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Neutral safety switch replacement- 1990 - 4.3 mercruiser

K

kirkll

Regular Contributor
I had my neutral safety switch break on me, and found out they discontinued the switch and had to buy a whole new shift control bracket that includes the new design switch…. Of course now I gotta go though the whole shift cable adjustment song and dance again. I thought I might get lucky and just leave the cables alone and have it work…. But Nooooooo….

Anyhow… I’ll get that sorted out with some fine tuning on the water.

My big question is how these switches work? I’ve got two wires coming out of the switch. One goes to the negative side of the starter solenoid and I’m unsure where the other wire goes. It’s a yellow wire with a green strip going into the wiring harness. I’m also unsure if there is a positive and negative side to the switch? Being a switch… I wouldn’t think it would matter which wire went where. But…. I don’t want to hook this up wrong and cause problems..

Any help would be appreciated. Thanks, Kirk
 
If the switch you are speaking of is on the shift bracket mounted on the exhaust elbow, That is NOT a nuetral safety switch. It is a shift interupter switch.

When activated it will kill the ignition system.

It works when trying to go from gear (Fwd or Rev) back to neutral. The gears dont want to separate and this causes resisitance on the short shift cable causing the V notch part of the shift bracket to move, activating the switch.

This all happens very quickly and when the switch activates, kills ign for a split second, the gears seperate and you get to nuetral.

So is this ths switch you are referring to?

Is one wire is white with Green stripe and one wire is black?
 
My bad… it is the shift interrupter switch. Yes… one wire I can see goes to the ground post on the starter solenoid. I tested that post to verify it was a ground post. The other could be white with a green stripe, but it looks yellow to me. I assume it goes to the distributor or ignition system somewhere. Just don’t know where…

I understand the basic function of the switch. when the switch stays open everything runs correctly. And it’s only activated during shifting. But…it will not shift correctly without it.

My old one I had a roller on the end of a short piece of spring steel and had no adjustment to center it up on that V shaped bracket. The only way to adjust it was bending the little metal arm slightly. It was tricky to get it centered up and have it engage the switch button correctly. I messed with this a couple years ago and got it working again. But it’s never really shifted smoothly in and out of gear since then…. But it worked…. The little roller finally came loose and needed replacement. That’s why I replaced it with the new shift plate assembly.

The actual installation of the new throttle / shift bracket wasn’t difficult, and went pretty smoothly. But….. and there is always a big butt messing with shift cables. The instruction’s say “ do not adjust the cables “ …. But when I got everything together it wouldn’t shift correctly. So I started from scratch and went back to basics…. I tested the lash distance in the lower shift cable and was in the 1/2” to 9/16” tolerance level and shifting in and out of forward the cable was functioning well. After determining it as in forward gear I used a bungee cord to hold back pressure on the prop while I got the cable adjusted. I set the center of barrel to center of cable mount to 6”. It was set almost 6.5” before . Then I checked the throw on the reverse cable and it was 2 7/8” . Recommended tolerance is 2 7/8- 3 1/8” . Then I adjusted the reverse cable plastic barrel to fit perfectly, then backed it out 4 turns per the specs.

Bottom line is that it wouldn’t shift into forward gear at all with the manuals pre set cable recommendations at 6”. But…. I didn’t have the thing in the water, and the interrupter switch wasn’t hooked up either…. Last time I messed with these cables I just put it in the water and adjusted it back and forth until it worked smoothly. Or should I say somewhat smoothly. I was dealing with a funky interrupter switch at the same time….

So I’m thinking I’ll just get the switch hooked up correctly and go launch the boat early this am when it’s not crowded. Then just go trial and error adjustments until it’s right…. Any further instructions ? or something I’m missing here? I’d appreciate any help I can get…. Kirk
 
Well I pulled my hair out trying to get this thing shifting right this morning. I went to a local river, put it in the water, and just tied it up good at the end of a dock out of the way. I watched a couple more you tube videos to double check my shift cable adjustment procedures, and couldn’t get it shifting right. Here is best video I found, and it’s pretty straight forward.


There are way too many you tube producers that haven’t a clue what they are doing. But I did glean a few items regarding the shift interrupt adjustment. The new shift plate does have a very slight adjustment adjustment capability on the interrupter switch. But I could not get the combination right going….. then the spring bracket, or V arm that momentarily hits the interrupter button was sticking in the full wot position. Going into the revers position, reverse it wouldn’t go into gear until I moved the throttle forward more, and the spring arm was sticking and shutting the motor down…. Seriously frustrating….

Finally the boat ramp just got too busy and I just couldn’t take up the dock space any longer. I’ll go back down there at 5 -6 am tomorrow. I’m going to head back out to my boat barn and go through the whole thing again in the cool of the evening and run it on muffs. I refuse to let this kick my arse…..

Any helpful ideas or suggestions are very welcome at this point. Thanks, Kirk
 
IF the arm that moves the switch is hanging up you need the lower shift cable replaced. It should never move on land going into or out of gear
 
I appreciate your help with this… You saved me hauling this down to the water pre maturely this morning . Much easier working in my boat barn in the shade. let ya know how it comes out. Kirk
 
Well….i found the problem. Getting some help spinning the prop why I shifted, I could not get it into reverse at all this morning. With our without the shift linkage. No amount of adjustment is going to fix that issue.

So it’s gotta be the lower shift cable , or something in the lower unit. I called my local shop that does my outdrive work, and got an appointment for Friday the 17th. He said it could be the clutch dogs, or something else besides the cable too. I’m just not set up to pull an outdrive, and have no idea how to check the lower unit out anyway if it’s not the cable itself…. I gave it my best shot.

The sad part is… That the whole reason I started messing with my shift interrupt switch in the first place was most likely too much resistance going into reverse and triggering the interupt switch. I tried using it with the switch disconnected and it was like shifting a manual transmission without a clutch. That wasn’t happening…then I broke the old switch trying to adjust it… now I can’t get it into reverse at all.

I did manage to get it shifting into forward and back to neutral smoothly with the new shift plate . That will have to work for now. I’ll use my kicker motor for docking and trailering next week. Do you see any problem running this thing just using the forward gear as long as it’s shifting smoothly in and out of gear? I don’t want to screw up the gears in the lower unit causing further damage. But I have a family camping trip this next week.

Kirk
 
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