(Late, but I hope not too late) MY CONTROLLER DOES NOT SEE MY TRAILER...
As in brake controller, yes.
Little known but true - you can't test the output of a brake controller with only a digital meter.
THIS IS WHY:
The blue brake power wire will send out a constant low-ampere twelve volt signal to test continuity. This signal is likely to be in the milliwatt range, but will read twelve volts on a digital volt meter, as if the dratted thing is sending power to the brakes at all times....
Well, yes it is!
This is called a "test voltage"
But it doesn't have much power in that signal, it is used to sense whether or not there is a good connection OUT TO the brakes, and back through the frame and wiring grounds. It isn't enough to even BEGIN to activate the brakes - that takes a lot more current. All this does is ensure good connections. SO - if there is anything at all like a poor or corroded connection, there will be resistance in the circuit high enough to produce a bothersome "WHERE THE HECK IS THE LIGHT?" error....
Let me see if I can explain that a little bit more clearly: A milliwatt (or a milliamp for that matter) is a very small trickle of power, even if it is at twelve volts. VOLTS are best thought of as pressure, and current is best thought of as FLOW. If I have twelve pounds of pressure in a water pipe, but it's a small diameter of pipe - the pressure will be the same but only a small amount of water can go through it. Electricity works the same way.
Twelve volts, at one millionth of an AMP - is twelve milliwatts.
Now - if I slam on the "OH DOGGONE IT!" switch and let twenty or so AMPS at twelve VOLTS go through the wire, we have twelve times twenty or 240 WATTS (not milliwatts!) going to the brakes. In milliwatt terms - that would be 240,000 milliwatts.
BIG difference, isn't it?
It is entirely reasonable that enough AMPS at 12V will go through the wiring when the controller is activated to run the brakes, since higher amperes will overcome a slight amount of resistance from a rusty ground point, carbon or dirt in a connector, and so on.
But it's a HECKKUVVA clue to go through all of your ground tie-points on the trailer and the truck to make sure everything is clean, there are no damaged wires, and the connectors butt together right. Check the blue wires for damage too - for a complete electrical path to exist, there must be a path for power to go from the source, out to whatever is being powered, and back to the source through the ground circuit.
It has been a truism of trailers and RV's ever since the very first one went down the road that 99% of trailer electrical problems are caused by BAD GROUNDING.
If you have to run a new ground from the frame of the truck to the seven-way, or a new ground connection from the trailer frame to the trailer side of the seven-way (or flat-plug, etc...). Go right ahead and do it! If there is any DOUBT, do it. If it only means undoing a self tapping screw under the ground attaching point, cleaning away rust, and fastening it back down - DO IT!
It isn't that tuff.
WARNING: NEVER paint those connections after they are made, you will instantly insulate the whole works, and voltage can't flow through it. Paint seeps into cracks and crevices - the worst offender of all is Urethane Varnish, which is PLASTIC in a spray form.
You can paint an area where a ground screw is to be attached FIRST, and THEN run the screw into the hole. The screw will cut away any surface coating (we hope) and make a new contact. Don't install the screw if the paint is at all wet.
TEST FOR CONTINUITY with a digital meter.
Go from the ground connection in the plug, to a solid frame ground. If you can't find a near ZERO OHM path, the problem may still exist. You need less than one ohm from the connector to the frame of both the truck and the trailer for everything to work.
*With apologies to trippinbillies for not watching my E-mail closer. I see PM's at FTE right away, but a month of sundays can go by before I look on GMAIL.
Great Thread.
And I too have found that the "ground" or negitive continuity is often the source of electrical malfunctions. When ever practicable, I prefer to run a ground conductor wire, instead of relying just on the frame. However, the frame should still be atached (bonded) to the ground wire at some point(s). This leads me to my next point;
I'm not too sure I agree with this statement:
" WARNING : NEVER paint those connections after they are made, you will instantly insulate the whole works, and voltage can't flow through it. Paint seeps into cracks and crevices - the worst offender of all is Urethane Varnish, which is PLASTIC in a spray form.
You can paint an area where a ground screw is to be attached FIRST, and THEN run the screw into the hole. The screw will cut away any surface coating (we hope) and make a new contact. Don't install the screw if the paint is at all wet. "
Actually, I believe the exact opposite to be true. In an electrical connection the joined surfaces need to be clean bare metal to metal, and all parts of the connection need to be tight. Current doesn't flow through "cracks and crevices" of the connection. In fact, only moisture and contaminents which can (will) cause corrosion will get in the cracks. A good coat of paint or other sealent is a good thing. (AFTER the connection is made, NOT before)
IMHO, Rob.
Spray your negative battery post with clear polyurethane, and let us know what happens, okay?
It will be a good experience for you.
It may cause a lot of trouble, but it will be a learning experience.
