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Old 21-03-2013, 02:47   #1
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replacement wiring harness for Yamaha 9.9


I am about to reinstall a pair of 9.9 Yamaha outboards to my catamaran.

The wiring harnesses that came with the engines was a corroded mess, and is very expensive to replace. So I'm considering rolling my own. There are plenty of O-ringed plug/sockets available that look like they will do a better job than the standard setup. And making my own, I can make a long tail from the engine to the harness connection, so that I can put the plug/socket high up in the engine locker away from any chance of sea water splashing up to it.

My question is - I need some 7-core cable to do this, and what is most easily available is wire designed for wiring trailers. This has a cross section of about 1mm square, and is designed for a load of 5 amps at 12v. Would this be sufficient for making up a harness (the longest will be about 8 metres long). I think the power from the lighting circuit is run from the regulator through the fat battery connection wires. So how much power runs through the harness to the remote ignition switch?

The 7-core I've removed is thicker than 7-core trailer cable. Do I need to find this thicker cable, and if so, does anyone know where I can find some?


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Old 22-03-2013, 03:16   #2
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Re: replacement wiring harness for Yamaha 9.9

A assume you are talking of the Yamaha 9.9 4 strokes, if so I have had a few of these. I never had any problem with the multipin connectors on my catamaran but did give them a spray with contact cleaner and silicone grease from time to time. They were almost constantly wet when sailing, the connectors looked mickey mouse but worked.
You are right that the charging output goes through the starter motor cables so the loom does not need to take that current. My guess is that the biggest current draw will be to energize the starter solenoid. No idea of the current but guess in the region of 5A for a short period so the cable will not burn out. The only issue I can think of is that the volt drop across your very long loom plus the volt drop on the battery from the starting current could cause the starter solenoid to drop out giving you a succession of 'clunks' but no start. The only other significant current draw is the electric choke if you have that version, but I cannot believe that would be a problem.
Trailer multicore cable is usually plain copper multi strand and that will not last in the marine environment, it will rapidly corrode inside the insulation and prove very difficult to maintain a good connection. You need tinned copper strands and good termination.
You could always make up your own cable with cable sleeving and 7 cores of 2.5mm cable. In the UK I have sourced 2.5mm tinned copper conductor cable with a thin sheath. The other issue is the connectors. High current, marine proof multi-pin connectors that last are not cheap. It may be more worthwhile trying to source the Yamaha bits on ebay.
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Old 22-03-2013, 07:55   #3
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Re: replacement wiring harness for Yamaha 9.9

Worst-case, you can simply buy single marine wire of the proper gauge(s) - they don't all have to be heavy, do they, and bundle the7 wires in tubing, or wrap with tape or spiral wrap, etc.

Try to arrange it so that the connector gets sheltered as much as possible. Or invest in a good high-current multi-pin connector, use connector grease, and if you don't need to frequently open the connection, tape over the joined connectors.
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Old 22-03-2013, 12:55   #4
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Re: replacement wiring harness for Yamaha 9.9

I've found some 7-core wire that can carry 11 amps at 12v, and at £2 a metre, I figured I'd better give that a go. It's not tinned at that price of course, but I'll take extra care at the connections.

I might forgo the plugs and sockets altogether and just run the cable all the way to the ignition switch. If I want to remove an engine, I'd have to pull all the cable out, but I can route it to make that a fairly easy job.
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