7-Pin Connector Gets Too Hot

[wlooper89]

I took the trailer out to test and set the new trailer brakes maximum voltage. Upon returning home I unplugged the 7-Pin connector and it was very hot. The rubber of the molded connector had become soft and deformed around the running light pin. I usually turn on the running lights day or night and have not noticed this before. Some time back I added a wide trailer 3-light bar but otherwise the lights are the standard Little Guy ones. All the trailer lights are incandescent and shown in the photo below.



I cannot really see a connection between the addition of trailer brakes and the overheating tail light connection. There is a wire from the brake pedal switch in the tow vehicle to the brake controller, but the brake/turn signal pins and electric brake power pin were not overheating, just the tail lights pin. The brake controller gets its power hot off the battery positive via an inline fuse. No fuse blown in the tow vehicle but obviously too much current at the 7-pin connector for the tail light pin. I normally unplug the trailer from the tow vehicle right away upon arriving home so I feel that I would have noticed if the connector was overheating before this.
Any suggestions or ideas would be most appreciated. I am clueless as to why this happened.

Bill

PS I am not sure of the best term to use for "tail" lights, but will use that since it is short and easy. In this topic I will use the term “tail lightsâ€

[mikeschn]

My first thought is you have a short...

but I'll have to defer you to the experts...

Mike...

[Ageless]

That kind of resistance should have blown a fuse. Most times heat is generated from dirty or corroded contacts.

[Larwyn]

Sounds like a loose connection. Either the wire going to the pin or the one to the socket or it could be poor contact between the pin and socket socket.

It is true that the loose contact will cause a higher resistance which generates heat, but increased resistance decreases current so no fuse should blow in that case. A visual inspection could reveal a loose wire. If not, you can read the voltage drop across the connection, depending on how much wire you include in the test you should read very close to zero volts, anything over 1.5 to 2 volts would indicate way too much resistance. I'd bet on the loose wire myself.

[zukimoo]

loose wire, wire shorting out or even possibly a bad light fixture. Take a look at the fuse for that circuit and see if someone installed a fuse that is bigger than it calls for. what you are describing should pop the fuse....if someone installed a bigger fuse then it might not pop it and it could all go up in smoke,

Years ago I was driving my 74 CB200 and we hit a bump....it wasn't a big bump but the lights and engine went out. We pulled into a parking lot and I found the main fuse busted. Being smart/stupid I grabbed a small key of my ring and stupidly installed it into the fuse holder....well it started and ran...I got about 2 miles until everything started and turned on...all the lights and the starter...went to turn the key off and burnt my fingers.

Towed the bike home and in the morning I found that every single wire on the bike was totally fried.....except for where it came out of the bike. Head light to tail light there was nothing left.

Lesson was...put the right size fuse and don't mess with electricity. If it pops the fuse there is a problem.

[wlooper89]

I'd bet on the loose wire myself.

Sounds like a good bet. The mechanic who installed my hitch and trailer battery charge wire earlier, recently added the trailer brake wire to the connector at the hitch. Something could have come loose when he did that. I'll open up the connector on the hitch and take a look.

Thanks everyone for all the ideas. I feel sure one of them will be the solution for my problem and will post the results when it is fixed.

Bill

[wlooper89]

The tail light connection looks okay in the 7-pin hitch connector, so I will try adding this relay where the tail light wiring runs through the trailer tail light compartment.

http://www.etrailer.com/p-TR38665.htm

The original tail light #14 wire will power the relay and I will add a #12 wire from the trailer 7-pin connector, 12V positive, to pass through the relay to power the tail lights. I will use some of the original #14 wiring to the lights but split them into groups so they will not all be on a single #14 wire.

According to the relay description some tow vehicles need this item to complete the tow package. My tow vehicle wiring was after market, probably with no relay and the trailer does have some extra 80" wide lighting, so hopefully this will help.
I am optomistic that this will solve the problem and will add a post with the results.

Bill

[Larwyn]

Bill, I would still check the current draw on that circuit as well as the voltage drop across the connector before considering the relay. I know that you said the connections look good but it seems unlikely that you could draw enough current to melt that connector without blowing a fuse or melting the insulation off the wire itself. There could be a high resistance connection between the pin and socket or broken wire strands inside the connection, not all bad connections actually look bad. That 14 gauge wire is good for 15 amps by my chart, which should be more than enough for the running lights. That relay could decrease the current demand on that connection but if there is a significant voltage drop across the connector it could drop the voltage across the relay coil below it's operating threshold (the sum of series voltage drops equals supply voltage). Just my thoughts on the situation, you may have already eliminated this stuff.

[wlooper89]

Bill, I would still check the current draw on that circuit as well as the voltage drop across the connector before considering the relay.

Larwyn, I will try that. Thanks! Bill

[Shadow Catcher]

A good table with a calculator at the bottom.
www.powerstream.com/Wire_Size.htm

An Ohm meter should be able to tell you where you are having a problem. Since the three light bar is new I would isolate it, take out the bulbs and check resistance and continuity.

[signs]

I think we are missing something here, you just added the wire for the brakes. Electric brakes will pull more current than the lights. Make sure the brakes are wired correctly and the short is not in that system.

[Dale M.]

My thinking, considering the sizes of these connectors and materials involved, you have a defective connector...... MY car carrier has 8 clearance lights (filaments) and 3 wide load lamps and 4 tail light filament ...That is a total of 11 small lamps and 4 medium size lamps.... Total draw should not be over something like 5-7 amps....... My 7 pin connector does not get hot even after a 6-7 hour run with full lighting on...

Dale

[Miriam C.]

When my 4-flat got hot enough to burn me I had a short to the trailer frame. Check all your wires until you find it.

[wlooper89]

A good table with a calculator at the bottom.
www.powerstream.com/Wire_Size.htm

An Ohm meter should be able to tell you where you are having a problem. Since the three light bar is new I would isolate it, take out the bulbs and check resistance and continuity.

Thanks for the chart and suggestions. The trailer brakes have separate wiring, essentially direct from the tow vehicle battery, via an inline fuse and brake controller. So I believe the 3 light bar may have been the item that made the current draw too much for a #14 wire. Perhaps there is enough cooling airflow while driving, but on this occasion I left the tail lights on while backing the trailer into the garage. In the narrow alley behind the garage it took several attempts for me to get it lined up correctly with little cooling airflow.

The relay I have ordered will send power to most if not all of the tail lights through a #12 wire that will receive power from the tow vehicle to trailer battery charge circuit. Hopefully that will correct the problem. While waiting for the relay to arrive I plan to test the amp draw of the 16 tail lights to satisfy my curiousity. All 16 lights are incandescent. If the current draw is way high that might indicate a short.
Thanks to everyone for your suggestions.

Bill

[Dale M.]

So now you have switched the problem from the tail light circuit to the battery charge circuit......... You will be just moving the "load" to a different connector on the 7 pin..... Unless you want dead battery when you arrive at camp site...... Remember as you use current/voltage from battery, vehicle charge system will try to replenish at same rate....

Think it may be simpler to actually find problem and fix it..........

IF connector is getting hot, problem is in connector its that simple..... Doubt seriously its a wire gauge issue....... We tend to rely to much on charts and calculations and not real world practicality/observation.....

My Chev pickup has aux battery feed fused at 40 amps... This tells me connector is designed to operate at a high current rate... All contacts in my 7 pin RV style connector are same style and mass so all should be good for high amp load..... IF you are having a problem with connector getting hot at somewhat less current rate, the problem is connector....

Dale