OT - Trailer Wiring Problem

Of course the trailer lights stop working - I have to drag it 300 miles the day after tomorrow!
Specifically, what has stopped working is the driver's side blinker and brake light, which are on the same output of the flat-four plug on the van. After chasing the problem in the trailer's harness for longer than I shoud have, I finally figured out that the problem is in the van, not the trailer.
First, let me make it clear that the blinkers and brake lights on the van itself work fine. The problem exists somewhere in the wiring for the flat-four plug.
The unloaded outputs at the flat-four sockets for the both trailer lights and the passenger side blinker/brake read ~12 volts, loaded they read ~11 volts. (I loaded it with a bare bulb, but I get the same readings with the trailer attached)
However, the unloaded output at the flat-four for the driver's side blinker/brake is ~7 volts, loaded it's zero. Once again, it was loaded with a bare bulb, so the trailer has nothing to do with the issue.
So, I know the problem is in the van's harness or the perhaps something with the pigtail, but I'm not sure what I should be looking for. The 2 feet or so of the pigtail that is exposed looks fine. After that it runs behind the trim into the bowels of the van. At first light, I guess I'm going to have to start pulling panels off. I took a quick look under the van (2004 Odessey) but it's late and dark, so I'll start again in the morning.
What could cause the voltage at one output of the flat-four to be down by half and what would cause it to drop to zero under the load of a single trailer bulb?
Thanks for any suggestions.
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DerbyDad03 wrote:

At the same time you are measuring 7 volts on the driver's blinker/brake "bare bulb" is the van's blinker/brake lamp noticeably dimmer than when the "bare bulb" is not connected?
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There is no noticeable difference in the van's lights. On this model van, the brake and blinkers are not the same bulb like they are on the trailer. The van has separate amber blinkers, so the wiring to them is different than to the flat-four for the trailer - at some point, anyway.
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On Fri, 11 Jul 2008 22:02:23 -0700 (PDT), DerbyDad03

I should have asked about this.
This probalby changes some of my advice in the other post. ... Ugh. Worse than that. I made a mistake in my other post, not addressing the need to run two wires from the tail light connector, I'm sorry. See below.
While they sell some sort of adapter for people who put in their own trailer wiring, I'll bet it costs 10 or 15 dollars.
I hadn't noticed that my car is like yours with amber blinkers, and one can't just connect the blinker wire AND the brake wire to the same wire to the trailer. I think if you do that, later, when you put on the blinkers it will light the bulb on the other side two, because the brake bulbs are connected together, but I'm not sure. I only know you can't do it.
So I if you decide to run replacement wires from your current left rear lights, you have to do this also.
RAther than run around looking for that device, since I wasn't at my house, I went to Radio Shack and bought a bag of 2 diodes for a dollar and a half. I think they had 2 or 5 amp diodes, either of which is a lot more than the trailer lights use. I got the bigger ones. Because I can never keep track for sure of the meaning of plus and minus when it comes to diodes, I used an ohmmeter to verify which direction current would go through the wire, and then I put in one wire with those jumper wires to verify that I was right. Then I soldered the same end of both diodes to the pigtail, and the ohter end of the diodes to short pieces of wire, which I then stuck in the connector as described in my othe post. The same connector served both bulbs in my case, although it's conceivable that one bulb is in the fender and one bulb somewhere else, like the van door. I think I wrapped one layer of tape around the whole thing and then put back the fuzzy cardboard that goes over all this stuff inside the trunk just above the bumper.
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DerbyDad03 wrote:

In that case check the adapter box that converts the separate brake lights and turn signals to the standard American scheme. Some of them are crap and when they go bad all sorts of electrical weirdness can happen. Had a friend with a Jeep Cherokee with all sorts of weird issues; removing the trailer light adapter that a PO had installed solved all of them. I found it one night with the parking lights permanently on and the box smoking hot. (I guess it must have been tapped into an always hot 12V feed somewhere, so it was likely a poor installation from the beginning.)
nate
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If the other lights work, the fault is probably in the connector that connects the trailer wire to the vehicle's wire. They (installers) often use clamp on connectors that look like this
http://autolumination.com/images/auto_bulbs/quick_splice.jpg
It's hard to explain over the net, but you may have to strip some wire with a knife, and make a real connection instead of the crimp on splice.
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On Jul 13, 7:53am, "Stormin Mormon"

