75 Formula Shift Issue

[805HD]

If you want to see if the switch is bad, better to use an old bulb type of test light. That will allow adequate current to flow thru the switch and also eliminate the 'digital' effects from most DMM's.

I used a led pod light (all I had) wired from a 12v battery through the switch. Closing the switch kills the light, with the switch open the light comes back on.

With the switch closed (arm depressed) the light will flicker if I tap the switch.

I think I need to verify down stream electrical at this point. The switch itself is suspect to me but the electrical (ground and wire to coil negative) need to be ruled out.

If problems persist after that I can turn my attention back to shift adjustment.

 

[kghost]

Wire to Coil - is not ground.
The wire from interupter switch that goes to the coil gets shorted to ground when switch closes.

So if you suspect the wire from switch to coil all you need to do is, while running engine in water or on trailer is depress switch and if engine dies, wire would be good in my opinion.

The switch is bad in my opinion. Depressing it by hand does not represent the actual depressing by the V notch.

Now, if you bend the lever of the switch about 1/8 " from roller, so roller sits a little deeper into the V notch it may make it work better. Small bending not a lot. If it improves but not 100%, bend a little more..
There was a service bulliten way back when for what I describe.

If asjustment of the arm/lever does nit belp the bite the bullet and find a new switch.

 

[805HD]

The switch has a life span. You may be depressing it far more then the shift bracket V does.

A picture would help.

Also those switches are very hard to come by and if found sell for far more that the switch itself is worth. Its worth is only with Mercruiser shift brackets.

Part Number is, and all years that used this type of switch the part number is the same.

39670A28 - Switch Some prices are anywhere from $50 -$100+​

Most locations other than Ebay will Be NLA. In the '90's they changed the switch type/design and bracket.

So if you have a "Boat Junk Yard" anywhere near you, That would be a place to find a good used one.


View attachment 37258

Heres a before and during shift screen shot from a video I took during a forward shift. I ordered a “new switch” and am going to verify wiring as soon as the boats back at the house where I can look into it.

Again, the boat shifts fine. It’s coming out of gear that’s the problem so everything is pointing to the interrupter switch and or it’s wiring.

 

[kghost]

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