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View Full Version : Parasitic draw in horse trailers



JSwan
Jun. 14, 2010, 04:51 PM
Hopefully someone here can give me some suggestions.

Something on the horse trailer is draining the battery on the truck when I turn the lights on or press on the brakes.

Battery and alternator on the truck were replaced due to advanced age. I figured that was what was causing the problem. Nope. (voltage regulator is contained in the alternator)

I tested the brake controller and plug with the voltmeter - also hooked up the truck to my friends trailer - it's A-OK. No sign of arcing on the plug tines. Battery stays charged.

That leaves the trailer.

The draw occurs when I turn the lights on, and draws down very quickly when the brakes are applied. When I turn the lights off, the gauge returns to 14 volts. Lights on, drops to 12 immediately, then slowly drops below 12. With or without the lights, when brakes are applied it drops to 12 volts and continues to descend. I've not allowed the battery to drain completely of course. Regardless; when the trailer is in use the battery is supplying a lot of the current and the alternator cannot recharge it quickly enough.

When I release the brakes/and or turn the lights off, the alternator quickly recharges the battery.

I don't have a wiring diagram of the trailer. I thought perhaps the replaced alternator was undersized; but I checked the specs on the truck and it seems the alternator is the correct one. (I didn't do the work)

Ok electrical experts - where do I start looking and what am I looking for?

Thanks.

eta: I've towed that trailer with this truck for many years; this is the first time I've had an electrical problem with either.

Chardavej
Jun. 14, 2010, 04:56 PM
When I read the title I thought "Worms being drawn to horse trailers?"

Sorry, I have no help, but good luck! That is frustrating.

Catersun
Jun. 14, 2010, 05:11 PM
sounds like there is a short in the trailer wiring.... I think I'd rather stick needles in my eyes than try and diagnos where though.... I don't even know where to suggest you start looking.

any chance it does the same thing when hooked up to a different rig?

how old is the trailer/wiring? At some point the insulation breaks down or wears off and you just have loss. Sounds like your juice is leaking out somewhere.

sublimequine
Jun. 14, 2010, 05:15 PM
When I read the title I thought "Worms being drawn to horse trailers?"

Sorry, I have no help, but good luck! That is frustrating.

I thought, "Oh, people who are constantly bumming trailer rides off of others, like parasites?" :lol:

Alagirl
Jun. 14, 2010, 05:56 PM
sounds like there is a short in the trailer wiring.... I think I'd rather stick needles in my eyes than try and diagnos where though.... I don't even know where to suggest you start looking.

any chance it does the same thing when hooked up to a different rig?

how old is the trailer/wiring? At some point the insulation breaks down or wears off and you just have loss. Sounds like your juice is leaking out somewhere.

somewhere the wireharness sprung a leak.

rugbygirl
Jun. 14, 2010, 06:10 PM
My guess is also a short, or possible a loose connection. As with the others, you couldn't pay me enough to diagnose that again.

Usual suspects are the wiring along the truck chassis, where general wear and tear can eat through the coating, as well as points where the wire rests on a sharp point (like the edge of a piece of steel)

If it's in the trailer itself, that's usually tougher, especially with no circuit diagram...

Sounds like you know a thing or two about this, but time to take each wire and test it, then do each in combination, lights on, lights off, etc. If you don't have a decent multimeter, don't bother though, pay money to have someone else beat their heads against a wall :D

Equibrit
Jun. 14, 2010, 06:57 PM
A Treatise on the Importance of Smoke - by Joseph Lucas

All electrical components and wiring harnesses depend on proper
circuit functioning, which is the transmission of charged ions by
retention of the visible spectral manifestation known as "smoke".
Smoke is the thing that makes electrical circuits work. Don't be
fooled by scientists and engineers talking about excited electrons
and the like. Smoke is the key to all things electrical

We know this to be true because every time one lets the smoke out of
an electrical circuit, it stops working. This can be verified
repeatedly through empirical testing. For example, if one places a
large copper bar across the terminals of a battery, prodigious
quantities of smoke are liberated and the battery shortly ceases to
function. In addition, if one observes smoke escaping from an
electrical component such as a Lucas voltage regulator, it will also
be observed that the component no longer functions.

The logic is elementary and inescapable! The function of the wiring
harness is to conduct the smoke from one device to another. When the
wiring harness springs a leak and lets all the smoke out of the
system, nothing works right afterward.

Starter motors were considered unsuitable for British motorcycles for
some time largely because they regularly released large quantities of
smoke from the electrical system.

It has been reported that Lucas electrical components are possibly
more prone to electrical leakage than their Bosch, Japanese or
American counterparts. Experts point out that this is because Lucas
is British, and all things British leak. British engines leak oil,
British shock absorbers, hydraulic forks, and disk brake systems leak
fluid, British tires leak air and British Intelligence leaks national
defense secrets.

Therefore, it follows that British electrical systems must leak
smoke. Once again, the logic is clear and inescapable.

