1978 Mercury 700 Control Box

[starman779]

I just purchased a 1978 Mercury 700 70 hp Outboard S/N 4982717. This motor has less than 200 hours on it and has been stored since 1981. The problem is that the remote control box was left in the boat which was sold years a go. I have searched the internet and called Mercury to try and get a number for the box especially the cable which is a 6 pin connection. No trim and tilt. I came close a couple of times but the pin configuration did not match the motor.

 

[Chris1956]

That motor likely has the old external quick disconnect on the starboard side of the motor. There are likely lots of them around used. Search flea bay under MerControl.

What wire colors do you have? I would expect that motor, if 1978, to have an ADI ignition and multiple coils. I thought it would have 7 wires in the harness, with one unused in the engine harness. The extra wire allowed you to swap motors to a battery powered CDI ignition motor, like the 1150 of that year.

Alternatively, you could convert it to an 8 pin harness. You should be able to find an engine harness with an 8 pin round male connection that would adapt to your motor. The mechanical of the controls for that harness will work with your motor as well.

 

[starman779]

I have attached a photo of the connection on the motor and the coils. I have not tried to take the wire harness off the motor or apart yet so I can't tell what colors I have coming from it. This will have to be done sooner or later because the insulation is flaking off. I expect most of the wires will have to be done. I do have a wiring diagram which shows the colors coming from the connector. I would like to get a complete control box or I will have to rig up a temporary ignition switch to see how the motor runs.
Thank you for the fast reply.

 

[Chris1956]

I have not seen a wiring harness like that before. It is different than my '77 and my '73 Mercs had. You do have ADI ignition which helps narrow it down.

I would see what Crowleymarine website recommends. Look up your serial number on the maxrules site and see what year it thinks you have.

If you can get a wiring harness number from Crowley, the web probably has a replacement.

Alternatively, an 8 pin ADI wiring harness, and an 8 pin control should work.

 

[starman779]

This is a 1978 US motor. I know this motor has been a bear to get info on, which I don't understand why this particular one. I have come close with a #D04C15376 Control. Seller says Mercury and the connector is very close but the pin configuration is one pin off but it appears to have the right connector. From what I can find the harness on the motor is a 84-73204 (73204). the mating connector I can't find a number.

 

[Chris1956]

Info on controllers has always been hard to get, for some reason. The good news is that the function of the wiring is the same as most motors.

The only differences are the electrical plugs. Since you need an engine wiring harness anyway, maybe source an available (Sierra) ADI harness and compatible boat harness wiring. That wiring should be able to be soldered to the existing control.

 

[The Force power]

I have to rig up a temporary ignition switch to see how the motor runs.

You can put a jumper wire in the left row's bottom to the one above to complete the ignition-circuit - to kill remove jumper
These harnesses were used on 65hp / 3 cyl. also

 

[starman779]

I noticed that the same connector was used but just a different configuration on the 65hp.
What you are suggesting is to get the harness and change the connector to a more common. This could be done by splicing say a 8 pin round connector to the harness. Considering I don't have a control box yet I could probably use one from a bigger motor say a 85 or 90 hp with the trim and tilt wires from the control box being ignored.
I didn't quite understand this jumper connection. Can you give me the colors of the wires to jump?
I want to thank you for your help.
George

 

[The Force power]

I noticed that the same connector was used but just a different configuration on the 65hp.
What you are suggesting is to get the harness and change the connector to a more common. This could be done by splicing say a 8 pin round connector to the harness. Considering I don't have a control box yet I could probably use one from a bigger motor say a 85 or 90 hp with the trim and tilt wires from the control box being ignored.
I didn't quite understand this jumper connection. Can you give me the colors of the wires to jump?
I want to thank you for your help.
George

The larger motors will not have the same plug but yes, everything is possible to hook-up the wires direct.
Jump wire into these terminals will fire the engine & to kill the engine pull the jumper-wire.
Hook up some battery cables booster cables to the starter to crank the engine and take a compression reading off all cylinders BEFORE you buy any harness / spend money on this thing
(there's usually a reason why it has been parked since 1981)

 

[The Force power]

What is the serial#

 

[starman779]

What is the serial

What is the serial#

#4982717

 

[starman779]

The larger motors will not have the same plug but yes, everything is possible to hook-up the wires direct.
Jump wire into these terminals will fire the engine & to kill the engine pull the jumper-wire.
Hook up some battery cables booster cables to the starter to crank the engine and take a compression reading off all cylinders BEFORE you buy any harness / spend money on this thing
(there's usually a reason why it has been parked since 1981)

I know the prior owner quite well. There was nothing wrong when put in storage. This is a barn find. The mistake he did was to get rid of the boat with the control still inside. I will run a compression check on it now that I know how to jump start it. Thanks for the tip about spending the money on parts. That has definitely been a consideration when I started this project.

 

[The Force power]

#4982717

This still shows with the distributor but I believe the Harness / wiring set-up for the most part are the same

 

[Chris1956]

ADI motors are wired quite differently than the distributor ignition illustrated. Go on the maxrules web site and find the correct wiring diagram for your motor, by year, if you can. If not, a 1977/78 Merc 850 will be pretty close. It has 4 cylinders and therefore 4 coils, but the stator wiring and engine wiring harness are pretty close.

The killer wire on your motor is likely orange or salmon in color. It would be grounded to kill the ignition. With the boat harness unplugged, the ignition will be on.

To crank your motor, add jumper cables from the battery to the engine, Battery negative to a good part of the block, and battery positive to the starter solenoid large cable that runs to the harness connection. Now jumper the yellow wire on the solenoid to the battery positive jumper and she should crank, and start. Choke to kill. There should be a manual choke knob with a wire on it.

 

[The Force power]

ADI motors are wired quite differently than the distributor ignition illustrated. Go on the maxrules web site and find the correct wiring diagram for your motor, by year, if you can. If not, a 1977/78 Merc 850 will be pretty close. It has 4 cylinders and therefore 4 coils, but the stator wiring and engine wiring harness are pretty close.

The killer wire on your motor is likely orange or salmon in color. It would be grounded to kill the ignition. With the boat harness unplugged, the ignition will be on.

To crank your motor, add jumper cables from the battery to the engine, Battery negative to a good part of the block, and battery positive to the starter solenoid large cable that runs to the harness connection. Now jumper the yellow wire on the solenoid to the battery positive jumper and she should crank, and start. Choke to kill. There should be a manual choke knob with a wire on it.

YES, I stand corrected!
My apologies I was too focused on the shape of the plug & I did not see a wiring diagram for a 3 Cyl. 70 hp with that shape plug to post.

 

[The Force power]

This would be it, so NO JUMPER REQUIRED

 

[starman779]

Gentlemen, thank you your assistance. It is deeply appreciated. I will give it a try to crank and get the compression test. Then test the wiring before I even try to start it up. I am sure some fuel lines will have to be replaced after this length of time. That diagram of the control will certainly help. I wish they had a number for that remote so possibly I could find one and save myself having to change the connector on the motor.

 

[The Force power]

Gentlemen, thank you your assistance. It is deeply appreciated. I will give it a try to crank and get the compression test. Then test the wiring before I even try to start it up. I am sure some fuel lines will have to be replaced after this length of time. That diagram of the control will certainly help. I wish they had a number for that remote so possibly I could find one and save myself having to change the connector on the motor.

IF....you're planning on making a permanent hook up, you could make a hard wire set up?

 

[starman779]

I will probably do that. A lot easier than trying to figure in another box unless I get a match.
Thanks again for everything.