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1977 Mercury 850 needs wired up

T

tompands

New member
I bought this 77 Merc 850 from an 80 yr old retired outboard mechanic. This is his hobby now, he buys old merc's and goes thru them like you wouldn't believe. This thing has had EVERYTHING replaced. It purrs like a kitten. Looks and sounds brand new. I couldn't stop myself from buying it.
I bought it to put on a pontoon boat. I have a good idea how to wire it up but I'm also seeking advise. He wired a "8 wire" harness into this engine , so right now the engine has the female 8 wire plug and 2 battery wires , sitting on my engine stand.
I know the 2 cables go to the battery and I need to get an 8 wire Merc harness to run to my console. Of the 8 wires, only 4 or 5 are hooked to the engine.
I think he said the tach, trim and tilt (engine doesn't have tilt) and another accessory wasn't wired-but could easily be.
So what I'm asking is , once I get the 8 wire harness that I need and wire it into my dash, do I need to wire the dash back to the battery or does all the 12v comes thru the engine harness. All the wires were pulled out of the pontoon-That's why I'm asking question.
 
fastjeff said:
A wiring diagram would help you a lot. I suggest buying a manual or downloading one.

Jeff
Click to expand...
Yeah, except I'm wiring 2 different animals together and neither wiring diagrams (boat or motor) will answer the question I asked. I know which wire goes to what, I just need to know If the "House" gets its own 12v to the battery or it get it from the engine harness. Simple question for all you guru's.
 
The power runs through the harness to the dash/console for the tach and gauge lights.If he has used modern eight core with the colours to standard,the purple wire will carry the 12v+.Grey is the tach.Trim-tilt will be blue/white = up,green/white = down.
For everything else,bilge pump,beer cooler,electronic toys etc. needs its own fused supply and ground.I put a 20amp fuse back beside the battery and then a fused bus-bar under the dash/console.
I have a '69 Merc800 on my obsession.
 
Get a good used mercontrol and plug it in you will need the right length control cables. Keep the house wires separate and always fuse any added circuits at the battery.
 
haventaclue said:
The power runs through the harness to the dash/console for the tach and gauge lights.If he has used modern eight core with the colours to standard,the purple wire will carry the 12v+.Grey is the tach.Trim-tilt will be blue/white = up,green/white = down.
For everything else,bilge pump,beer cooler,electronic toys etc. needs its own fused supply and ground.I put a 20amp fuse back beside the battery and then a fused bus-bar under the dash/console.
I have a '69 Merc800 on my obsession.
Click to expand...

Now that's the answer I was looking for........Thank You
 
kimcrwbr1 said:
Get a good used mercontrol and plug it in you will need the right length control cables. Keep the house wires separate and always fuse any added circuits at the battery.
Click to expand...

The steering and cables are MERC, I was just missing the 8 core from engine plug up to console which I bought this week. I was just concerned about the house power which , I thought it got its own power(wasn't 100% sure) but HAVENTACLUE just confirmed for me. It wouldn't really been a question for me but someone decided to remove ALL the wiring from the console back. I'm good to go now......and thanks.
 
Does anyone have a diagram for the 8 wire merc harness to the controller ? My controller looks to be generic but it also mounts to the left unlike most. The ignition is in the dash unlike most merc's that are in the controller.
 
I wire my boats up with a custom harness, and you can do the same. All you need is a circuit to start it, work the choke, charge the battery, and get a tach output. The motor won't care how you do it!

Wiring diagrams for your motor can be found on line.

Jeff
 
As Jeff says you can use any wire as long as you remember which one you designated,which is why prefer to use the standard as the grey matter is getting a little porous.
In the old Mercontrol the wire to the neutral safety was yellow,in the newer it is yellow/red stripe.
 
fastjeff said:
I wire my boats up with a custom harness, and you can do the same. All you need is a circuit to start it, work the choke, charge the battery, and get a tach output. The motor won't care how you do it!

Wiring diagrams for your motor can be found on line.

Jeff
Click to expand...

thanks
 
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