Oh those $#@$@%() Wires !!!

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February 3, 2008

Howdy !

We all have our “Pet Peeves” and one of mine is bad wiring practices. One of my biggest “Peeves” is reserved for those ever be darned 3-M wire splicers. Now the idea is good. A simple one-wire-in and two-wires-out splicer that you just lay the wires into and crimp it into place. No stripping the insulation off of the wires, no tape to hold it together and quick.

However, folks just seem to go crazy with the dang things. Last week a buddy of mine brought his 5th wheel trailer over because the tail lights “just stopped working” and could I fix it if he brought the adult beverages. Well, I hooked up my trusty light and brake controller test machine to the trailer and the lights worked just fine. Hummmmn

Hooking my tester to the trailer electrical connector on the pickup we tried the brakes, tail lights and turn signals and nothing worked. Now as you might already know, I’m in my more “advanced” years and crawling on the ground is something not on my current list of hobbies – but – he is a friend so under the truck I went.

This is what we found:

Bad Wiring 3-M splicers

Those first quick clips were put on by the RV dealer when he took the truck in to have the hitch and brake controller installed. The second were done during one of his travels at a shop that “fixed” his intermittent tail light failure.

We tend to forget that inside these quick-clips are little dinguses that look kinda like a itty-bitty tuning fork that is pressed over the wire when the clip is crimped into place. The wire gets nicked and over time and vibration the nick can turn into a cut wire. Water and dirt can also get into these things causing corrosion and make the splice fail.

Cequent, Bargeman and other wire and brake controller companies make adapters that you just plug into the tow vehicle’s wiring harness for the brake controller and the trailer’s light/brake plug. No cutting, splicing or mess.

For motorhomes that tail light plug for the TOAD on the back of the rig and the splices into the TOAD’s light circuts may be done with these critters so it might be a good idea to take a look at the connections and see what you have. I’ve seen some pretty high dollar coaches with these things on them so don’t assume that everything is custom wired ! In fact, it your rig is used you might want to check it completly to make sure that some previous owner didn’t use these things.

If you MUST use one of the 3-M type connectors just make sure that the quick-clip is taped to prevent crud from getting into it and the wire is mounted to prevent strain and vibration from cutting the wire.

Well, that’s my peeve for the day –


The Old Ranger

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  1. Fred Cory

    Many years of electrical wiring has taught me that: (1) the strongest and best looking connection is a properly soldered joint covered by shrink tubing. The diameter of the joint should not exceed the diameter of either wire. (2) if a plastic 3M type connector is used, always overwrap it with electrical tape to keep it closed and eliminate vibration. (3) butt connectors are good if not exposed to moisture. Again, overwrap with electrical tape. Liquid tape is OK and preferred in marine applications. A disadvantage is that it cannot be removed like standard tape can. (3) wire nuts? Hate ’em. They too need to be overwrapped in ALL applications. They are the most likely to come unscrewed due to movement and vibration.

    Any and all wiring that will be forever concealed needs special attention. Do it once, secure it to the extent of overkill, and rest assured that it will not develop a ‘hidden’ problem.

  2. Ellen McClintick

    Ken Priest has my vote. I used to installed A/C units, alarms and radios systems in gray market imports. I started out using butt connector and such, but after I gained more experience, I used solder and heat shrink tubing. Not only was I 100% sure of the connection, but it looked neat, clean and professional.

  3. Jack Murphy

    Being an aircraft electrican for 23 years, a licensed electrical contractor for 12 years and a Neuclear Weapons Mechanic for 12 years in the USAF. I state. Treat all RV wiring as if you were working on aircraft. tag all connections with same color wire use nothing but stranded wire never smaller than 14 gauge AWG. On all splices use the Barrel Type of splice. Single wire to single wire. If you have 1 wire in too 2 or more out glue in a Terminal strip. With1/4-20 Lock nuts. Glue it to the chassis with Construction adhesive. Tie with linen string all harnesses every 6 inchs bolt them down. Remember wires only break at connection points. The NEC ( National electric code ) states wiring must be held firmly in place within 12 inchs of connection points. FAA Manual states 6 inches.
    Your RV is mobile and it flexes all the time and stuff flies up under your unit.



