1968 mercury 500 50hp mystery wire from control box

Hey guys, I'm trying to identity a wire comming from the control box of my mercontrol, it's a red wire and all the diagrams only show the red wire going to the starter solenoid which it is and the rectifier which they are. Can someone help me? I've got a link to the pictures I can take more if needed. Thanks! https://goo.gl/photos/xtox5SfoBHrrg3iMA

http://www.maxrules.com/oldmercs/Wiring/1966ona/25.jpg
This should be real close to yours maybe it is a aftermarket harness those wires look way too good for that old gem.

kimcrwbr1 said:

http://www.maxrules.com/oldmercs/Wiring/1966ona/25.jpg
This should be real close to yours maybe it is a aftermarket harness those wires look way too good for that old gem.

Click to expand...

Thanks for the reply, I'm thinking it's either for the choke solenoid or the "mercury switch". Is the switch basically a kill switch? My motor seems to be missing the electronic choke solenoid so I'm thinking it's probably that. Do you know what kind of signal the choke solenoid gets? I'm good with a multimeter so I could hook up my battery and test it out

So I do have an electronic choke solenoid there was a blue wire hookup up to it but no ground, I'm going to do some testing on it to make sure it actuates, I'm thinking the mystery wire was for the "mercury switch" can someone elaborate what that is?

The mercury switch is a cutout switch in case the motor kicks up it kills the ignition to prevent a runaway motor. It just shorts out the wire going to the distributor. Try to keep things color coded you never want battery posative to go to the distributor the wire coming from the distributor is the kill wire and is shorted to ground with the ignition switch turned off. Do you get power to the loose red wire with the ignition switch on and you push the choke button? The choke solenoid is grounded to the engine put 12 volts to the wire and it should engage.

Someone has done a hard wire job on her.Those look to me like domestic electrical wires,or at the very least used non standard colours to rewire.
If that wire is live,it does not go to the mercury tilt switch.There is one wire from the mercury switch to the switch box,the same terminal as the brown from the distributor to the switch box,or the blue if you have the ignition driver.
The choke wire should be grey.The body of the solenoid is the ground.When the choke button is pressed the grey wire takes 12v+ to the solenoid creating a magnetic field,actuating the plunger.
I would suggest you get a buddy and start testing each wire to see where it comes from/to.Buddy to sit,laugh and drink beer while you curse the previous owner.

Thanks for your input guys! I spent all afternoon replacing rotted out fuel lines , I checked the voltage over the choke solenoid and it has 13v going to it when I press the choke button so I'm bringing it to a shop to get them to check it out possibly find me a replacement or fix it, I'm going to test the mystery wire tomorrow and see if there's any power going through it, if it's live and I ground it to the body should it kill the motor?

Also wondering if anyone has knowledge on how the throttle should be set, I believe the last owner replaced the throttle cable and it wasn't set properly. When the warm up lever is all the way down it idles way too low and won't go into gear, I'm trying to order a tach off tinytach that would read the spark plugs to determine the rpm. I've read it should idk at about 1000 rpm but how do I set this without it?(it may take 2 months to ship) I believe I can mechanically adjust where it comes into the motor housing and I've added some pictures to the Google album https://goo.gl/photos/xtox5SfoBHrrg3iMA. The motor is firing fine and running on all 4 cyclinders. I've read up on "link and sync" but I feel like I can just adjust where the arm sits on the throttle inside the motor that runs vertically or where it initially comes in. As you can see the set idle screw is not even touching the distributor

If it is live,do not ground it.Find it's source,then figure out where it should go,if anywhere.If it was a new CDI harness,there would be a spare but with the hard wiring,I would only be guessing.
Disconnect the throttle cable,let the throttle arm against the idle stop,adjust the cable until the holding lever fits in to the barrel.A little preloading on the idle stop screw is OK,mind you too much and it will be difficult to shift from forward to neutral.
Idle should be around 850rpms.
Link and sync,isn't just to make sure that both carbs open when they should.
Here would be a good place to go http://www.marineengine.com/cart/index.php?prod_rn=253019&quantity=1