1978 Mercury 700 wiring issues

[1971 Lund sport 17]

Hello new to the forum. Need some help. I just bought a 78 merc 70hp. The wiring is messed up and I don't know what everything is. It came with no battery cables and I have no idea how to put them in and tie them to the key. Also I have a 4 pin harnesscoming out of control box.which I don't have the other half. Any help would be greatly appreciated.

 

[1971 Lund sport 17]

Update: found a wiring diagram looks like a run a power to the top of the starting selanoid and ground some where?. Do you I ground it from the battery to boat or do I ground battery to the motor somewhere ?

Thanks

 

[Chris1956]

A 1978 Merc should have a quick disconnect plug on the starboard side of the motor. The two battery cables should emerge from the "boat side" of the wiring harness, and be routed and connected to the battery.

On the engine side of the wiring harness the battery cables should emerge from the moulded quick disconnect plug. The positive battery cable goes to the large post on the starter solenoid. The negative side is grounded to the lower cowling, just behind where the fuel line is connected.

Does that help?

 

[1971 Lund sport 17]

Yes it helps. The wiring diagram I found showed power from battery to selanoid and then grounding to engine which I did. I can turn it over and electric choke works as it should so I think im good to go. I have a weird 4 pin connector coming out back of the hand controls and no idea what it's for.

I also have another question. I have a 71 Johnson 60 on the boat now and I'm swapping with the merc will the bolt pattern be the same. The merc also has tilt and trim.
Thanks

 

[Chris1956]

The bolt pattern on the Merc is very likely different from the Johnson, especially since you need 4 bolts just for the PTT cylinders..

Are you sure the connector on the control is not 3 pins? A 3 pin connector would be power, ground and tach signal. Not sure what the fourth pin would be.

 

[1971 Lund sport 17]

My fault turns out it's 3 pin. But I am able to turn motor over the way I have it hooked up. Does that mean I won't be able to shut it off ?

 

[Chris1956]

Your motor should have an ADI ignition system, with 1 coil per cylinder. The orange wire should be grounded by the ign switch to stop the motor.

 

[1971 Lund sport 17]

Okay thanks for the help got it on the boat and have been out fishing 4 times now. All is well. I'm getting mixed opinions on the year of my motor the serial number is 4830841 would like to get a water pump kit for it and just wanna know if you can tell the year

 

[Chris1956]

The maxrules web site has a Mercury serial number to year table. It should give the definative answer.