  4. Don Brod

    Well i know there is some real good info here, I also hate those wire splices. But i must
    comment on Dave Dommels responce Wire nuts are are not to be used on stranded wire they were designed for use on solid copper house type wiring. they also have moisture and corrosion problems. if using on stranded it would be best to tin the wire ends. Probally not a big deal for the speakers. When I attended RV tech school we were told no screw on wire connectors were to be used on RV’S.

  5. Dave Dommel

    After reading all the comments about 3m connecters, or scotch blocks. Being a new to the trade as a Tech. The one thing that was impressed on us students at school was to never use them anywhere, inside or out the rig. A good example was the other day I was PDIng a trailer fresh from the factory and they started using them for the speaker connections from the radio harness to the wires run for the speakers and the rig had 9 speakers and 5 of them did not work. Guess what? I cut them out and used wire nuts instead
    and all 5 speakers worked. So my line of thinking is take the extra time to do it right, using wire nuts, butt connectors or solder for it will save you in the long run.

  6. Mike Steffen

    Howdy !

    Good comments !!

    First Doc. The liquid tape is good stuff. I’ve used the 3-M version for years and it does work well on permenent connections, heck, I even pour in into butt connectors when I want a real sealed connection !

    Kirk, you are correct that one of the big problems is the person putting the things on and the cheap junk out on the market – but – the fast fix is not the best way to do things on wires. I’ve also gotta agree with Ken and you both in that if you use the red ones for 20 to 18 guage wire, the blue for 16 to 14 gauge wire or the yellow ones for 12 through 10 guage wire the odds of wire cuts from cheap connectors or different metals oxidation and crud are real.

    I also agree with Kin that using one of these connectors is a problem waiting to happen! reguardless of brand or where they were made.

    Reckon that it just irks that heck outta me when I see these things used because someone was too lazy to do a good solid job in the first place, esp when we have to pay for it !! Or when I’ve gotta fix the thing. Had another guy a few years ago who came into the shop with brake problems on his travel trailer. Turned out that when the dealer installed the brake controller they use a 3-M quick connedt and placed it almost onto the switch. It had cut the wire clean through so no signal to the brake unit and no brake lights ! I had to replace the switch because there was not enough wire left on it to get a good connecton.

    Like I said, it’s a peeve of mine – – Thanks for the comments !!


  7. Ken Priest

    Continued: Further, the actual area of the point of contact between the metal blades in the connector and the wire is very small. Odds are, the metal in the blades and the metal in the wire are different. Different metals often react to each other over time. A twisted and soldered connection or even a crimp connection offer a much larger area of contact. To me, to install a 3m connector now is to ask for problems later.

  8. Ken Priest

    I totally agree. I personally prefer to solder and heat shrink when I can. I don’t care what the directions say. 3M connectors are for people who are in a hurry, are not technically minded or don’t care what will occur down the road!

  9. The problem isn’t with the 3M connectors, but with the way that people use them and in the fact that so many knock-off products are around. Issue #1 is that if you take the time to read the directions, they state quite clearly that the type you describe are not for use where exposed to weather or to moisture!

    The second problem is that so may get whatever is cheapest and think that they have the ones made by 3M. The fact is all you need to do is “read” one more time and you will find that you have some China import that is made for cheap metal what does not hold up.

    These things are just like most good products. They are only good when properly used as the instructions state!

  10. DocHoliday

    Excellent advice. On the note of corrosion. There is a neat new entity called liquid electrical tape.
    Once you have your wire harness, or your end-to-end butts, or other electrical connections together, try this tip.
    Seal the end of the connections with liquid electrical tape. Don’t goop it up. A small dab on the area where the connector and wire meet will self float around the connection and seal the area to water/dirt/ dust.
    Safe Travels