How do I access wires inside Mercruiser harness plug

[bbook83]

The male prong wires coming out of the plug on my 1974 140 are hooked to wires that are colored differently from those shown in the manual and those on the female side of the plug. I uncovered the wires as they come out of the male plug, but I can't tell which prong they are on. I don't see a way to split or otherwise open the plug. Can the prongs be pulled away from the plug or the plug opened somehow in order to see which wire is connected where?

 

[Alumarine]

I don't know how easy that would be but you could use a multi meter with a sharp probe to trace the wires.

 

[mjf55]

Exactly as Marc said. Multimeter and you can use a pin to insert into the wire and check from there.

 

[bbook83]

I should have thought of that. You can tell wiring isn't my strong suit.

 

[Scott Danforth]

this is the molded plug? if so, get a new harness

 

[bbook83]

It does appear to be a molded plug in that it is all one piece and has no visible means of opening. Are you suggesting a new harness because there is no way to change wires on a molded plug?

 

[Grub54891]

There is no way to change the wire colors, or pins in that plug. Shouldn't need to anyway, unless they are broken for some reason. Then you would need a new plug/harness.

 

[Silvertip]

Electdricity doesn't care what color the wire is. Wire color is used for circuit identification. Buy a small pack of straight pins in the sewing section of any department store. Use a pin to pierce the insulation and then use an ohm meter to determine which pin is what color. Or you can go to the other end of the cable and using the ohmmeter determine which pin corresponds to which color. And after you figure it out -- what difference does it make. The plug and receptacle only connect one way so the pin ID on the diagram is all you need.

 

[bbook83]

Comments by all are understood. All I am trying to do is figure out which wire attached to a male plug matches up with the wire on the corresponding female prong. Using the pins should work. Thanks to all for the help.

 

[Grub54891]

Just be sure to put a dab of liquid electrical tape on the pin holes when done. The hole may be tiny, but it will allow moisture in to the wire over time, and it will corrode. Seen it to many times, and hard to find when diagnosing electrical issues.

 

[Scott Danforth]

Plugs are keyed

 

[bbook83]

I used the straight pins as suggested by Silvertip and was able to identify which wire was on which prong, except that there is crossover continuity on two wires that are "sharing" two pins that appear to be at the root of my problems. The male prong plug was left in the boat during extended transom and engine mount repairs while the engine was out. There must be corrosion or water inside the plug, which is also 42 years old. The engine harness and female plug look good, so I would like to preserve the cannon plug setup. If I cut the male plug open, I don't think I can preserve much. I have seen some used engine to dash harnesses on eBay, but have not seen any new plug/harness availability. Any ideas?

 

[bbook83]

I managed to overcome my wiring shortcomings and realized that he hot wire from the battery side of the starter solenoid and the wire from the alternator are connected at the ammeter, so continuity is present on the prongs for each with both wires. Fortunately, I first resisted the urge to cut the plug open. The alternator wasn't charging, and I replaced it with a duplicate from NAPA, after adding the marine spark arrestor, but the new one didn't charge either. It turns out the first alternator had been converted from a 3 wire to one wire internally, but duplicating it by the exterior appearance gave me another 3 wire. Once I got the proper one wire alternator installed, all was good in the charging department.

 

[Alumarine]

Glad you got it figured out.
Just so you know some 1 wire alternators won't initially start to charge until the rpm's get up to above 1200 or so.
Once they kick in they will charge at lower rpm.

Is it an ammeter or voltmeter that you have?
If it's an ammeter they can be more trouble than they're worth with old wiring.

 

[bbook83]

Sorry I didn't see your response till now Marc. I put in all new gauges. The set I bought, and probably all new ones, included a voltmeter rather than an ammeter, so I put a hot wire to the voltmeter in the dash, but left the ammeter wired in as it was and tucked it underneath the dash. Probably old school, but I can still check it if there are problems.