Trailer wiring problems (7 pin coach side)

[JimCasazze]

Hooked up the toad yesterday and found that I have electrical gremlins in my trailer wiring.

Earlier this year, I replaced a little black box I found that converted the coaches independent turn signals, brakes and tail lights (3 bulb system) into the toad's two bulb system.  All worked fine for our six month trip

Today, when I tested the lights I found that pressing the brake would cause the coach turn signals to turn on (at all locations, not just the rear).  Also, no lights on the toad.  Suspecting that black box again, I cut it out.  This stopped all issues with the coaches brakes, turn signals, etc.  I bought a new box (supposedly a better product) and attempted to re-install.  However, while attempting to determine which wires are the turn, break and tail. I found that a) I have very low voltage on the hookup wires (8 volts or so) and b) turning on the directionals, causes more than one wire to pulse with voltage.

I believe of the 7 wires, is should have (1) break, (1) tail, (1) left signal, (1) right signal, (1) ground, (1) 12v always hot and (1) that is not in use.

To begin, I can not find a ground when testing each of these for continuity to the chassis.  I can find a tail and a break, but the signals seem to effect them when turned on.   In additional all voltages are low (8-10 volts).

The coaches break and turn signals work fine and are very bright.  It appears this is somewhere after the coach lights that the problem starts.  Does anyone know where to look?  Is there a harness somewhere that may need to be cleaned?  Any other thoughts?  Fuses?  Relays?

'99 Pat Thunder

Thanks
J

[Gerald Farris]

Jim,
You are not totally correct if you are talking about the wires at the 7 pin plug at the rear of the coach. Since the 7 pin connector is after the duplex adapter box the wiring at the 7 pin connector is 1. ground 2. tail 3. right brake 4. left brake 5. 12V hot 6. electric brake, and 7. back-up lights (rarely used). Here is a link to their positions on the connector; http://www.listatrailer.com/help/7wire.html

Gerald

[Steve Huber Co-Admin]

Jim,
Sounds like you've got a faulty ground between the coach and the toad or to/from the black box. I'd start by cleaning all the connectors. Radio Shack sells a fairly effective spray on contact and switch cleaner, but you should be able to get one at any electronics store. Home Depot may carry one also. Use an ohm meter to check to see that you have a ground connection between the gnd pin on the coach and coach chassis. Then check same between toad and pin and toad chassis. This should indicate where problem lies. If both coach and toad lighting systems work normally. problem has to be in connection wiring.

The conventional connections on a 7 pin connector are:
(Viewing the blade side and starting with the blade to your right of the key)
TM: tail light (brown wire)
LT: Left turn (yellow wire)
GD: Ground (white wire)
EB: Electric brakes (blue wire)
RT: Right turn (green wire)
AX: Battery (black wire)
Center: Spare (can be used for aux. braking system signal)

FYI; I installed the Blue Ox BX88267 brake/tail light system on both my toads and have been very pleased with the outcome. It consists of a wiring harness and tail/brake lights that you install in your existing tail light assemblies. The  system does not hook into or rely on the toad's electrical wiring or ground and is simply an extension of the coach's brake and tail light circuit. I just checked the Blue Ox site and see that they've upgraded from incandescent to LED lights. It protects the toad's lighting system (no more blown fuses, etc).

Good luck, Steve

[Steve Huber Co-Admin]

Jim,
I hadn't noticed Gerald's post before posting mine. The wiring is the same except that my list looks at the connector from the blade rather than the connection side.
Sorry for any confusion.
Steve

[JimCasazze]

Gerald,
I'm not sure I am understanding your reply.  What do you mean when you say "duplex adapter box"?  Are you referring to the little black box I replaced which does the 3 light to 2 light conversion?  If so, then my problem is before that.  If you are indicating there may be another box a "duplex adapter" as you call it, then where is it and what is it's purpose?  

