b93 Mercury Sport Jet 90 kill circuit

"G'day!
I have a '93

"G'day!
I have a '93 Mercury Sport Jet 90 in a Bayliner Jazz. This is essentially a Merc outboard mounted to the chassis and with a direct drive impeller system.
The trouble is that the ignition kill circuit is faulty. To start the engine, I can pull apart the black/yellow wire near the ignition control module on the engine; the engine won't turn off, even with the key switched off and removed, till I reconnect that kill circuit.
The kill circuit is engaged all the time. I have determined, to the best of my ability, that the kill circuit runs from the keyed ignition switch, to a deadman switch (with a lanyard to attach to the driver in case the driver is tossed overboard), to a rev limiter, and then to the ignition control module on the engine.
I started at the deadman switch, and it ohms-tests as open with the lanyard attached, and as shorted with the lanyard yanked -- this is with the two wires UNattached to the switch. With the two wires attached, there is a short (ground) read across the leads no matter which position the deadman switch is in.
This means that there is a faulty short in the circuit somewhere else. I therefore replaced the ignition switch, but that didn't fix the problem.
The entire wiring harness is in great shape, and the wiring harness bundle that has a multiple-wire connection at the engine is clean and corrosion-free and still has waterproof grease in it.
This leaves me with a fault in either the rev limiter or the ignition control module, as I see it.
Does anybody have any experience they can share with me here before I start buying even more parts?

Thanks!
--Jim"

"How long have you had this bo

"How long have you had this boat? Can you bypass the safety switch? If it starts with the switch bypassed, it may have been replaced with the wrong kind (normally closed instead of normally open). If the problem just started, get a manual- I don't remember exactly how the kill circuit is wired but it may be a switchbox issue."

"Hey, Jim. Here are my respons

"Hey, Jim. Here are my responses in the order you posed the questions:
Bought the boat this spring. The boat was running fine and one day, it just cut out while we were using it. Had to have it towed back to the launch, etc....
I can bypass the safety switch, and the boat will NOT start either with the wires hanging free, nor with the wires connected to each other.
The problem just started. I have a Clymer's manual for that drivetrain series (Mercury 90 and 120 Sport Jets), but it does not address this particular issue; there is troubleshooting included for engine problems specific to that drivetrain, not for any particular boat's wiring harness.
That's what I'm thinking: that it's a rev limiter or switchbox issue.

Question: is the "switchbox" the same as I was calling the "ignition control module," which is the black box on the side of the engine itself? I have the newer-style bullet connectors on all my electronics, and all the electronics are sealed up with molded plastic. I have literally checked every connector, but haven't gone so far as to ohm out every wire. As indicated earlier, this boat is in great physical condition, and I don't suspect a broken or corroded wire or connection.

--Jim

Bayliner Jazz

"If the Clymer manual shows th

"If the Clymer manual shows the schematic for the electrical, see if you can bypass the rev limiter or disconnect the overheat sensor (which activates the rev limiting feature). The overheat sensor is on the head, near the top and has a tan/black wire attached to it. Unplug this and see if anything changes.

Switchbox, IC module, basically the same thing.

Look for fusible links, too. They're on the motor. ALso, make sure the main harness is plugged in completely."

"Jim N.,

Okay, I traced th

"Jim N.,

Okay, I traced the Black/Yellow wire around the engine and found that the rev limiter is isolated at the end of the circuit. I pulled the connection to it, leaving the rest of the kill circuit intact, and YES! -- the engine starts and stops by using the key. I can also start the engine and yank the deadman switch, and the engine cuts off.
I am very happy about this. I am now wondering if the rev limiter is neccessary, or VERY neccessary. If I leave it disconnected till I get a replacement, can I use the boat cautiously? Does the rev limiter work constantly to maintain a preset high-end RPM limit, or does it work more like a momentary switch, killing the engine till it is restarted?

Thanks for your time!
--Jim"

"You want to keep a rev limite

"You want to keep a rev limiter on the motor. If something allows the RPM to go too high, it gets ugly. I had to replace two SportJet power heads due to A) resting on a sand bar with the motor running and it overheated, welding a piston to the head and B) the owner got annoyed by the low oil warning buzzer so he disconnected it and the motor scattered completely."