Mercury Switch

[Skeeter54]

So I've been tinkering with my 1984 Mercury 115 hp since I still cant get it to start. I pulled off the Speed idle control like advised to do and have moved on. I was reading and some said stator some said other things but I saw something on another forum that said check the Mercury Switch. They also said disconnect the Mercury Switch and crank it. some said it would start right up , which meant there was a wiring issue with a simple fix if that worked. Can someone please help me on locating the "Mercury switch". I've searched for pictures with no luck. I got a diagram off the internet for my wiring and it sure does show a "mercury switch" come off the main wiring plug with a black and yellow wire.

 

[racerone]

What is the history on the motor.---------What does a compression test show ?-----------Is there no spark at this time.------Is there a " kill switch " on the control ?------Do you have the owners manual ?---How long have you owned it ?

 

[Texasmark]

Must be talking about the ignition kill switch that monitors engine position. Back when Merc first did the I6, there were no protective devices initially. They did a lot of testing at their test site "Lake X", Florida. They would do things line slam the engines over logs and sandbars to test their ruggedness. As a result of these tests they incorporated a couple of refinements: 1 was shock absorbers and the other was an ignition kill switch for when the engine passed a certain angle with the lower unit coming up. Reason was to slop the slamming of the engine down on the transom when the prop reentered the water which could break a transom bracket or worse knock the transom out of the boat. Chris or Steelspike know where they are but may be on the Starboard (right) clamp bracket with a tab coming off the cowling to activate it.

 

[Skeeter54]

Sorry, just got it about a month ago. This is my first boat and its a project as Im learning. First thing I did was changed out the impeller. Secondly got a new battery. Cleaned the carbs with some carb cleaner (non-rebuild just surface and internal best i could). Yanked the Speed idle control because the wiring was corroded. I have not done any spark plug tests except throwing a spark plug from a lawn mower on there to see if there was any spark which there wasnt. Downside is I dont know if it was all or just the one since I didnt check them all that day. It turns with what sounds like great compression but doesnt start. I also cleared out the tank of any old fuel mix and filled it with new fuel/oil mix. Also put on a new gas line from tank to motor with an in-line primer bulb.

 

[Skeeter54]

heres a couple of pics from the diagram. I have highlighted the "Mercury switch"

 

[Skeeter54]

No Title

 

[gm280]

First you need to determine if the engine in the normal position has that switch make ground or break ground for that circuit. In other words, in normal operating position does that switch allow current to pass to ground or not. Because if it does then you could jumper around that switch to see if the engine would crank. If it opens and keeps from shorting to ground then disconnect the wire going to the switch and see if it will crank...

 

[Skeeter54]

Gm280 the problem is I don't know where it is. I've looked around everywhere but can't seem to locate it. Sorry but all new to this so I appreciate the help

 

[gm280]

SKeeter54, do you know how to use a DVM or multi-meter? If so and you have one, take one probe and attach to the place where the schematic shows a connection to the mercury switch at any of the places that wire goes and the other probe to the engine casing (bare metal not painted surface) and see what it reads (on the resistance scale OHMS). If it doesn't read anything or actually reads shorted, leave those probes in place and tilt the engine. If that reading doesn't change, you don't have any switch installed... If it does change when tilted up, trace the wire down until you locate where it attaches to the mercury or tilt switch... Other then that, I can't offer anything else without being there... :noidea:

 

[Skeeter54]

Okay I will try. I may take pics of the engine and post them to show you what I'm working with. Maybe you can point it out exactly

 

[Skeeter54]

Found the switch finally. I'll try that tomorrow. I heard if I disconnect it it should fire up. If this does happen then the connection backwards is messed up. Sound right?

 

[Dukedog]

Found the switch finally. I'll try that tomorrow. I heard if I disconnect it it should fire up. If this does happen then the connection backwards is messed up. Sound right?

as long as tha "short", solid black (bottom end or lowest side) is made ta ground and tha black/yellow (top end or highest side) goes back to tha harness it should be fine unless tha switch itself is bad...

that switch should only make contact and kill (all black/yellow wires are kill circuit) tha ignition when tha motor is tilted up way high.... disconnectin' it only removes it from tha "kill circuit" enabling tha motor ta start/run in any position...angle can usually be adjusted to allow it to start and run at angle of choice... its strictly a "safety switch".. if its bad (still hooked up) it will either let it start/run in any position and/or keep it from starting/runnin' in any position....... very rare ta be a problem part...

 

[Texasmark]

Apoplogize for my location remarks. Now it seems that this top has come up before and I learned of a mercury switch. Brings back that memory. Makes sense, get it properly adjusted, vacuum sealed will last a lifetime, follows movement of the glass bulb, perfect solution for the problem. But question comes to mind about the mercury sloshing around in rough water at high trim positions. Could make for some intermittent operation. Course they solved that problem with power trim.

 

[Dukedog]

. But question comes to mind about the mercury sloshing around in rough water at high trim positions. Could make for some intermittent operation. .

don't recall ever hearin' of any problems like that... merc did away with 'em completely in '92 on tha V6's though.. don't know 'bout tha "little motors.....

 

[Texasmark]

don't recall ever hearin' of any problems like that... merc did away with 'em completely in '92 on tha V6's though.. don't know 'bout tha "little motors.....

I know mercury is heavy and all and with very low surface tension it tends to stay in a single ball and not break up but just curious thinking about the designer that chose that mechanism to solve the kick up/slam down at WOT problem.

 

[Skeeter54]

Sorry guys but still a little blurry on this. As it sits it is black (ground) facing down and the other side dos go up. I understand the concept of it but if it's bad like you said it could cause it not to start as well correct? How do I know it's bad. Would a simple disconnect solve this to see if it starts?

 

[Skeeter54]

No Title

This thread was from another forum. Might try this and see what happens... Thoughts?

 

[Dukedog]

Sorry, just got it about a month ago. This is my first boat and its a project as Im learning. First thing I did was changed out the impeller. Secondly got a new battery. Cleaned the carbs with some carb cleaner (non-rebuild just surface and internal best i could). Yanked the Speed idle control because the wiring was corroded. I have not done any spark plug tests except throwing a spark plug from a lawn mower on there to see if there was any spark which there wasnt. Downside is I dont know if it was all or just the one since I didnt check them all that day. It turns with what sounds like great compression but doesnt start. I also cleared out the tank of any old fuel mix and filled it with new fuel/oil mix. Also put on a new gas line from tank to motor with an in-line primer bulb.

this tells me we went to tha mercury switch way ahead of time... ya need ta get tha right plugs in it and test for fire at any of 'em ta start with........stickin' one 'ole plug of some kind in it ain't gonna cut it.....
also if ya gonnabe a diy'er ya need ta track down a good OEM manual for it or ya gonna always be behind.....jmo

 

[Skeeter54]

Roger that. Thanks dukedog. Just learning as I go

 

[Dukedog]

I understand whatcha goin' thru but havin' a manual will make it soooooo much easier all tha way around... '74 1500 right? I may have a pdf for it.. if not I'll see what I can find. ya don't happen ta have a serial number do ya?