shift interrupter question

jacklegmech

Cadet
Joined
May 10, 2013
Messages
25
I have a mid 90's 5.7 mercruiser engine. i had a small engine fire. I have most of the tools, a good place to work and am fairly machanically skilled. Due to the amount of work and my regular job schedule i had a marine mechanic repair and replace all problems caused by the fire. While he had it i had him repair/replace the alpha one outdrive that had quite a bit of slop (rather than go the kit repair route) and replace all cables. As he neared completion he broke his arm so i completed the work myself. That included installing the new carb, hoses etc. I was able to find the old type shift interrupter switch, tested it and it was good. I mounted it on the plate and commenced to make my adjustments and tweek the engine/ carb and get the RPMs right. I haven't had the boat in the water yet but i've run it on the water hose lots of time in the yard. I've shifted it back and forth while fine tuning the process of shifting from fwd to neutral to rev and back and forth. For about a week i didn't touch it and yesterday i ran the boat for 12 to 15 minutes. I shifted into fwd, neutral slowly and then rev and as i went back to neutral it shut off. I looked at the engine and the brown lead to the shift switch was smoking. I immediately shut the batteries off, removed the switch and tested it. It tested fine. It has no arc damage from any grounding short and I can't tell what caused the problem cause everything else on the engine looks fine. I removed the switch and it showed no signs of grounding to anything; just the damaged lead and I tested it and it functioned perfectly. It?s not sticking either. Can someone tell me what you think the problem is? The way I had it connected was to the positive side of the coil and to ground. It was working fine before this .I can?t seem to get to the water. Thank you
 

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,092
Re: shift interrupter question

need to know the engine, most are connected to the negative side of the coil and the mounting stud provides the ground.
Some electronic ignition require 12V positive to cause the engine to stumble.
But this shift interupter will only operate with a load on the propeller coming OUT OF GEAR
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: shift interrupter question

As the Doc said, we need the engine serial number, and which ignition system, Thunderbolt IV or V

Just having a stab in the dark at a drawing, the other end of the interrupt switch goes to the wht/grn wire on the side of the distributor. None of the drawings I looked at have either of the interrupt switch wires going to the coil...

(Maybe you found the source of the fire)

Chris..............
 

jacklegmech

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Joined
May 10, 2013
Messages
25
Re: shift interrupter question

I don't know if my last response went through but the engine is a 1995 5.7 Merc. I cannot be sure if it is Thunderbolt V or not but it came used with a Thunderbolt V carb cover. There isn't a engine # on it anywhere. When i had it out i looked everywhere it should have been and everywhere else. It's not there. My only mercruiser stern drive manual only covers up to 1992 and it agrees w/ Chris; the positive ties into the grn/ wht from the distributor and it is grounded to the engine grd stud, but Chris, that had nothing to do with the fire. The marine mech rewired everything and didn't install the interrupter prior to his injury. I'm about to wire it this way and monitor it closely as i test it. I'll post the results. Thanks again
 

jacklegmech

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Joined
May 10, 2013
Messages
25
Re: shift interrupter question

Hey guys, thanks for your help. I found my problem.The hot that i used to feed the swich with had a short to ground inside the harness that the marine mechanic installed for me. So as it turned out it probally would have worked the way it was 1st wired after all; But I wired the pos side of the switch to the wht/ grn from the distributor and it works great. I ran it for about 25 minutes shifting back and forth and i agree that must be the correct hook up. Once again thanks for your patience and Chris you were right, my manual is Seloc but now i have the correct manual saved on my desktop.
 

jacklegmech

Cadet
Joined
May 10, 2013
Messages
25
Re: shift interrupter question

Guys earlier i said "the carb cover read Thunderbolt V" but i meant lV. My mistake
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: shift interrupter question

.. now i have the correct manual saved on my desktop.

And a backup copy on a external HDD or stick?

Guys earlier i said "the carb cover read Thunderbolt V" but i meant lV. My mistake

As you said mid 90's I suspected it was TB-IV, but you never know, hence I asked... (My information was based on TB-IV, BTW).

Chris............
 

jacklegmech

Cadet
Joined
May 10, 2013
Messages
25
I have a 1983 Sea ray boat that is completely refurbished from the bow light to the stern light. The hull is solid. I want to keep it and the block is cracked. The engine is a 1995 merc 5.7 thunderbolt and I'm trying to replace it with a new or rebuilt and I need some good advice. I live in southeastern Virginia near Norfolk and I need a couple of options to buy from. I need to know if someone has a dealer or shop that you know that stands behind their warranty in this area (within 50 miles of Norfolk. I know a few in this area that will fight to the death to not stand behind their work. If you've had good experience please let me know. No back yard guys please because that's what I am. I need the warranty. Everyone I've called will only honor the warranty if a licensed shop installs the engine. Thank you
 
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