Did 'cha miss my post where I detailed the solution? It was posted about 9 hours before yours.
As far as the vampire clips you provided a link to, they weren't used in the original installation, and they weren't used as part of my repair. I don't think I've ever seen a connecteor more prone to failure than those. I'm surprised that "professionals" even use them.
On the other hand, maybe I'm not surprised. They're quick and easy and usually outlast the warranty, after which it's the consumer's problem to either repair or pay to have repaired.
I prefer the tap-soldering method shown towards the bottom of this page, although admittedly it takes a lot more time and can be tricky in confined or accessibility-challenged spaces.
http://www.mmxpress.com/technical/connections.htm
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Boden,
Thanks for the response, but you seem to have misunderstood the symptoms I described.
I am not measuring "7 volts on the driver's blinker/brake bare bulb".
As I said in my OP the *unloaded* voltage is 7 volts. Once I connect the bare bulb (or the trailer) the voltage drops to zero.
In any case, there is never any difference in the light output of the van's brake lights or blinkers. They work fine whether the bare bulb (or the trailer for that matter) are hooked up or not. For what it's worth, the van does not even use the same bulb for the brake and blinkers like the trailer does. The van has a separate, amber blinkers.
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On Fri, 11 Jul 2008 22:12:47 -0700 (PDT), DerbyDad03

Yeah. Maybe I would have been prepared with the diodes and even the wires soldered to them, but the instructions for my first trailer said only that SOME cars were wired differently. I didn't think that meant me, but when I looked at my car's lights I started to catch on. Still not sure, I looked on the web and there I found a page where the author said clearly that if you have amber blinkers (and not red blinkers) you need to make special provisions.
And he implied that if you had red blinkers, the same bulb would be used for brakes and turn signals. He's right, isn't he?
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On Fri, 11 Jul 2008 21:20:02 -0700 (PDT), DerbyDad03

How is there any voltage? Do you have the brakes on, or the blinker on, or both?

Who put in the trailer wiring? The factory, you, a shop? Where did they connect the wire to the trailer to the wires in the van?

I think that's what you have to do. If you have the shop manual for the van, and the wires were factory installed, maybe it would have the location of the connecting point. The Chrysler manual has separate pages from the wiring diagram pages, that show where devices are and where wire connections are.
If you're really out of ideas, or just to save time and effort, find the turn signal bulb at the left rear turn signal, follow it back to the connector, pull apart the connecter, cut the wire to the pigtail leaving as much as possible on the pigtail, strip it and stuff it in the connector. (You probably know all these details, but you can take the socket out, identify which is the brake filament and follow the the wire inside the bulb to the correct external wire, and ffollow that to the socket and identify the color of the wire. At least you can do this with 1157 bulbs. Is that still the bulb used in an Odyssey?) Well if you can't tell that way, you can tell with a voltmeter on the hot side of the connector you opened.
I just did that with a Chrysler. The side with only one wire went quickly, but the side with two wires was sort of hard to get right -- it crumpled back or displaced one of the two wires the first time or two. But you only have to do one wire, which I think is much easier.
Also I don't know how long mine will last. But they lasted 5 days to drive from Dallas to Baltimore. About 1100 miles iirc. I'm just being cautious, when I suggest it might not last. I put the trunk carpeting back over the connector and inn my experience things like this usually last 10 or 20 years.
The other possibility is to strip some of the insulation from the correct wire and solder in the pigtail wire, and tape it. Or for this trip you have to make, you could do the sort of thing I do, and use one of those 6 inch jumper wires from Radio Shack, 10 to a bag, 3 or 4 dollars a bag, with alligator clips on each end. No soldering required.
When the primary wire to my ignition coil from the ignition switch failed, somewhere above the engine, I used a two foot wire that I ran from a place I stripped fairly near the fire wall, just lying across the engine (avoiding the hot spots), to the primary, with alligator clips on both ends. The car ran that way for two years, without my even thinking about it again, and when I junked it for other reasons, I removed the jumper and put it back on my rack of jumper wires.
(The car had stalled 3 miles from my home, on a public street. I coasted to the curb and then got a ride home. I rode my bike back to the car the next day. This method of repair got me running in a half hour. I didn't want to spend hours on the street, and there was really no better way to do this, although at the time I sort of thought I was taking some sort of improper shortcut.)
NOt the extension with the DSL line, but I think some of my other extension phones have been connected with jumper wires for years now. I still haven't finished what I was doing to them.

