Thanks

 

[Bt Doctur]

correct , that switch is wired to the neg side of the coil and to ground. you need a load on the prop for the switch to activate.it should never operate on land ,only in the water coming out of gear.
also know that the mounting plate for the wires contains a grounding bushing and this screw mounts it to the shift plate and also has one of the switch wires. the other screw is isolated and connects to the neg side of the coil.

 

[Cbastuan]

Perfect, thanks for your help.

 

[skippy2235]

Not to hijack this tread but, IF your engine switch activates when going into FWD while in the water, what is the fix?

 

[Bt Doctur]

adjust the cables correctly, replace the lower shift cable, remove the drive and inspect the shift mechanism, locate and repair the binding issue

 

[skippy2235]

New drive, Alpha 1 gen 2 from dealer.
New control system mercruiser.
Both new cables, shift and throttle
New shift bracket.
That leaves find binding.
I was hopping it would be a simple turn of a cable housing, just don't know which one.
So you think the shift cable from bracket to drive is binding?