Trailer lighting Issues

[Bartman]

First time poster,,
I have a 2000 Coleman Tacoma. Bought it used in 2006 and it has been a great trailer.

On our last trip the trailer lights stopped working on the way home.  I'm pretty sure I checked them before we left but I cannot swear to that.

I have tested the tow vehicle and it is fine to the 7 pin plug.

I checked the plug one the Tacoma and it is giving me a continuity reading on all pins. I'm using the audible ohm setting on my meter. I disconnected all of the wiring and checked the plug by itself but of course it is fine. I then ohmed across the wires and all of them showed continuity to each other and the frame. Every single one of them!

I connected a battery to each wire and grounded it to the trailer and each one worked as it should have.

I?m thinking that I have a short, or multiple shorts in the trailer. I am in the process of searching the forum but haven?t found anything specifically helpful yet.

I'm at a loss. I'm not the best at electrical stuff on automobiles to begin with.
Any guidance would be greatly appreciated.

[GlennS]

Hi,

(If you don't like wordy answers, you best go on to the next post!)

First a note about meters. When you use the continuity test function on a digital meter, it does NOT need 0 ohms (which would be a short circuit) to sound off. It varies among meters, but its not uncommon for them to beep with 10-100 ohms between the leads. When the filaments of a bulb are cold, their resistance in ohms is much lower than their operating resistance, which they reach in less than 1/2 second once the power is applied.

The typical 1157-type bulb like you probably have on your Tacoma, when cold, will ohm out at less than 1 ohm for the brake light and around 2 ohms for the taillight! Guaranteeing that meter will beep for all the lights using continuity tests. This is why all the lamp pins beep to ground/frame when you check them.

(If you care, when the bulbs are hot in operation, the resistances would be around 6 ohms for the brake lights and 24 ohms for the taillights.)

Since you checked the bulbs individually, it's not likely that you have a short or you would have burned something up with the battery test! Remember that shorts cause high currents to flow, usually resulting in one or more blown fuses, or burned out wires.

The next thing to check for would be a missing/bad ground connection. On my Coleman Taos, the ground wire to the frame is just a rivet, and if it works loose you could have a sometimes-ground/sometimes-no-ground situation.

Use the ohms function (not continuity) to check the ground pin on the trailer connector to the frame:
-first short the leads together and see what that reads. Should be between 1.5 and 0.2 ohms depending on the meter and leads. Make note of that.
- now check the resistance between the ground pin and the frame. Will be higher than the leads-shorted reading.
- subtract the two readings, which gives you the actual resistance between the ground pin and the frame. This should be less than 1 ohms, since the resistance of 40 feet of stranded number 16 copper wire would be about 0.2 ohms. The wiring on your Tacoma should be at least as large as #16, and there shouldn't be more than a 40 foot round-trip between the ground pin and a forward point on the frame.

See what you find with that test and it may give you some clues.

Let me know if you have more info and I'll try to help.

Glenn

[Bartman]

GlennS,

Thanx for the great information. However, I failed to include some more information.

In between ohming the trailer connection and testing the truck connection I took apart the trailer plug and made sure all the connections were good.  The plug just pulled off so I don?t think the connections were good and tight.
I put it all back together and plugged it into the truck.  When I turned on the running lights everything seemed fine.  When I turned on the left blinker all the lights on the trailer blinked, even the running lights. The same thing happened when I tested the right blinker.
This made me nervous so I disconnected it and began the ohming of the trailer.

Is there any reason you can think of for something like that to happen?

It is dark now so it will have to wait until tomorrow.

[wavery]

You either put it back together wrong or some of the little wire strands are wandering off like a 2-year-old and touching places that they shouldn't. :p

Check here for your color code. My bet is, you have 2 (or more) wires in the wrong spots.
http://images.google.com/images?hl=en&source=hp&q=7+pin+trailer+plug+diagram&um=1&ie=UTF-8&ei=Ao73SrK3KJDYtgP6l8gK&sa=X&oi=image_result_group&ct=title&resnum=1&ved=0CBMQsAQwAA

[oreo57]

Check,
Check,
Check,
 
All grounds,That always seems to be the failing point.

[AustinBoston]

GlennS,

Thanx for the great information. However, I failed to include some more information.