You won't doubt me twice.
Sorry, I didn't think we were talking about battery terminals. (that's a different animal all together) I thought we were talking about the connection of the ground wire to the frame (from the connector plug, both at the tow vehicle and the trailer).
The basis of a good electrical connection is a clean and tight metal to metal contact. Preferably sealed to keep out anything that would cause corrosion down the line.
In the case of a ring terminal connector attached to a painted or rusty frame, I recommend that the frame mounting surface be cleaned to bare metal so that the ring terminal surface mates with a good conductive surface and does not rely only on the screw for conductivity.
A self drilling-self tapping screw in a fresh location on a painted or rusty frame might get you by for a while, but that same screw in the old hole or a machine screw connection on anything but clean bare metal is bound to fail (sooner than later).
I believe that it is marginal connections in the first place (often in the ground) that always has us going back to check and/or correct them.
I also believe that sealing out moisture and other contaminants that will cause corrosion in the connection (after it is made) is wise. A misting of paint or other appropriate sealer will prolong the joint. Now I can't speak for clear Polyurethane spray, as I don't know it's properties (and I don't know of one that would be recommended for this environment). But unless it has the ability to force it's way between to tightly mated metal surfaces and separate them (and perhaps it does)(?), I don't know how it could hurt conductivity. (NOTE: I am NOT recommending the use of Ployurethane on electrical connections.) Electricity does not flow well across cracks or gaps (at least not at 12 volts). Those little electrons have to be in pretty close proximity to each other in order for them to jump from atom to atom with ease. Therefor, sealing the cracks and gaps to prevent corrosion should not hinder conductivity.
As for your recommendation that I spray my battery terminals with clear polyurethane, I believe I'll pass. That's a learning experience I'd prefer to leave up to others.
I suspect that you may have had or witnessed this "good experience" with something less than the desired results. If so, Please tell us what happened.
Just a WAG, but if one did spray there battery terminals with Polyurethane and did not like the outcome, perhaps one or more of the below factors contributed to the unsatisfactory results.
As I stated earlier, Battery terminals are quite a bit different than most other electrical connections on our vehicles. Often located in the engine compartment, they are exposed to large variations in temps. They have to conduct very large currents, and (perhaps most relevant to the spray issue above) have a very large surface contact area at a low PSI between the mating surfaces (relative to other types of connections). Low PSI because for a given amount of rotational torque applied to the fastener, the clamping force is applied over the entire contact surface area. That battery terminal has a big surface area compared to a screw or bolt, and therefor does not have nearly as much clamping force along the contact area.
Greywolf, I have read, learned from, and enjoyed many,many of your posts over the years.All very informative and thought provoking. The above is just my opinion, on a small point, of yet another excelent thread. Keep it up.
RE; "You won"t doubt me twice", I sure hope not!
(Oops, I think I just did.)
The same is true of ground connections on the frame as on the negative battery post.
I thought as you once - and decided to completely eliminate battery acid or any other fluid caused corrosion on my battery terminals by sealing them up good!
Sounds perfectly logical so far, doesn't it?
What I didn't count on was the properties of aerosol spray cans and their contents.
SPECIFICALLY: If WD-40, PD-680, PB Blaster, and others - can percolate into, surround, and loosen the threads of stuck fast nuts and bolts - what do you suppose a substance with insulating qualities can do in an aerosol base?
The term PENETRATING FLUID applies here...
My test experience was in 1977. I spotlessly cleaned a battery post, checked it, made sure the engine cranked (which it did with no trouble at all).
Then I decided to keep it that way, and sprayed the terminals.
The marker lights wouldn't even come on, until I cleaned all that stuff back off...
It was instant. Total saturation and insulation within seconds.
So -YOU DO WHAT YOU WANT! But I hope I've at least given you food for thought.
In addition - MILITARY CORROSION CONTROL MANUALS AND DOCTRINE for Shipboard, Aircraft, and Ground Vehicles specifically state that paint must not be used on such connections.
All of which is the direct result of real-world experience and testing.
Again, do what you want. DON'T BLAME ME, I tried to tell you better.
I WILL say that a light misting might be got away with - if it doesn't run.
On battery clamps - the lead clamps (NO - this was not a "Side Post") are soft, somewhat malleable, and the idea is that the bolt on them will so squeeze them as to cause them to conform as much as possible to the post surface. Sometimes brass or copper is used for these, and for the same reason.
You would think that two soft metals clamped in this way would form at least some "EXCLUSION ZONES" that were so tight as to be as good as soldered. No airspace, no water space.
This forum is owned and operated by Internet Brands, Inc., a Delaware corporation. It is not authorized or endorsed by the Ford Motor Company and is not affiliated with the Ford Motor Company or its related companies in any way. FordŽ is a registered trademark of the Ford Motor Company.