Sometimes you may miss the component releasing the smoke that makes
your electrical system function correctly, but if you sniff around
you can often find the faulty component by the undeniable and
telltale smoke smell. Sometimes this is a better indicator than
standard electrical tests performed with a volt-ohm meter.

In conclusion, the basic concept of transmission of electrical energy
in the form of smoke provides a clear and logical explanation of the
mysteries of electrical components and why they fail.

"A gentleman does not motor about after dark." - Joeseph Lucas, 1842-
1903


PS - checked for ants in the plug ? (the smoke attracts them)

cssutton
Jun. 14, 2010, 07:22 PM
I don't believe that it is the trailer wiring.

Reason being: The lighting circuit and the brake circuit are two entirely different circuits.

So if the truck is OK, apparently proved by hooking to your friend's trailer, it is something to do with the trailer.

But for it to be bad wiring, it would have to mean that both the light wiring and the trailer wiring went bad at the same moment, which is not really that likely.

I would very carefully examine the trailer plug or connection, as there is very likely a short or a bad connection in the plug itself.

It sounds like both the lights and brakes are grounded in the plug. If that is the case, what is happening is that as you send power to either, you have a short.

The very latest trucks have fuse protection on each circuit and you would get a blown fuse.

Apparently you have an older truck. That is not bad, it just means that you must fix the problem because you have no overload protection.

CSSJR

Alagirl
Jun. 14, 2010, 07:28 PM
A Treatise on the Importance of Smoke - by Joseph Lucas

All electrical components and wiring harnesses depend on proper
circuit functioning, which is the transmission of charged ions by
retention of the visible spectral manifestation known as "smoke".
Smoke is the thing that makes electrical circuits work. Don't be
fooled by scientists and engineers talking about excited electrons
and the like. Smoke is the key to all things electrical

We know this to be true because every time one lets the smoke out of
an electrical circuit, it stops working. This can be verified
repeatedly through empirical testing. For example, if one places a
large copper bar across the terminals of a battery, prodigious
quantities of smoke are liberated and the battery shortly ceases to
function. In addition, if one observes smoke escaping from an
electrical component such as a Lucas voltage regulator, it will also
be observed that the component no longer functions.

The logic is elementary and inescapable! The function of the wiring
harness is to conduct the smoke from one device to another. When the
wiring harness springs a leak and lets all the smoke out of the
system, nothing works right afterward.

Starter motors were considered unsuitable for British motorcycles for
some time largely because they regularly released large quantities of
smoke from the electrical system.

It has been reported that Lucas electrical components are possibly
more prone to electrical leakage than their Bosch, Japanese or
American counterparts. Experts point out that this is because Lucas
is British, and all things British leak. British engines leak oil,
British shock absorbers, hydraulic forks, and disk brake systems leak
fluid, British tires leak air and British Intelligence leaks national
defense secrets.

Therefore, it follows that British electrical systems must leak
smoke. Once again, the logic is clear and inescapable.

Sometimes you may miss the component releasing the smoke that makes
your electrical system function correctly, but if you sniff around
you can often find the faulty component by the undeniable and
telltale smoke smell. Sometimes this is a better indicator than
standard electrical tests performed with a volt-ohm meter.

In conclusion, the basic concept of transmission of electrical energy
in the form of smoke provides a clear and logical explanation of the
mysteries of electrical components and why they fail.

"A gentleman does not motor about after dark." - Joeseph Lucas, 1842-
1903


:lol::lol::lol::lol:

JSwan
Jun. 14, 2010, 08:21 PM
Oh geez thanks, guys. All y'all are sooooooo helpful. :lol::lol:


csutton- I was thinking the same thing. Lights and brakes? They're separate. Yes, both utilize the plug for ground; accessories in the middle - typical layout for a trailer. Both the truck and trailer are a little over 10 years old.

I admit I had not examined the plug carefully. That does seem to be more likely than both the brake and lights wiring going bad at the same time.

Though with my luck....

After reading your post I did try to examine it and test it with the multimeter but the light was failing so I couldn't see well. The inside of the plug does look like it's seen better days. The readings were all over the place - but I was slapping at mosquitoes so that may be why.

Thanks everyone for your help (and jokes).

cssutton
Jun. 14, 2010, 08:23 PM
By the way, do you know how to check the circuits for a short?

http://www.ladyada.net/library/metertut/continuity.html

If you put one probe into the trailer plug at the light position and the other probe on the frame, you can determine whether that wire is shorted because you will get a reading demonstrating continuity.In other words, the reading will be the same as it would be if you put the probe on each end of a long wire.

No reading means no continuity = no short.

Be that as it may, the pug itself is suspect.

CSSJR.

cssutton
Jun. 14, 2010, 08:24 PM
OK.

I see that you do.

I was writing as you were posting, so I was late to the party.

JSwan
Jun. 14, 2010, 08:41 PM
csutton - no, I don't know very much at all and my helper is not available for the week. Which is why I posted here; I know you, Tom King, Frank B and a few others might have some ideas. I'm just not that experienced or confident about troubleshooting electrical problems. And I've got no experience with odd electrical problems with trailers.

