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Topic: Towing - one tail light on toad works, one does not  (Read 419 times) previous topic - next topic
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Towing - one tail light on toad works, one does not
A frustrating problem:  you rig your toad for travel only to discover that one tail light/signal/brake light on the toad works and one does not.  When not connected, all the toad lights work, but when connected to the LD, one side doesn't work.  (just for clarification)

I had this problem last year and looked everywhere for the problem.  I checked the tail light diodes, wiring, fuses...

The only thing I found wrong last year was the wiring connector on the toad side had become corroded.  I replaced the connector and was really frustrated when it still didn't work.  I fussed and poked about and finally, it worked again.  I really didn't know what I had done to fix the problem but it worked and I was happy.

Roll the clock forward to about 10 days ago.  We were all packed and ready to hit the road for Montana.  I hooked up the toad and the problem was back again.  Everything worked except the left rear tail light/turn signal/brake light on the toad.  I worked all that day trying to figure it out.  My test light showed that the left turn/tail lamp circuit would work for about two seconds and then the test lamp went very dim.  A circuit was there but the test lamp was very weak.  I suspected a short. 

On the second day, I got out the Ford E450 service manual that I carry for my model year.  In digging into the fuse and relay section, I found that there were two relays identified as left and right turn signals.  Hmmm.  I went to an auto parts store and bought new relays.  Bingo!  Problem solved.  I suspect that the left turn signal relay contacts were corroded or otherwise compromised and were completing a circuit, albeit a very high resistance circuit and thus the dim test lamp.  I suspect the reason I got it to work last year was because the relay contacts were not yet completely hosed and for reasons known only to gremlins, the relay worked again after an intermittent failure. 

So, if you ever encounter a bizarre problem such as this with your toad tail/signal lights where one works and the other doesn't, the turn signal relay(s) may be your problem.

I searched the web and others towing trailers have had this problem but they all went looking for diode and fuse problems.

I don't know if this has been addressed before as a technical issue here, but if it has, then I add my experience to the knowledge base to confirm the probable fix.

Dan
2007 IB-30
Re: Towing - one tail light on toad works, one does not
Reply #1 –
"...went to an auto parts store and bought new relays."

Noticed your use of the 'plural', as in two! Where are these relays located... I'm presuming it's under the dash?   ::)
Steve S.
Lazy Bones & Cedar
2004 30'IB (Island Bed)
Yesterday is History, Tomorrow is a Mystery
Live for the day!
Re: Towing - one tail light on toad works, one does not
Reply #3 –
Thanks for that link Ron. Good to know info there. Guessing it applies to my '04 also. Hope I never have need to find out.   :o
Steve S.
Lazy Bones & Cedar
2004 30'IB (Island Bed)
Yesterday is History, Tomorrow is a Mystery
Live for the day!
Re: Towing - one tail light on toad works, one does not
Reply #4 –
I've had a similar problem about 2 years ago with 3 different causes.  The first was a loose ground wire in the electrical cable connector.  The second issue was the male connection pins on the the towed vehicle had collapsed a bit and were not making a good contact.  I used a small flathead screw driver to spread the prongs.  And the 3rd was just dirty contacts.  So every 6 months or so I use electric contact cleaner with a Q-tip on both the ends of the cable and on both vehicle's connections.  Then I place a dab of dielectric grease on the cable connections.   Hope some of this helpful.
Re: Towing - one tail light on toad works, one does not
Reply #5 –
Quote from: Lazy Bones  - 
"...went to an auto parts store and bought new relays."

Noticed your use of the 'plural', as in two! Where are these relays located... I'm presuming it's under the dash?  ::)

No, these turn signal relays are located under the hood, above and just left of the fuse box - in my 2007.  I replaced both relays after I discovered the left signal relay was the culprit.

Dan
2007 IB-30
Re: Towing - one tail light on toad works, one does not
Reply #6 –
Dan,

Does this out of focus picture resemble the "relays" you replaced?
Don & Dorothy
Sold our LD in June of 2023

Our boring always non-PC travel blog
Traveling Dorothy
Re: Towing - one tail light on toad works, one does not
Reply #8 –
I had a similar problem that turned out to be something wrong with the connecting cable or the connectors on the cable. Each of the wires in the cable seemed to be tightened down just fine, but when connected to the vehicles, always one taillight was out. Actually, it was just really dim, but looked to be out. Using a different cable fixed the problem.

David G
2005 MB
 
Re: Towing - one tail light on toad works, one does not
Reply #9 –
I replaced the towing relays today. No change. I don't have a problem with the connector as I took it off. I get strange volt readings on the LD installed bare wires where the connector was. Like 3 volts on the left signal, 1 on the right, but 12 on the running. That eliminates a ground problem I would think. Looks like I am going to have to take it to a repair shop as this is over my head.
Don & Dorothy
Sold our LD in June of 2023

Our boring always non-PC travel blog
Traveling Dorothy
Re: Towing - one tail light on toad works, one does not
Reply #10 –
Don-

I would test at the relay and fuse sockets before I took it to someone else.

I can assist by phone, if that would help you. Just send a private message with your phone number and a few days and times convenient for me to call you.