If I ever knew, I can't remember now.

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- How is there any voltage? Do you have the brakes on, or the blinker on, or both?
Uh, yeah. How else would I measure the voltages? :-)
A piece of wood between the seat and the brake pedal applies the brakes. While I am not able to read the exact voltage when the blinkers are on since my VOM is not fast enough, I do see it flashing it's 0.L which means it is trying to read something. The flashing stops as soon as the bulb is attachedand it reads a constant zero. Since the brakes and blinker use the same output on the flat-four and the same filament, I'm assuming it's 7 volts when the blinker is on, just like the constant 7 when the brake is on.
Humor Break! Replace "people" with the nationality/gender/race/hair color of your choice...
Two people were working on the blinkers of their car. One guy was inside the car, the other was outside. The person inside asked "Are they working?" The person outside said "They're working...They're not working...They're working...They're not working...They're working..."

- Who put in the trailer wiring? The factory, you, a shop? Where did - they connect the wire to the trailer to the wires in the van?
The wiring was installed 2 years ago by a reputable trailer shop when I had the hitch installed. The lights have worked fine on this van for the full 2 years. I don't know where they connected the wires, all I see is the pigtail.
--- snip ---
re: your suggestions for tapping into the existing harness or connector.
First I have to find the connector in the van...and finish painting the fenders, put them back on the trailer, go to the dentist, drive 45 minutes to (and from) a graduation party, and get everything ready for the trip.
I'm towing the trailer 300 miles on Sunday, dropping it off and driving back without it - all in one day. There is a very good chance I'll be doing it with only 1 blinker.
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On Fri, 11 Jul 2008 22:33:32 -0700 (PDT), DerbyDad03

Well, that'a s possibility too. I was running late and when I saw that the my wiring needed more effort, I considered driving all the way to Baltimore with only the tail lights.
I don't think finding the connector would take long.
But consider asking in sci.electronics.repair, where think more about stuff like this, including many who have other interests as well and some work on cars.
But maybe emove almost all the narrative except for a description of the problem. There not as chatty as even the other people here.
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DerbyDad03 wrote:

(snip)
And I'll bet the connection is one or more of those crimp-on vampire taps, usually translucent blue in color. Even the good quality 3m ones are prone to failure. I'd start by replacing that, It probably isn't very far from where the pigtail vanishes into the bodywork. Also make sure that where the pigtail vanishes from sight, that the insulation hasn't been cut or pinched where it runs through the panel.
You have my sincere sympathies. BTDT a lot in my younger days, back when it seemed worth the effort to add stereos to cars and such. Chasing electrical demons in vehicles is one of the more annoying areas of electrical work.
-- aem sends...
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wrote:

- How is there any voltage? Do you have the brakes on, or the blinker on, or both?
Uh, yeah. How else would I measure the voltages? :-)
A piece of wood between the seat and the brake pedal applies the brakes. While I am not able to read the exact voltage when the blinkers are on since my VOM is not fast enough, I do see it flashing it's 0.L which means it is trying to read something. The flashing stops as soon as the bulb is attachedand it reads a constant zero. Since the brakes and blinker use the same output on the flat-four and the same filament, I'm assuming it's 7 volts when the blinker is on, just like the constant 7 when the brake is on.
Humor Break! Replace "people" with the nationality/gender/race/hair color of your choice...
Two people were working on the blinkers of their car. One guy was inside the car, the other was outside. The person inside asked "Are they working?" The person outside said "They're working...They're not working...They're working...They're not working...They're working..."

