Need wiring harness help

[Mercruiser 120]

i bought a 1981 boat that was purchased new in 1981. The deal was so good, something had to be wrong. It was. The engine had water in it and block is cracked. I bought a running 1970 Mercruiser 120 and dropped it in. Everything was great. Everything bolted up and I was almost in the water. Went to plug in my big wiring plug to the new female end and they don’t match up. On the male end of my 81 plug it has three bigger posts in the plug but the 1970 engine now in my boat only has room for 2 big posts and seven smaller ones.
I don’t know what to do the wiring is so complicated.

 

[Bt Doctur]

so just swap over the engine harness

 

[Bondo]

Ayuh,..... Welcome Aboard,.... BD's got yer answer,.....

 

[Mercruiser 120]

The wires on the ‘81 female harness are different colours that’s all? Do I just match big to big and positive to positive?

 

[achris]

Do you have a wiring diagram for each engine? If you do, just move the corresponding wires across. For example, on the '70, the water temp sender has a green wire, on the '81 it's tan... You are going to have to do it that way for all of them. You're also (probably) changing from a voltmeter circuit to an ammeter circuit, so be careful there.

I think if I was doing it, I would just remove the harness off the 70, put it aside. Remove the harness off the 81 and place it on the 70, and just follow the '81 wiring diagram to connect it up... That would probably be the easiest...

Chris.........

 

[Mercruiser 120]

[No message]

 

[Mercruiser 120]

Chris can you read my post when you open up my picture please

 

[Mercruiser 120]

Should I buy a ‘70 wiring plug like in my picture and rewire my dash or just take the female receptacle off of my ‘81 and match different colour to different colour?

 

[Bondo]

Should I buy a ‘70 wiring plug like in my picture and rewire my dash or just take the female receptacle off of my ‘81 and match different colour to different colour?

No,.... Just put the original wirin' harness on the older motor,..... The WHOLE harness,....

 

[Bt Doctur]

your trying to reivent the wheel, stop and read the posts. Use the harness from the old motor
the plug in the picture is from what, Your boat or the donor boat?

 

[Mercruiser 120]

Can someone tell me what colours the wires are on a 1970 Mercruiser 120 for: 1) black to engine ground and ground on solenoid 2) grey to ignition coil 3) tan to water temperature sensor 4) orange to alternator 5) purple to alternator 6) red-purple to circuit breaker and starter slave solenoid 7) yellow-red to starter slave solenoid 8) light blue to oil pressure sender 9) brown-white to terminal block trim sender.
My ‘81 engine had a 50 amp Circuit breaker my 1970 engine doesn’t

 

[alldodge]

Here is the 120 and 140



And current

 

[Mercruiser 120]

The male end is from my current boat, original equipment but it fits the engine that I took out.

 

[alldodge]

Understand, but you should have the info for the new an old. The old is in the wiring diagram, the new is in the color code.

One issue is the Orange,
the old goes to oil pressure sender on the motor and to the gauge
the new does not go thru the plug but goes from the alternator to the starter post

AS BT mentioned, if you used the harness off the 81 motor and put it on the older motor this will work, just note where the wires go on the motor

 

[achris]

In short. Strip the old (1970) engine back to a long motor, drop it in the boat, and build it up from the parts of the cracked 1981 engine, which includes the harness.