Mark H
Former owner, 31-foot gas Class A
Former owner, 1997-8 mid-bath
Re: Towing - one tail light on toad works, one does not
Reply #11 –
Quote from: Don Malpas  - 
I replaced the towing relays today. No change. I don't have a problem with the connector as I took it off. I get strange volt readings on the LD installed bare wires where the connector was. Like 3 volts on the left signal, 1 on the right, but 12 on the running. That eliminates a ground problem I would think. Looks like I am going to have to take it to a repair shop as this is over my head.

You have measured voltages on each circuit.  That means you have continuity.  My thoughts:
 - You have a corroded ground connection
 - You have corrosion in the relay sockets
 - You were given the wrong relays at the auto parts store

I also recommend this product for everything electrical where corrosion is an issue:

Amazon.com: Corrosion-X 90102 Anti-Corrosion and Lubricant, 16-Ounce,...

Dan
As an Amazon Associate Lazy Daze Owners' Group earns from qualifying purchases.
2007 IB-30
Re: Towing - one tail light on toad works, one does not
Reply #12 –

 - You have a corroded ground connection
I have 12v on the running lights, it's the turn signals which are flaky, so I would think that rules out a ground problem. I get the same reading using either the white ground wire or connecting to the frame.

 - You have corrosion in the relay sockets
They look clean, but a shot of spray could not hurt
 
 - You were given the wrong relays at the auto parts store
Very possible. Ford did not have them so I had to go to three parts stores until I found them.

Wish I had some thin flat conducting wire I could insert into the relay sockets along with the relay. Early desktops used such.
Don & Dorothy
Sold our LD in June of 2023

Our boring always non-PC travel blog
Traveling Dorothy
Re: Towing - one tail light on toad works, one does not
Reply #13 –
Hi Don; you said " turn/tail lamp circuit would work for about two seconds and then the test lamp went very dim.  A circuit was there but the test lamp was very weak.  I suspected a short.  "
   Shorts cause burned wires or burned fuses, or both. A dim bulb (test lamp) is a poor connection. Somewhere there is a conductor that isn't conducting, and it is intermittent. If you can 'poke around' and have it work, it isn't fixed until you find the location of that partial open, and repair it.  Interconnections are more troubleprone than the wires, but wires can be damaged. If they are in bundles, or split loom harnesses, you would look for rock damage or 'pinch points'.
   Complicating this is the way american cars run the 2 wire system, where the brake lights are combined with the turn signals. In your 2007 these signals go through the brake pedal switch. I don't have a wiring schematic so I'm guessing here. The problem wasn't those relays under the hood. Typical scenarios for troubleshooting would be to swap those two relays to see if the problem switched from the left to the right. Cheaper and faster.
   The low voltage at the MB bumper plug on the left circuit, with the umbilical and towed disconnected, means the problem is in the motorhomes wiring. That narrows it down alot. So are you connecting at the Lazy Daze plug in the tire cover, or had LD put in a socket under the bumper that year?
   Last year I bought a 2001 for a friend, and a previous owner had added a parallel socket under the bumper by putting those nasty crimp terminals in the wires going to the factory socket. No tape or sealing and salty water had wicked in between the strands to dissolve the copper. It took awhile to splice in 4 inches of new wires. I ended up removing the OEM socket in the tire cover.
   If you take it somewhere for repair, please let us know what the 'fix' was.    RonB
RonB (Bostick) living in San Diego
Original owner of "Bluebelle" a '99 TKB
Re: Towing - one tail light on toad works, one does not
Reply #14 –
Ron,
you said " turn/tail lamp circuit would work for about two seconds
No, it starts out with low or no voltage and stays the same. More volts on the right than the left, but still low.

It's not the relays, pretty sure of that.

I am taking readings from the bare wires that did go into the 4-pin plug on the bumper. Which eliminates any problem with the connector.

means the problem is in the motorhomes wiring.
Yep, Somewhere between the bumper and wherever the wires connect in the engine compartment. I need a lift.

For $10 dollars Detroit could put an accessible connector in all vehicles to plug tow wires into.
Don & Dorothy
Sold our LD in June of 2023

Our boring always non-PC travel blog
Traveling Dorothy
Re: Towing - one tail light on toad works, one does not
Reply #15 –
Hi Don;  " For $10 dollars Detroit could put an accessible connector in all vehicles to plug tow wires into."

Don't you and I wish!  But that universal seven pin connector for RV's is starting to show up on some pick-up trucks, so some hope. But the pin-outs are still all over the place, along with the names for the signals. At least with that connector, each wire can be moved around with a screwdriver.
   So did that connector on the bumper come from LD? That is about when they moved it out of the tire cover. Take the inside cover out of your storage compartment and take a look at the wiring inside there. It's covered with that yellow fiberglass batting. Put that stuff into a bag, you'll need to put it back later. Under there is where LD used wire nuts or 'staked' crimp fittings to join up wires, among them going to the towed vehicle. I'm hoping that your tail lights still work normally on the motorhome?   RonB
RonB (Bostick) living in San Diego
Original owner of "Bluebelle" a '99 TKB
Re: Towing - one tail light on toad works, one does not
Reply #16 –
Ron, again I am taking readings from the bare wires that did go into the 4-pin plug on the bumper. The connector went in the trash. When I get 12 volts to the Yellow and Green wires I will install a new connector.

Yes, the LD lights work fine. Those are on a different feed.
Don & Dorothy
Sold our LD in June of 2023

Our boring always non-PC travel blog
Traveling Dorothy