In between ohming the trailer connection and testing the truck connection I took apart the trailer plug and made sure all the connections were good.  The plug just pulled off so I don?t think the connections were good and tight.
I put it all back together and plugged it into the truck.  When I turned on the running lights everything seemed fine.  When I turned on the left blinker all the lights on the trailer blinked, even the running lights. The same thing happened when I tested the right blinker.
This made me nervous so I disconnected it and began the ohming of the trailer.

Is there any reason you can think of for something like that to happen?

Yes.  These are classic bad ground symptoms.

Austin

[wavery]

If it is a bad ground (which it could be), I would start with checking the ground wire on the TV side of the trailer wiring receptacle. 2nd, check for a good ground on the trailer plug (going to the trailer ground lug).


If it were a ground issue with the left T/s bulb socket, you would have had no response because there would be no chance of finding a complete (or partially complete) circuit.

What can happen is, when you turned on your left blinker, the T/S bulb may not have found a good ground so the electrical current flowed back through the system looking for ground. As it flows through the system, the only "ground" that it can find is by passing through all of the positive leads on the other bulbs and back through those leads to the TV where it finds enough continuity to light all of the bulbs on the trailer. However, when this happens, the lights usually respond very dimly (however, they may respond bighter on some vehicles).

If the lights were all responding brightly, it is more likely that you either have wires crossed or little feeder wires touching other pins inside the plug.

[Bartman]

I'm inclined to agree with wavery.
Either I put the plug back together wrong or there are wandering wires.

I'm all but positive that I put the plug back together right, I was using the schematic that came with the trailer and it matches what wavery posted.

So now I'm down to the wandering wires.

I haven't found a grounding lug up by the hitch so I'll have to crawl under her to look.

Great posts though.

[wavery]

I'm inclined to agree with wavery.
Either I put the plug back together wrong or there are wandering wires.

I'm all but positive that I put the plug back together right, I was using the schematic that came with the trailer and it matches what wavery posted.

So now I'm down to the wandering wires.

I haven't found a grounding lug up by the hitch so I'll have to crawl under her to look.

Great posts though.

The grounding lug on my 2002 Coleman was under the forward part of the frame, just behind the tongue and just below the inverter.

When I checked mine, it was rusty. I pulled the wires out of it, wire brushed it, cut the ends of the wires of, removed any insulation and reinstalled them. I tightened the screw real hard then smeared it with dielectric grease, to cut down on corrosion.

[AustinBoston]

If it were a ground issue with the left T/s bulb socket, you would have had no response

Technicality - if there were no ground, this is true.  If it were a poor ground, it would seem to work, but would interfere with other lights using the same ground.  That's why (and I see this often on the juryrigged trailers around here) the turn signal will make the running lights blink the opposite way (i.e. the running lights go dimmer when the turn signal or brake light goes on, and brighter when the t/s goes off).  Note that the OP described something very similar to this condition above.

Austin

[Bartman]

OK, I did some more testing using a live battery and checked the grounds on both. Everything checked out good.
I started looking at the plug and it was showing signs of fatigue and/or damage.

I replaced the plug being careful to trim off any wild wire strands and everything works as it should now.

I can only conclude that there were wild wire strands running around in the plug. I used the pictures that came with the trailer to rewire the plug both times.

All is well though and many thanx to all of you for you advice.

[wavery]

Glad that you resolved your issue. Electrical problems can sometimes be very difficult to trace down. I have found that a lot of wiring issues are right there in the plug.

For future reference. It's a good idea to solder the ends of the wire leads before you put them in the connector (that's called "Tinning"). It helps to keep those little strands in there place and also provides a better connection when the screw is tightened down on the wire end. A little dab of dielectric grease and you are protected from corrosion for a long time.

[coach]

I see insulated ring terminals used on each wire.
Makes for a nice assembly

[AustinBoston]

Glad that you resolved your issue. Electrical problems can sometimes be very difficult to trace down. I have found that a lot of wiring issues are right there in the plug.

For future reference. It's a good idea to solder the ends of the wire leads before you put them in the connector (that's called "Tinning"). It helps to keep those little strands in there place and also provides a better connection when the screw is tightened down on the wire end. A little dab of dielectric grease and you are protected from corrosion for a long time.

Tinning also reduces corrosion, which causes it's own special set of problems.

Austin