Today's 7 blade RV trailer connector mystery

[noteven]

Brought to you by me, noteven, a self appointed electrical dummy... 

The issue:  RH turn signal / brake light no work on enclosed trailer.  

Diagnosis:

1. output from blade on truck connection - check - light blinking and beeper beeping in circuit tester. Good.

2. remove sealed beam lamp from trailer - check - connections clean and greased. Good.

3. check for signal at lamp connection, brown wire. - nope. No signal. 

4. open junction box of sealed Bargman cord from truck to trailer wires. Clean and dry. Check for signal at turn/brake wire (brown) while connected- nope. Wiggle junction box wires. Nope. 

5. disconnect cord and trailer turn brake wires at connection in junction box.  Connect jumper wire from truck blade to trailer wire. Light operates correctly. Reason that trailer wiring from junction box to rear lamp is ok. 

6. check right turn/brake wire with circuit tester for signal at junction box end of the wire. Nope. 

7. Decide broken circuit must be in Bargman cord. How? I dunno... it looks strong and sealed and undamaged... 

8. Clean the contacts on the truck and cord one more time in faint hope. Test circuit again. Nope. 

9. Connect jumper to truck and trailer wire one more time in junction box. Lamp flashes normally. Works as it should. 

10. Say phukit and go for 5 hour motorcycle ride. 

11. Return to issue this morning. Must be the cord... don't see how... hmmmm....

12. Do I want to do a whole new cord? Or put one of those junky repair ends on the existing cord? idea! (imagine Wile E. Coyote "getting an idea" image)... cut plug off, test the cord, test the plug. Could be repaired with new plug if not the cord. They don't call me a Sooper Genius for nuthin...

13. Cut the plug off neatly and carefully.  Strip and bare the end of the offending circuit on the trailer cord. Connect jumper to truck blade. yaay! lamp works as it should. 

14. Test the cut off plug circuits for continuity with test meter. Test apparatus on the known good circuits. Good, good, good, etc. - and now for the grand finale - the "bad" circuit...

and... good! Whaat?!? No!! did I cut off a good end for nuthin!? Waaaaaa!  

Now for the mystery part: 

How can the plug and it's cord both test good for continuity but not have a good signal to the trailer wire? 

15. Plug the cut off end into the truck. Remember, all circuits have continuity when tested from the blade end to the cut off wire end.  Light up tail lights, turn on signals - good, good, good and 

You guessed it - no good through the right hand turn/brake circuit when plugged into truck. All circuits good continuity through the plug when unplugged...

Near as I can figger, when the plug is installed into the truck, there must be a break in the plug blade wire connection inside the molded plug or sumpin that causes an open when it is plugged in, but closes and has continuity when the plug is removed from the truck....  

Just so you don't think this is stupid electrical problem number 1 ever I have had... ask wrknrvr Vern about using his fancy wire tracing equipment on my trailer one time... 

Anyways - I'm going to wire a replacement end on the cord... 

I will report back. 

What do you vehicle electrical diagnosis experts think? 

 

 

[Kirk W]

It is quite possible to have a bad connection between a plug and a socket and either of them could be the cause. In my own experience, I have seen more failures on the socket side, probably from moisture & dirt getting into them.

[noteven]

4 minutes ago, Kirk W said:

It is quite possible to have a bad connection between a plug and a socket and either of them could be the cause. In my own experience, I have seen more failures on the socket side, probably from moisture & dirt getting into them.

Yes and good idea to check it  Kirk - 

in 1. of my post I had signal beeping on and off from the truck socket blade. 

but is it solid?

I just connected the circuit tester to that blade and set it to beeping. I carefully wiggled that blade this way and that - signal kept coming through loud and clear - indicating nothing is loose or broken in the socket side. 

Thanks

[Kirk W]

The blade would not need to be broken to be bad. If the fit loosely or are corroded enough to introduce significant resistance they still might not work. Over time and use the connection can become loose and corroded to a point that your sharp probe will make enough contact to make the light flash, but the plug doesn't make good contact. 

[Wrknrvr]

Clean both the female and male brass surfaces as best you can with fine sand paper. Then with a pair of needle nose pliers, twist the male end just a tad. Plug it in for a test,

 

Hopefully this will make it work properly.

 

  Vern

[Darryl&Rita]

1 hour ago, noteven said:

10. Say phukit and go for 5 hour motorcycle ride. 

Start here, instead of finishing. My old trailer plug tester used a headlamp for the load, instead of LED or beeper. Make that circuit work, instead of loafing along.

[oldjohnt]

One thing to consider is a weak/resistive connection can still yield the correct voltage on a tester or volt meter HOWEVER if you place a load on it only then is there a V = I x R Voltage Drop which can make the load inoperative because you drop the voltage across the bad connection versus the load itself. I couldn't count all the bad/resistive  connections or corroded or loose fitting pins/contacts Ive encountered in 50 years of RVing grrrrrrrrrrrrrr. Bright clean shiny contacts on both the male and female portions is a must............

