TOPIC: Mercontrol with 80's 50hp

Hi everyone. We have a mid 80's 50hp merc (8 pin round connector) that we'd like to hook up to our early 70's mercontrol box (blue/black). I could make a harness that would work, but was wondering if Mercury ever provided one off the shelf? I found an adapter harness from CDI that adapts the older motors to the newer 8pin, but not vice versa. Any help would be appreciated. Thanks!!

Try to wire it to what you want the the box...all you need are the wiring diagrams of whatever wiring harness you have and this

Thanks NJ. The diagram will certainly help if I decide to make my own harness using my existing 8pin harness and a new key switch and choke. However, I was just wondering if Mercury ever sold adapter harnesses for those with the mercontrol box that wanted to update their motor. It doesn't seem out of the question, but I haven't found any info on it.

Thanks NJ. The diagram will certainly help if I decide to make my own harness using my existing 8pin harness and a new key switch and choke. However, I was just wondering if Mercury ever sold adapter harnesses for those with the mercontrol box that wanted to update their motor. It doesn't seem out of the question, but I haven't found any info on it.

excellent diagram...

this is actually a good idea to start manufacturing, does anyone know where I can source the male/female ends of the harnesses? i just did a search and cant find anything...

It's strange. CDI actually manufactures a harness that adapts the OLD motor to your NEW controls!! (see link below)

www.magemarinestore.com/mercury-replacement-engine-adapter-harness-421-4401/

The reason I like the old controls is the warm-up lever. Call me crazy, but I can't tolerate those square push-buttons in the center on the 'newer' 80's controllers. They always seem to jam up...and I've had (3) of them!!

That diagram will not help you much if you have a 1980's Merc 500 with ADI. That diagram is for a much earlier engine with battery powered ignition, don't wire it that way or you will learn all about fire extinguishers.

Thanks for the heads up! ....although I don't plan on using that side of the diagram.

I opened up the mercontrol unit that came with the boat. Unfortunately most of the wire insulations are compromised. I guess you can't see everything when you buy a boat!! The insulation literally crumbles in my hand. Anyhow, I may end up trying to re-use the choke and ignition switch.

I won't be using the tach, so all that is involved would be the hot, ground, choke, and starter solenoid wire (that I can think of). These would be directly from my 80's round pin harness.

After I solder these, is there anything I should cover the connections with for humidity protection? Thanks.

Forgot that I had the service manual. I will use this diagram since I'm only using the new wiring at this point. Only difference will be the choke since the mercontol doesn't have the push-to-choke feature.

Chip wrote:

I won't be using the tach, so all that is involved would be the hot, ground, choke, and starter solenoid wire (that I can think of).

I would run new wires for all connections here Chip, exactly per the diagram for your motor. You may decide you want to hook up a tach later! (I can't imagine not having a tachometer, they are very valuable to prop selection, tuning, etc..)

After I solder these, is there anything I should cover the connections with for humidity protection? Thanks.

Heat shrink tubing or "liquid tape" both work pretty well.

Be sure to use marine grade wire. It's tinned to prevent corrosion, has thicker insulation, just a much better idea all the way around. We can give you some sources if you don't have a supplier close to you, here's the place I use;
www.genuinedealz.com/marine-wire

Thanks Mark. You are right. I might as well wire everything while I'm at it. I assume there is an external tachometer unit that plugs into the controller? Not sure I will be tuning or changing props, but I at least want to test the wiring. Oh, and the newer harness tach connector has one more pin (4 as opposed to 3). I will have to look into this.

This project is like peeling an onion. You know the saying...... 'Keep peeling away layers and you try not to cry'. Prior to using the keyswitch I figured I'd put the ohmmeter on it and test it. Well, in the ignition position, it works "sometimes". Man that would have caused a headache when trying to diagnose engine probs. I'm lucky I found it. Looks like a new keyswitch. Funny, I wonder if that is why the original owner said it runs 'sometimes'.

Finally finished tearing down and cleaning up the controls. The wiring was quite a chore to get all the lengths correct, but I wanted it to be robust. I will probably lightly cover the solder connections with liquid solder.

QUESTION! I noticed that the keyswitch in the 'start' position only gives contact throughout the throw, but not at the end of the throw. I thought it might be a problem with the switch, so I tested another older style switch. Same thing. The newer switches give contact all the way through the throw AND at full throw. Anyone know anything about this? Thank you!

Stopped by the marina today. I ohmed out a brand new switch (PN54211T). It was also 'momentary' in the start position. Strange.