- Who put in the trailer wiring? The factory, you, a shop? Where did - they connect the wire to the trailer to the wires in the van?
The wiring was installed 2 years ago by a reputable trailer shop when I had the hitch installed. The lights have worked fine on this van for the full 2 years. I don't know where they connected the wires, all I see is the pigtail.
--- snip ---
re: your suggestions for tapping into the existing harness or connector.
First I have to find the connector in the van...and finish painting the fenders, put them back on the trailer, go to the dentist, drive 45 minutes to (and from) a graduation party, and get everything ready for the trip.
I'm towing the trailer 300 miles on Sunday, dropping it off and driving back without it - all in one day. There is a very good chance I'll be doing it with only 1 blinker.
The 7 volts indicates that you are probably using a digital voltmeter, which is a very poor device for troubleshooting. It responds to tiny leakage currents. You are not trying to accurately measure voltage, you are trying to detect the presence or absence of enough power to light the bulb. You have a disconnected, broken, loose, or corroded connection somewhere in your harness. Use a bulb connected to a sharp pin and to ground to trace the harness, piercing the insulation if needed. The problem may be in the connector itself and if so you may have to rig a temporary jumper across it. If you have the trailer wiring plugged into the vehicle harness, that plug and socket are also likely locations of a poor connection.
Don Young
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DerbyDad03 wrote:

It's a poor connection wherever the trailer plug connects to the vehicle harness. If the installer used a Scotch-Lok I would bet that that is where the problem is; the only kind that is acceptable to use is filled with silicone grease, the plain ones will eventually corrode and drive you nuts.
If it's an adapter that plugs in between the rear body harness and the rear light harness, simply remove it, clean the connections, pack with silicone grease and try again.
good luck
nate
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DerbyDad03 wrote:

I was helping a friend with similar issues. One light on the trailer did not work. I found the output voltage was half what it should be on the brake light. Turned out to be that the car had an electronic trailer wiring control module that was bad. The module was ~2" square box hidden under a panel in the rear trunk area. In my case there was also a bad wiring job on the trailer that probably toasted the module. The module was factory installed $tealer only item. There may be afte-rmarket controllers that could be wired in?
Kevin
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Kevin Wins!
Because my van has separate bulbs for the blinkers and brakes, the shop that installed the hitch also installed a "3-wire to 2 wire converter" - a ~2" square box hidden under a panel in the rear hatch area. As soon as I pulled the panel from which the pigtail emerged, there was the box. Even though it was an after-market install, the hitch shop used a harness with a connector that plugged into an existing connector in the van's harness.
The hitch shop was closed today so I called a Honda dealer to see if I could get a replacement module/pigtail, but all they carried was some type of "complete harness with brackets, modules, pigtails" etc. $170! That's about what I paid for the entire hitch and wiring, installed, a few years ago.
U-haul carries a compatible module/pigtail but with bare wires for $18, so I bought one, cut the module off of my old harness and used a Europa terminal strip so I could use the original connector and plug it directly into the van's harness.
http://dnn.hylecapl.com/Portals/3/RikoComponents/Europe.jpg
aem mentioned the "vampire clips". I hate them! The U-haul unit came with those types of clips and the guy behind the counter said "Make sure you don't lose the clips. You'll need 'em to connect the module to your harness." I told him I was going to throw them away as soon as I opened the package. Vampire clip is a great name for them because they *suck*!
All lights are working now and I'm off on my 600 round trip at 6AM.
Thanks for all the suggestions on where to look.
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