 John T

[Ray,IN]

I have seen trailer plugs where the contacts have lost their ability to hold tension on the prong of the other end. That requires replacement.

[sundancer268]

Every trailer I have wired, the brown wire was the running lights.  Looking at the WEB site for eTrailer, I see there are two standards.  Being as you are connecting to an enclosed trailer and not an "RV" I would bet you are wired per the "SAE" standard.

https://www.etrailer.com/faq-wiring-7-way.aspx

[noteven]

8 hours ago, Ray,IN said:

I have seen trailer plugs where the contacts have lost their ability to hold tension on the prong of the other end. That requires replacement.

This ^ is the problem. Bent prongs - all lights work - wiggle plug - running lights quit. Bend prongs -all lights work. Wiggle plug a bit right turn/brake goes out again.  No longer reliable. 

I picked up a new plug. 

 

Thanks for the replies. Hope this thread might be of help to others. 

[noteven]

1 hour ago, sundancer268 said:

Every trailer I have wired, the brown wire was the running lights.  Looking at the WEB site for eTrailer, I see there are two standards.  Being as you are connecting to an enclosed trailer and not an "RV" I would bet you are wired per the "SAE" standard.

https://www.etrailer.com/faq-wiring-7-way.aspx

Of course! Why wouldn't there be two wiring standards? 

Hydraulic fitting people also design wires?

 

[Chalkie]

9 hours ago, sundancer268 said:

Every trailer I have wired, the brown wire was the running lights.  Looking at the WEB site for eTrailer, I see there are two standards.  Being as you are connecting to an enclosed trailer and not an "RV" I would bet you are wired per the "SAE" standard.

https://www.etrailer.com/faq-wiring-7-way.aspx

etrailer usually has some good info but this confused the heck out of me. So how is my F-350 supposed to know if I have a trailer or an RV connected. It does tell me when there is something (it just says trailer) connected. And I have pulled enclosed trailers like CargoPro and large flatbed trailers like Big Tex and never had a problem. I think this may something rather arcane and etrailer went overboard on their research.

[Ray,IN]

13 hours ago, sundancer268 said:

Every trailer I have wired, the brown wire was the running lights.  Looking at the WEB site for eTrailer, I see there are two standards.  Being as you are connecting to an enclosed trailer and not an "RV" I would bet you are wired per the "SAE" standard.

https://www.etrailer.com/faq-wiring-7-way.aspx

That's crap. The 7-way standard wiring color-code chart doesn't even show a left turn signal wire. Someone was smoking something when they made that chart.

[noteven]

Update - I bought a replacement plug. It happens to be the one sided style but that was what they had. No way for it's contacts to move away from the truck socket contacts. 

I opened it up and "yaaay!" The wire colors were marked beside the connections and were correct compared to oem plug. This replacement plug was made in Taiwan and of nice quality. So they aren't all junk. Now all connections to tow vehicle are working I will open it up and apply the dialectric greases. 

Now to repair 3 clearance lights...the rest are working.

I open the first one's lens. It's up high on the rear of the body. Must be the bulb. Bulb tests good continuity. Power is present in the socket..... bent the little wire contacts out a bit, plug in bulb, nuthin.... lens'sz are old and brittle and gravel tattered - don't want to open up another to borrow a bulb - USA made trailer, lens and lights are unknown to our local suppliers. 

No replacements bulbs in stock. 

30 miles to town tomorrow... 

Mebbe it's time for that "LED conversion" ... 

Edited August 11, 2021 by noteven

[sundancer268]

I converted my Motor Home, Travel Trailer and Utility Trailer to LEDs and I am quite happy with the results.  The Tail/Brake light housings on the Utility Trailer were not available in LED so I just replaced them with new Incandescent and added some new LED Tail/Brake lights in a new place.  I also could not find LEDs for the front clearance lights on the Motor Home so the replacements were Incandescent also.  I am still looking but they still are not available so far.

[Kirk W]

1 hour ago, noteven said:

Now all connections to tow vehicle are working I will open it up and apply the dialectric greases.

Dielectric grease, or tune-up grease, is a silicone-based grease that repels moisture and protects electrical connections against corrosion. ... The grease does not conduct electricity, so it shouldn't be applied directly to the mating surfaces (pins and sockets) of an electrical connection.

1 hour ago, noteven said:

Mebbe it's time for that "LED conversion" ... 

The old style lights were prone to several problems internally that can be difficult to detect. Most use a spring that gets weak over time, sometimes the buttons of the socked become misshapen or corroded, and several other problems. If the socket is bad you may get it to work but it will probably not last. 

[oldjohnt]

I also converted BOTH my home and RV to LED lights. They draw far less current, more lumens of light per watt, produce far less heat, and for the most part (sure there are always exceptions) last much longer.

 I'm a believer (50 years of RV's and trailers etc) in after a thorough cleaning using dielectric grease to prevent corrosion, works great...  

John T  Live in the RV at the Lagrange Tractor Show