Harness issues

[Boyle1986]

Hey,
I’m having issues with finding a harness for a gen one mercury 850 harness but I can’t find any controls that will work with that harness. So my question is can I hard wire a new control or can I get an 8 pin harness and rewire it?
Thanks

 

[Chris1956]

What exactly is the issue? Newer controls will work the shift and throttle properly. Your wiring can be adapted to the new wiring. You would need an interconnection diagram. Not too difficult

 

[Boyle1986]

Just trying to find a harness that can be used with new controls

 

[Dukedog]

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[Dukedog]

get control and 8 pin harness.. hard wire at motor end or use (hard wire) 8 pin MOTOR harness ta jus plug in ta boat side 8 pin..... will need ta pay close attention ta wire colors as some may/may not (depends on year of motor) be a little different... jus take ya time and you can figure it out....................

 

[Chris1956]

Is your motor ADI ignition with 4 coils? If so, you should be able to get an ADI ignition motor harness with the round skinny plug, for a more modern 4 cylinder ADI motor, say a '90s 115HP.

This engine harness plug will match the newer controls wiring harness. You would need to route the boat harness into the motor cowling. You would also need to get a pair of battery cables and route those to the block ground and starter solenoid. and seal the entrance.

 

[Boyle1986]

A seperate set of battery wires? does the power normally go thru the harness? And then split inside the cowel?

 

[w2much]

My two cents to explain. The harness controls the power provided by the battery cables as well as the features of the motor( choke , tilt, start, stop..., ). The battery cables are not considered part of the harness. Chris is just saying you need to correctly wire both battery and harness wires.

 

[Boyle1986]

I guess my confusion is in the diagram that’s showing a power line going thru the harness. I think I’m miss understanding where the battery cables go in the cowel becuase the only opening I have I believe is thru the harness plug

 

[Chris1956]

Your old 850 boat harness includes the battery cables. A newer harness will not. Hence you will need separate battery cables, plus the new harness.

Of course you could buy new controls and harness and cut off the skinny plug and graft the old quick connect to the new wires. Usually, those old quick connects go bad, though.

 

[Boyle1986]

So I bought a new control that is an 8 plug pin that supposedly is the replacement for this model to just plug and plug if I’m understanding correctly. Here is the link to the control I bought https://www.amazon.com/Amarine-made...trols+mercury+52771a2conpatavle,aps,84&sr=8-9

 

[Boyle1986]

My understanding was that it was a plug and play kind of thing

 

[Chris1956]

If your 850 has the quick disconnect plug on the starboard side of the cowl base, it is not plug and play. Mechanically it will work fine. The separate brown wire is overheat, which you likely do not have.

If you have a 1976 or newer Merc 850, you will need to replace the engine harness with a 90's version with a matching plug, add separate battery cables and seal the remainder of the hole in the cowl base. You may be able to use any ADI engine harness, versus a specific 4 cylinder one. Not sure about that.

If you have battery power distributor ignition(pre 1976 Merc 850), it may (may) be tricky to get the right engine wiring harness. You would likely need to use an ADI ignition harness and find a way to jumper the purple ign wire to the white terminal on the switchbox, and likely need to jumper from the starter solenoid battery side, to the red terminal on your switchbox. Probably both could be done w/o issue.

Of course, if you can find the female version of the plug, you could graft your existing engine harness, to it w/o much difficulty, provided the existing harness is in good shape. Most are shot by this time. Look for insulation falling off the wires.

 

[Scott Danforth]

or you guys can simply swap the connector to a military style deutsch or amphenol

 

[Boyle1986]

Yea harness is shot. That’s why the question of just hard wireing it in and it doesn’t have a switch box I think it’s just two bus bar style connections on the starboard side next to where the harness comes in like maybe 7 wires

 

[Chris1956]

I do not have any experience with pre-switchbox (point/coil) ignitions. That would make your motor pre 1970s, I would think.

Scott is correct. A water resistant plug with the correct number of wires, might be the easiest. Hopefully you have a wiring diagram. The maxrules web site has Merc wiring diagrams, that may go back that far. Try and match your motor up.

Seven small spools of different color wires plus some crimp and solder on ring terminals, plus some good old electrical tape will make the new harness look and work well. I recommend soldering all connections.

 

[Boyle1986]

The max rules was were I was getting most of my info as to splicing an extra power line into existing harness is there a draw back to just hard wireing new controls and running battery cables thru that whole where the plug would have Ben and putting a water proof stopper plug in there?

 

[Chris1956]

The factory harness provides sufficient power to gauges. Anything else should be directly connected to the battery and run to a fuse block. An inline fuse at the battery is a good idea as well. A master shut off switch is also a good idea.

Keep in mind that those old Mercs only charged at most 9Amps, at high throttle. They were intended to keep the starting battery charged to start the motor. If you use any more power, the battery will simply run down.

 

[Boyle1986]

So what I’m understanding is the power line in the new pigtaile is enough to run gauges but I will need a seperate line to the battery for motor starting? I plan on running trolling motor and other things off a seperate deep cell battery. The current gauges are running of a direct connection to the battery becuase the whole system was gutted out of the boat and someone ran a simple system for gauges . So I will have to splice them onto the new control also for older gauges?

 

[Chris1956]

As I said in post #10, the new harness does not have integrated battery cables, like your original did. Of course, I have no idea what you have now, after your last post stated that the original system was gutted.

If you somehow use the new boat wiring harness, it will power your gauges and starter solenoid and choke, but nothing else. You will need battery cables from the starting battery to the motor ground and starter solenoid. Power to the new boat harness will come from a connection between the new boat harness and there battery cable at the starter solenoid.

Power for the trolling motor should be hard wired to the deep cycle battery with the appropriate fuses.

If you took an original wiring diagram from your motor, plus a wiring diagram that matches your new boat wiring harness, you could make an interconnection diagram. I predict that most of the wires will match up.

Your new boat harness has power (red), ground (black), choke(Yellow/black), starter solenoid(yellow/red), Tach signal(grey), ign power(purple), ignition killer wire(black/yellow) and an overheat buzzer(tan/blue). The external brown wire is for temp gauge.