shift interrupter switch and some other wiring issues.

[84EdH]

I have a 1979 MC 1 transom plate and outdrive. I have installed a 1995 Alpha 350 engine. I have the wiring diagram for the thunderbolt 4 ignition. I see that the interrupter switch basically connects ground to the coil, when the y plate is activated. When I do a continuity test by touching one end of tester to black lead, the other to brown, I do not get continuity when the y plate is pushed........does this show my switch is bad, or am I missing something?

 

[Don S]

Re: shift interrupter switch and some other wiring issues.

To properly test for continuity, you have to disconnect all the other wires to the switch. Then test from wire to wire. No continuity when activated, then the switch is bad.

One thing to watch for, is which wire is hooked where. The black wire MUST be screwed to the terminal on the terminal block that mounts the block to the plate, other wise you will just be going to ground all the time.

 

[84EdH]

Re: shift interrupter switch and some other wiring issues.

thanks again Don. you made me think of the trim sender wires.......they are both black, I presume one goes to the wiring harness, the other to ground.. does it matter which?

 

[Don S]

Re: shift interrupter switch and some other wiring issues.

It doesn't make any difference which wire of the switch goes to which terminal of the terminal block. But the white green wire coming from the distributor can not be on the screw that attaches the terminal block to the shift plate. That would just ground out the ignition and you wouldn't have any spark at all.

 

[84EdH]

Re: shift interrupter switch and some other wiring issues.

I understand. you are a good teacher!

 

[84EdH]

Re: shift interrupter switch and some other wiring issues.

double checked my interupter switch, it is bad. cheap thing only lasted 33 years......

 

[Don S]

Re: shift interrupter switch and some other wiring issues.

They are also NLA (No Longer Available)

EDIT: Well that was easier to find than I thought.

View attachment Shift interrupt switch avail.pdf

 

[84EdH]

Re: shift interrupter switch and some other wiring issues.

luckily, I bought a 1979 century like mine for $100 for parts......included alpha drive and decent trailer. I just pulled the interupt switch from it, and it tests good on continuity.

if I had not had this, is there a substitue ?

 

[84EdH]

Re: shift interrupter switch and some other wiring issues.

well after rebuilding an engine last year only to find rotten stringers and transom and replacing everything bad on my 1979 boat due to sentimenal reasons, spending 3 days aligning the engine, re-cutting glassed in stringers and numerous other rookie do-overs.............I deserve a break!

 

[Don S]

Re: shift interrupter switch and some other wiring issues.

I edited my post with a service bulletin. Not a real replacement by any stretch. Problem is, with the new plates you don't have the reverse lockout capability. Then when in reverse the drive will come up. So then you have to replace the pump to the new style, or just hit reverse gently and for short bursts, or hold down the down button for the trim when in reverse.

 

[84EdH]

Re: shift interrupter switch and some other wiring issues.

using reverse like that would be a pain, especially when docking. hopefully my 33 yr. old replacement part will hold up......

I will tag that service bulletin to my favorites just in case.

thanks Don

 

[Dahondaboy]

Sorry to post on such an old thread but I have an 85 mercruiser 5.7 and I have went from the stock ignition to a Mallory unilite Now I realized that I really need the interrupter to function as it was a bear to get in nuetral. Can I just hook the green/white wire to the coil negative?