How to repair a broken wire in the engine harness?

[lpvanam]

It has taken over a year of trial and error to narrow down this issue. The original symptoms were the starboard engine would die at cruising speed and then not start until the fuel relay was jostled. The relay was replaced to no avail and the pins in the relay were reset also to no avail.

i now believe that one of the wires in the harness is broken and shorted out, but the wires are tight and leave no extra to cut and repin.

This leaves multiple questions:
- Can it be repaired and if so how?
- Is it something I should take on or have a qualified mechanic do it? My impression is that I can, but need to know what parts and where to get them.

Thank you in advance for the advice.

 

[fwebster]

It sounds like you have narrowed your problems down. However, it is more likely that you have an open circuit than a shorted one. One that shorts or grounds out will usually trip a breaker or blow a fuse or fusible link. You indicate that your engine just dies but not that you have to reset breakers. I also think it unlikely that an individual wire is the cause for an open circuit, although it could be. The more likely cause is a poor connection in one of the harness connectors supplying power to the engine. We had a similar issue a week or so ago and I wrote a lengthly description it and how to attack it. I save some of the answers that take a long time to key in so here is what I posted for that member. His problem was intermittent gaues/switches, but the basic problem is the same:



"FAQ Intermittent Gauge or Dash Switches


This sounds like an open or partially open circuit between the engine and the helm station. Sea Ray makes their own wiring harnesses and you will have several harnesses used to getting power from the batteries to the helm and back to the engines. I am not sure on the 320-340DA because I haven't looked at the wiring diagram, but you probably have (1) one harness going from the switch panel on the dash to the helm station harness, then (2) one from the helm station harness to the bulkhead, then (3) one from the bulkhead to the engine. Each harness is a bundle of color-coded wires that terminates at one end with a Molex type female plug and a Molex type male plug on the other end. Here is what the plugs on the harness ends looks like.....this is representative; not exact because Molex plugs can have as few as 2 conductors and sometimes 10-12:

http://www.molexkits.com/Type/MLX/

This style of plug has removable pins that are crimped onto the end of each wire, then the pin is inserted into the nylon plug body. More than likely, one of the pins on the wire that sends power to the helm has slipped in the plug body, or a wire wasn't adequately crimped. Finding the problem is the hard part, fixing it is easy. Start by getting your wiring diagram out and locating the ignition switch and then look for the 12v source wire and note its color. Next, I would start at the helm because the chances are that the problem is on that end. Remove the switch panel and find the terminal block connecting the switches to the next harness. It will be lying behind the switch panel and the switch harness is usually pretty short so it is close. Examine the mated harness plugs and see if you notice any misalignment from the outside.......Sea Ray uses white nylon plug bodies so it is pretty easy to see thru then. Next, pull the 2 plugs apart and use a small tool to push the pins back in place if you see a misalignment, if not push then back in place to insure they are seated. While apart, check for voltage on the 12V wire. If you have full voltage, then the problem is further on down the line. Follow the wiring harnesses to the next terminal block and pull it apart and do the same thing....i.e. be sure the pins are seated and that you have voltage.


I hope this helps you narrow down the problem..........."


Hope this gives you a start and saves your trying to rip out a bunch or wiring unnecessarily.

 

[lpvanam]

Frank,

agree it is an open and not a short. Also agree that pins would be the likely cause, but I've already reset and checked them. That leaves the wires themselves. Any idea what gage of wire and size of pins are used for the relay.

 

[fwebster]

Sorry, I do not.

 

[jason78]

I would suggest you consult the Mercury Service Manual #36 ECM555 Diagnostics. This can be found rather cheap on ebay or maybe downloaded from a file sharing site (be careful). This manual should give you detailed information about the engine wiring harness and all related circuits. I have a #36 ECM555 Diagnostics Manual at home and will check tonight and see what it has. Maybe I can scan some information and send to you.

Just be careful, the last thing you want to do is blow something out on the ECM. That will cost you $$

 

[The Bill Collector]

I know this way too simple, but stranger things have happened.... I had similar issues and it turned out to be a 12volt relay switch. $6 bucks at the auto parts store and it's been smooth sailing ever since.

 

[JimG]

To the OP's title question: Its very easy to repair a broken wire... a small piece of extension wire if needed, a soldering gun, and some heat shrink tubing.

But finding that wire... that could be more difficult. The likely hood of a wire being pulled in two? Not likely, unless you use the harness as a step down into the bilge. :wow:

 

[skolbe]

My dock neighbor just went through this and he finally replaced a component (I don't know exactly which pieces) after messing with resetting the pins and having the same issue. I will ask him this weekend what he actually did. He had the exact same issue. It was not the wire.

 

[rondds]

I had a similar problem - bow thruster just stopped working. Turned out to be a wire pulled out of one of the crimped pins inside the Molex plug down at the thruster.

Can you run new wire(s) from the source to the relay, bypassing the wire that runs within the harness? If you jury-rigged something up you can get a definitive diagnosis.

 

[lpvanam]

Thanks for all the advice. I did some additional troubleshooting today. Identified the wire and pin that is having the issue. Just need to know the wire gauge, pin type/part number, and the best place to get pins for relay blocks. My other main concern is that the entire relay block may need to be replaced to make a single pin repair.

Any advice ice along those lines is very appreciated.

 

[JimG]

Pictures?

 

[lpvanam]

Not much to see... 4 wires enter a relay block with 4 pins to connect to the relay. Used a meter to find the culprit wire. It's an intermittent open and took some time to find it.


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[lpvanam]

Well, it's fixed. Went to the dealer and he hooked me up with 6" of wire and a pin. Replaced it and the open condition is gone. Now to enjoy boating... At least until the next issue occurs.


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[rondds]

NICE detective work! Electrical gremlins are a beeotch to find and correct.