Discolored wire

[Per Walthinsen]

When doing some reconfiguration of the wiring to the Pollak 7-pin flat spring connector on the trailer I had some difficulty getting the tail/marker lights to work, Traced it down to poor contact at the plug.

The stranded wire (14 or 16 gauge) had a black coating on each and everyone of the strands (looked sort of like it was black anodized) and I thought it might be some kind of corrosion, so I stripped it back 2-3" to get some fresh wire to the contacts. Sanded a lot of it off and got decent contact, but the discoloration continued well into the wire, potentially all along the wire for all I know. Two or three wires were like this, but the rest were nice and shiny.

I was under the impression that copper corrosion turned green, so I'm wondering whether this is in fact oxidation from being overheated instead. No other signs of overheating. Anyone have knowledge of this kind of discoloration?

[Byron Kinnaman]

When doing some reconfiguration of the wiring to the Pollak 7-pin flat spring connector on the trailer I had some difficulty getting the tail/marker lights to work, Traced it down to poor contact at the plug.

The stranded wire (14 or 16 gauge) had a black coating on each and everyone of the strands (looked sort of like it was black anodized) and I thought it might be some kind of corrosion, so I stripped it back 2-3" to get some fresh wire to the contacts. Sanded a lot of it off and got decent contact, but the discoloration continued well into the wire, potentially all along the wire for all I know. Two or three wires were like this, but the rest were nice and shiny.

I was under the impression that copper corrosion turned green, so I'm wondering whether this is in fact oxidation from being overheated instead. No other signs of overheating. Anyone have knowledge of this kind of discoloration?

You're right, they probably got a little warm.

[Per Walthinsen]

Byron,

Thanks. (Your response time seems overheated too, under 2 minutes, no less)

[Brian B-P]

I've seen lots of this sort of effect (which I assume is corrosion), including on every wire that I've encountered in my Boler's clearance lights, and in places where I have no reason to suspect any overheating.

It may be that corrosion in the presence of the insulation incorporates impurities which turn it black; also, I have noticed that many older copper-roofed buildings have a very dark "patina" (rather than the ideal green), especially in areas where they would be particularly exposed to dirt. Copper wires are not pure copper (I have no idea how much of other metals is used), so the corrosion product would not be pure copper oxides.

[jim munson]

With copper green oxide is when dry, black is when wet.

[Darwin Maring]

The copper wires do turn black under the insulation close to the connection where the elements can get to it.

Dilectric grease or liquid tape will seal out the elements. The grease is messy on the inside of a plug / jack however it is wise to put it on the actual connecters that fit together and on the bulb bases that fit in a socket.

Silley-cone will oxidize electrical connections.

[Frederick L. Simson]

With copper green oxide is when dry, [b]black is when wet.

Jim is quite right.
I see this all of the time with low voltage signal wiring in scale platform sensors that fail in wet environments. Dampness can wick for a long distance up a wire, creating a variable low resistance between the strands. In an electronic scale, the first symptom is an unstable numerical weight display (drifting values).

[Capt Ron]

The black corrosion is definitely due to moisture intrusion. I see this all the time around boats ... it's one of the reasons that marine grade wire is tinned ... it's very difficult to keep moisture out over the long haul around boats. Tinned wire at least helps slow down the corrosion ...

Liquid electrical tape helps, so does using an electrical grease on the wire before you crimp on a terminal ... a marine electrician I know says that you can't make a good crimp terminal connection without a little grease on the wire.

Marine stores sell heat shrinkable terminals with epoxy inside that also work well ... don't use silicone as a sealant or any other goop not designed for electrical service ... most contain acids that are worse than nothing at all. I recently took apart an extension cord plug (used outside but not on the boat) that I had sealed up with silicone a few years ago ... the screw terminals were crumbling wads of rust despite being totally encased in silicone.

[Pete Dumbleton]

Dielectic grease may indeed be silicone grease (not to be confused with silicone sealers and caulks) -- I just buy a little round container of plumber's silicone grease and keep it in my tool box tray.

Translucent White Dielectric Grease

Be sure that any electrical connection that you make scrapes the surface between the two metals so the grease is pushed out of the way, otherwise you might just be insulating the connection because the stuf is NOT conductive, it's intended to seal out corrosion and even to prevent conduction (as in the case of high-voltage sparkplug wires).

[Per Walthinsen]

Thanks for the input, all. I'm planning to trace the other end of the wires inside the trailer to see if there is any evidence of this black coating. That should put to rest the question of whether the problem is resistance heat or moisture corrosion. The use of dielectric grease is likely part of the solution, but I may have to cut the affected wires back and graft on new wire before I do that. I've worked out a different way of protecting the end of the cable bundle and the plug, so the exposure to moisture is likely over. If the problem had been heat from resistance I'd be looking at LED replacements for some of the bulbs in order to lower the draw. We'll see. Thanks again.

[Joe MacDonald]

Per; sounds mostly like water damage to me. The description you gave is typical of what I see on snowmobile trailers after a winter of use. If the ouside insulation was not discoloured, then you don't likely have a problem. You could also try putting in a 10 amp fuse, if it doesn't blow then there are no current draw issues.
Just make sure the fuse is after the trailer plug, so it doesn't supply the tow vehicle lighting as well, this likely would be too much.

[Darwin Maring]

A friend of mine that works on salt-water boats had a trailer that the lights would not work because of current drain (Minor Shorts) in the wiring.

He said they replaced the lights with LEDs and the current draw was so low on the LEDs that the LEDs worked perfect even though there were still current losses in the wires.

CRIMP SCHOOL: Only crimp your connection once. If you do it a second time, you tend to loosen the first crimp. Source: Phone Company and Military Electronics School.

Dielectric grease and shrink-wrap should seal a connection tight.

Hot wire: If the wire got hot, it will discolor the colored covering such as the red covering turning a dark red or burnt red. Same with the other colors.