Merc 120 SportJet Fried Brand New Rev Limiter Box

[96SportJet]

Finally after the long process of troubleshooting this ignition system It ended up being the rev limiter that was bad not allowing the boat to run. So I bought a new one yesterday and put it on. I took the boat out today and it ran amazing. But then somehow the rpm limiter box got shorted out or something because now it's doing the same thing. What would cause this to happen. I can't keep buying these $50 boxes and keep troubleshooting. Can anyone help me out.

This is a 96 Merc 120xr SportJet in a Sea Rayder F16

Thanks
-Dennis

 

[96SportJet]

Re: Merc 120 SportJet Fried Brand New Rev Limiter Box

Forgot to add, My rpm gauge doesn't work right either. It will kinda jump around unless the engine is under heavy load.
And if I pull the saftey kill switch and I put the starter switch in the kill position it will pop the engine fuse.
Also i think when I had the ignition kill switch in te kill position I thought I smelled electrical burning. Then it wouldn't start again.
Maybe this will be something obvious to someone but I am lost.

 

[96SportJet]

Re: Merc 120 SportJet Fried Brand New Rev Limiter Box

I took the rev limiter box apart today and it burned up a resistor.
Why is it when I use the kill switch to turn off the motor it shorts something out? I can't find any frayed wires or anything.

 

[CharlieB]

Re: Merc 120 SportJet Fried Brand New Rev Limiter Box

You have a poor ground between the ignition switch and the motor.

When either switch is used to kill the motor by grounding the ignition module it overloads the poor ground, feedback into the rev limiter smokes the resister.

Clean and tighten all grounds on the motor, then clean and tighten the male pins in the cannon plug by slightly opening the slot on one side of each pin with an exacto knife, careful, it can make you bleed.

Double check wire connections at the motor, specifically color coding to ensure no cross-plugged colors.

Remove the fuse and substitute a test light, pull the saftey kill switch and I put the starter switch in the kill position, the light should be OFF unless something is shorted. Unplug components one at a time until the light goes out. Once you identify the area of the problem repost with your findings.

 

[96SportJet]

Re: Merc 120 SportJet Fried Brand New Rev Limiter Box

I removed the fuse and put in a test light and it would light up dim and then go out. So I traced that down to be the Tach. I don't know if it is supposed to do that or not but the tach is causing that.

Now if I pull the safety lanyard and hit the kill switch the test light will light up really bright. I can't find anything that is grounding out. But you can def feel the fuse wires getting hot and then it will pop the fuse after about 6-8sec. Is that just a safety feature or is something wrong.

 

[CharlieB]

Re: Merc 120 SportJet Fried Brand New Rev Limiter Box

Something is WRONG.

Key OFF lanyard pulled or not, the test light should remain OFF. Nothing should be ON unless the radio is wired straight into the + side of the ignition switch, pull the radio fuse, both if it has a constant hot to preserve preset channels. Does the test light go out now?

Unplug the grey tach lead on the rectifier, if that makes the test light go out then the rectifier is bad, shorting through the tach.

It bothers me that pulling the lanyard blows the fuse, could one of the lanyard switch wires be incorrectly plugged into a + such that instead of grounding the ignition kill to ground it shorts + to ground?

Clarification, no, not + to ground, it is plugged in and when the lanyard is pulled it is connecting + to engine KILL, shorting and blowing the fuse AND killing the rev limiter, you are lucky that it hasn't taken out the ignition module.

Key OFF, lanyard plugged in, test both wires to the lanyard switch, if one reads + then trace it back to find where it is plugged into power instead of to a ground.

 

[96SportJet]

Re: Merc 120 SportJet Fried Brand New Rev Limiter Box

N/A

 

[96SportJet]

Re: Merc 120 SportJet Fried Brand New Rev Limiter Box

I did all that with no joy.
Here is a little run down:
1. Key On, Lanyard Pulled, Starter Switch in Kill Position = Test Light On
2. Key On, Lanyard Hooked, Starter Switch in On Position = Test Light Off
3. Key On, Lanyard Hooked, Starter Switch In Start Position = Test Light On

No matter what I unhook, as long as it is in configuration #1 above the light will stay on. I am thinking that is going to happen no matter what, right?

What I can't figure out is why my box burned up. The lanyard was hooked up the whole time when it burned up. I had the start/run/kill switch in the kill postion with the key on. Was it chance or do you think there is still something wrong. I wish this was a I/O with a chevy, at least then i'd know my way around.