Since my "black box" has now been removed, I am dealing with 7 wires that come from a wire harness under the frame at the very rear.  There are 5 white, 1 red, 1 black (maybe dark blue?)  This is before the 7 pin coach receptacle.  Clearly someone previous to me has been in here before, so that may make this even more difficult.

I am testing the wires right there.  They have all been cut free from the 7 pin coach receptacle as to find out exactly what is going on.  As I mentioned, I don't see any of them as ground when testing for continuity.  That is my first thought on something to track down, but the fact that 2 other wires seem to be shorted and since my voltages are all low, I'm now hoping that duplex adapter is something I haven't found yet, and the culprit.

Thanks for your help

PS Steve - thank's but this problem is ahead of the toad.  It isn't even connected.  Something on the coach side.

J

[Gerald Farris]

Jim,
What you are referring to as black box is the same thing that I referred to as the duplex adapter. If you do not find a good ground in the wires that were going to the 7 pin connector on your coach, no problem, just run another wire from a good clean ground on the coach frame to the ground terminal in your connector. You need three inputs (1 stoplight, 1 left turnsignal, and 1 right turnsignal)  to your "black box", and two outputs  (right stoplight and left stoplight) that go to the 7 pin connector. The fourth wire needed to your 7 pin connector is the tailight input.
 
If you have a bad connection that is causing low voltage to all wires going to the 7 pin connector (very unlikely), it will probably be easier to just tie into the needed inputs at the coach stop/tailights, than to trace and repair the factory wiring. If the problem is in the factory wiring, it is probably a corroded harness connector caused by moisture in the LF electrical bay. The most common reason for low voltage readings on all wires in a harness when there are multiple input sources, is a meter error that is usually caused by a bad ground.

If this is as clear as mud, just call me and i can walk you through the needed repairs. One word of caution, if you want permanet repairs, solder the wire connections that you make instead of using Scotch-Locks or just fwisting and taping the wires.

Gerald  

[JimCasazze]

Gerald,

I now understand the black box/duplexer is one in the same.  In my case this box is currently removed.  So I am working directly with the 7 (4 of importance) wires coming from the chassis wire loom.  I get low voltage on all turn signals, brake and tail lights.  I am using a alligator clip to the chassis for ground and get 12v from other sources, so I know the ground is good.  The lights are grounded to chassis right?  Maybe I should ground right to the battery to see if any different result?

You mention the factory wiring has a harness connector in the electric bay.  I will check there in the morning.  Any idea which one?  How I wish I had the wiring diagram for this coach!   Did they actually run the trailer harness all the way from the electric bay?  I would have thought it was spliced into the break/tail lights at the rear.   I'd have to agree a connector is very likely to be the problem here unless the wire harness itself somehow got pinched/damaged.

Thanks

J

[Tom and Pam Brown]

Check the plugs and pigtail.  Mine vibrated loose and had to use Loctite to keep from loosening.

[Edward Buker]

Jim,

If you ground the meter to the battery post and all the measurements stay about the same then your ground to the chassis that you are using for your meter is good at the rear of the coach. You have not told us that you have measured the chassis battery voltage to see what that is.After you get that measurement start the engine and take the same tail light wiring measurements and see what they are which is the real life condition that you will travel with. You could add a good clean ground wire connection from the frame as Gerald suggested along with the current ground feed to assure a good ground system is in tact. It is unlikely that the low voltage is caused by a connector given all the circuits feeds are low. That is most likely related to battery voltage, a bad ground, or normal harness voltage drop given the length of the leads and the load of all the lights that are already powered on.

As an aside I have a third brake light blinking circuit on my toad that simply will not activate until I start the RV engine and get enough voltage to the toad through the harness. If someone has increased the wattage of the tail light bulbs in the coach to brighten them that could be pulling more current and lowering the voltage to the coupler harness also. I would expect 11V + at these wire locations with the engine running, hopefully 12V+. There is a lot of wire involved here in the harness from the brake pedal switch or turn signal to the rear of the coach which will drop voltage with the load of the lights being on.

Later Ed