So your link is great and I will be sure to use it.

Thanks.

cssutton
Jun. 14, 2010, 08:51 PM
I doubt that you even need to test.

I suspect something simple like plugging up and unplugging so many times that the insulation is worn close to the plug and is shorting.

Or maybe someing like dirt in the plug causing a weak short.

But think of the testing this way. Assume you are testing a switch. With the switch in the off position, the probes put on the contacts will read zero.

With the switch in the on postion, the probs will show that current is passing from one probe to the other.

So a short would read the same as switch on and no short would read the same as switch off.

Testing the trailer using the above is simple.

DO NOT test the truck wiring this way. Much more complicated.

Anyhow, your test with the other trailer seems to give the truck a clean bill.

CSSJR

Catersun
Jun. 14, 2010, 09:36 PM
you can use a small emery board to clean your plug connections, it's a PITA, but if it is in the trailer it's somewhere before it splits which suggests the plug. We went through this with my trailer before we moved the horses home.

AdAblurr02
Jun. 15, 2010, 12:14 AM
New plug ends for the trailer pigtail are cheap and easy. I would guess that if you crack yours open and take a peek, you will find corrosion. Typically, it's in the area between the (permanently) hot lead and the ground - the battery charging circuit from truck to trailer is "supposed" to be hot all the time, and often if a rig is left hitched, it will start building corrosion.

I've had to rewire EVERY trailer we have ever owned, and plugs are the place to start looking. Hint - when you replace it, before final reassembly coat the terminals liberally with dielectric grease (vaseline will substitute) to help keep moisture and corrosion from starting again - at least, for a while :) Second hint - buy the plugs at a parts store, NOT cheepy box store crapola. Get brand name parts, they really are better!

AnotherRound
Jun. 15, 2010, 02:50 PM
I don't believe that it is the trailer wiring.

Reason being: The lighting circuit and the brake circuit are two entirely different circuits.

So if the truck is OK, apparently proved by hooking to your friend's trailer, it is something to do with the trailer.

But for it to be bad wiring, it would have to mean that both the light wiring and the trailer wiring went bad at the same moment, which is not really that likely.

I would very carefully examine the trailer plug or connection, as there is very likely a short or a bad connection in the plug itself.

It sounds like both the lights and brakes are grounded in the plug. If that is the case, what is happening is that as you send power to either, you have a short.

The very latest trucks have fuse protection on each circuit and you would get a blown fuse.

Apparently you have an older truck. That is not bad, it just means that you must fix the problem because you have no overload protection.

CSSJR

I think this is where you start. If as CSS says these are two separate circuits, then the only way you experience your problem from either circuit must be at the spot which interacts with both circuits. I would start with replacing the plug. HOpefully, this is all it is.

AnotherRound
Jun. 15, 2010, 02:58 PM
Boy, wouldn't this be a good Puzzler for the NPR auto repair guys, Mariozzi brothers, etc.

Describe the problem just as the OP did, then ask "Where's the short?" Very cool.

2bee
Jun. 15, 2010, 04:15 PM
Plug has already been mentioned. Check in, on, around your tail/brake light socket bulbs and wiring.

Side note; if you do have one of the screw terminal plugs, I always replace those with a sealed one piece cord/cable. Some butt connectors and shrink tube will give years of reliable service. See this (http://cgi.ebay.com/ebaymotors/ws/http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=120435405261&viewitem=). Notice this one has contacts on both side of the pin slot, much more reliable electrical connection.

2bee
Jun. 17, 2010, 07:26 PM
Get 'er fixed?

JSwan
Jun. 17, 2010, 07:43 PM
I sheepishly admit that I said the hell with this crap and took it to the repair guy up the road. I am pretty sure it's the plug.

Guess it's a sign I'm getting older. There was a time when I'd not have hired someone for something like this. I'm just tired of fixing all this equipment. I still have to fix the bushhog and the pump on the sprayer.

But I really appreciate the effort everyone put it to try and help me figure out what it was.

Alagirl
Jun. 17, 2010, 08:25 PM
I sheepishly admit that I said the hell with this crap and took it to the repair guy up the road. I am pretty sure it's the plug.

Guess it's a sign I'm getting older. There was a time when I'd not have hired someone for something like this. I'm just tired of fixing all this equipment. I still have to fix the bushhog and the pump on the sprayer.

But I really appreciate the effort everyone put it to try and help me figure out what it was.

I don't blame you one bit!

It might be just the plug, relative easy fix, but it could also be a weak spot down the harness...you spend a lot of time tracking that down, time you can spend better, with less frustration fixing the bush hog and the sprayer! :lol:

Ghazzu
Jun. 17, 2010, 08:28 PM
Hey, I went to pick up my trailer yesterday after leaving it for some repair work, including some wiring issues.
Took the guy a good half-hour to figure out why the left turn signal wasn't working after we hooked up to my truck--and he had all sorts of nifty diagnostic lights.
(Turned out that one of the wires changed color halfway from plug to tail light...)