Early '76-78 M46 overdrive switch confusion

[spock345]

I just rebuilt and installed an early '76-78 M46 today and noticed something odd when I had it all wired up just like the diagram in the '77-78 greenbook but it let me enter overdrive in all gears, including reverse (I have not reversed the car with an enabled overdrive).

What in the world is going on here?

 

[hiperfauto]

The 4th gear lockout switch isn't working properly. It should only pass current when in 4th gear.

 

[spock345]

The 4th gear lockout switch isn't working properly. It should only pass current when in 4th gear.

I tried two, one bench tested as good. That one didn't pass current at all.

 

[hiperfauto]

Either you got 2 bad switches or there's a problem with the shift mechanism. New switches are pricey.

Contact Overdrive 240

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vp-autoparts.com

 

[spock345]

I am hoping there is not an issue with the shift mechanism. I am not sure what I'd do if there is.

 

[hiperfauto]

Is the lockout switch in the top cover or the adapter housing for the overdrive?

 

[spock345]

Is the lockout switch in the top cover or the adapter housing for the overdrive?

Adapter housing for the overdrive.

 

[hiperfauto]

Then you need this switch. The original 2 prong switch was replaced with this dual function 3 prong one. You need to determine which 2 prongs make contact when in 4th gear. We have a bunch of these in storage and will give you a better price than VP if you need one.

Back-up lamp contact 3-pin

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vp-autoparts.com

 

[spock345]

Then you need this switch. The original 2 prong switch was replaced with this 3 prong one. You need to determine which 2 prongs make contact when in 4th gear. We have a bunch of these in storage and will give you a better price than VP if you need one.

Back-up lamp contact 3-pin

...

vp-autoparts.com

I'll check if I have one on one of my m40/41 top covers. If not I'll reach out.

I do want to say borrowing those tools from you made this job easy and the four speed section shifts so nicely with new synchros and bearings.

 

[hiperfauto]

Yeah, it's the same switch used on late M40/M41 top covers for reverse lights and seat belt warning light.

 

[spock345]

I've got one extra switch. I'll install that today and see how it goes.

 

[spock345]

Well, that all works with the three pole switch.

 

[hiperfauto]

Awesome, glad you got it sorted.

 

[spock345]

Awesome, glad you got it sorted.

I did notice the three pole switch and the one originally in the gearbox had a different length. I guess the one I got with the gearbox didn't have the reach to actually contact the shifter mechanism.

 

[hiperfauto]

I think the 3 pole switch has a longer travel on the plunger to accommodate both functions.