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**Country Campers** · 06-13-2022, 11:01 AM

I wonder if there is a loose connection in the trailer box where the cord is attached to all of the other wires in the trailer. Follow the trailer wire down to the tongue and you should find a sliver box with all of these connections, remove lid and check for anything amiss.

Brian

**Johnww** · 06-13-2022, 12:21 PM

I had a simular problem with my 303 RLS. Left side tail light and brake not working intermittently and getting warning message from my Ford. Turned out to be a bad ground wire on the light fixture. I installed a new ground wire and the problem was solved. The light bulb fixture is kind of flimsy.

**bnjhikers** · 06-15-2022, 08:13 PM

Originally posted by Johnww View Post

I had a simular problem with my 303 RLS. Left side tail light and brake not working intermittently and getting warning message from my Ford. Turned out to be a bad ground wire on the light fixture. I installed a new ground wire and the problem was solved. The light bulb fixture is kind of flimsy.

Can you explain how you did that?

**bnjhikers** · 06-15-2022, 08:19 PM

Update: We took the truck to our long trusted mechanic. He tested the truck 7pin with a trailer adapter. All the signals were fine. Mechanic swears it’s a trailer problem. But why does it work with our friends truck but not with ours?

bought a bottle of deoxit and tried that today. One pin had a tiny spot of green. No change in the left blinker.

called Grand designs, they suggested checking the light module wiring.

we will look at grounding wires and light modules next.

**StephenO** · 06-15-2022, 08:43 PM

When we were getting random 'Trailer Disconnected' messages on our F150, I opened the junction box near the tongue and removed the Marrette on the grounds, I found one of the wires had some loose strands. After cutting that wire and stripping to fresh copper, I put everything back under the Marrette and the issue hasn't happened since. A replacement junction box with ring terminal connections is on the long-term to-do list...

My take on your question about the issue not happening on your friend's F250, is likely your trailer wasn't connected long enough for the error to come up.

**TucsonJim** · 06-15-2022, 08:49 PM

Originally posted by bnjhikers View Post

Update: We took the truck to our long trusted mechanic. He tested the truck 7pin with a trailer adapter. All the signals were fine. Mechanic swears it’s a trailer problem. But why does it work with our friends truck but not with ours?

bought a bottle of deoxit and tried that today. One pin had a tiny spot of green. No change in the left blinker.

called Grand designs, they suggested checking the light module wiring.

we will look at grounding wires and light modules next.

Wow - This is really getting interesting. If it works fine with the other truck, I'm thinking it has to be a problem with the truck. Just a thought. If there is an interface problem with the 7-way on your truck and trailer, it may be okay with the other truck. For example, if the pins on your truck's 7-way are slightly thinner, and the sockets on the trailer 7-way are a little loose, there could be a connectivity issue.

Do you know anyone who has another trailer you could plug into your truck?

Jim

**Jlawles2** · 06-16-2022, 06:42 AM

That sounds like a broken wire or a bad connection. I would start by trying to find the connection between the tail light and the wiring from the front. May need to drop the coroplast and / or pull the light. I would start with the coroplast.

If you do not find the issue there, start following the wire toward the front feeling every inch for any types of damage. Inspect any of those dreaded trailer connectors as they are known to destroy wiring.

**Johnww** · 06-17-2022, 11:00 AM

Originally posted by bnjhikers View Post

Can you explain how you did that?

I removed the tail light lens then removed the screws in the light fixture itself. In then pulled the fixture out as far as it would go and then noticed the ground wire yont he fixture was partially detached. I then ran a new wire to the frame and attached it to the light fixture.

**bnjhikers** · 06-30-2022, 10:27 PM

Update. It rained here. I went out and checked the left tail light and sure enough there was water in it. Pulled the light, drilled a tiny drain hole. Connections were good. Left turn signal and brake light still not working. I ordered a new light. Took the truck to the ford dealer, they could not find anything wrong with it. We're taking the trailer to have the brakes and bearings serviced. They will check wiring for the left tail light, if the new light doesn't fix the problem.

Thanks for all your suggestions. I think it could be:

@TusconJim idea that the 7 pin plug could be loose.
@StephenO I need to check the junction box connections
@Jlawles2 bad connection/ wiring issue

**bnjhikers** · 08-06-2022, 11:49 AM

NEW UPDATE.

I will spare the details of the iterations we've gone thru and jump to what I think is the final solution.
We replaced the junction box with a Mictuning Heavy duty 7 gang Junction box and 8 ft trailer cord.
After doing this the left turn/brake signal still did not work.
But we were stumped by why did the left turn/brake signal had 2 RED TRAILER wires while the right turn/brake signal only has 1 brown trailer wire.

We tested the red wires independently and with one of them the left turn/brake signal works perfectly. Still need to test it driving on a downhill grade as that is how we found we could trigger the light module fault.

Why did Grand Designs run 2 RED TRAILER wires to the junction? A mobile tech we worked with that some units require the additional wire and we can just leave it off.

Agree/Disagree?

Thanks for all those who helped with this issue! We learned alot!

**howson** · 08-06-2022, 01:16 PM

Originally posted by bnjhikers View Post

NEW UPDATE.

I will spare the details of the iterations we've gone thru and jump to what I think is the final solution.
We replaced the junction box with a Mictuning Heavy duty 7 gang Junction box and 8 ft trailer cord.
After doing this the left turn/brake signal still did not work.
But we were stumped by why did the left turn/brake signal had 2 RED TRAILER wires while the right turn/brake signal only has 1 brown trailer wire.

We tested the red wires independently and with one of them the left turn/brake signal works perfectly. Still need to test it driving on a downhill grade as that is how we found we could trigger the light module fault.

Why did Grand Designs run 2 RED TRAILER wires to the junction? A mobile tech we worked with that some units require the additional wire and we can just leave it off.

Agree/Disagree?

Thanks for all those who helped with this issue! We learned alot!

Did you have all the other wires identified and they are connected to the Mictuning and there's still and "extra" red wire? At some point it's my guess you'll find something doesn't work...(rear camera power? TPMS module?)

**bnjhikers** · 08-06-2022, 05:14 PM

Everything is reconnected except that one extra red wire. The left turn works fine without it. With the extra wire we started getting a trailer light module fault this year. Last year no problems.

It may be for the Back up Camera. We have a Furion Vision S. I need to test it.

Pics are from before we changed to the Mictung box. last pic was all the trailer wires coming into the box. The blue brakes connection has an extra black wire for the breakaway trailer switch.

**bnjhikers** · 08-06-2022, 05:19 PM

addendum: the furion installation says you can connect to running lights, reverse lights. This is something preinstalled by Grand Designs. I'll call them tomorrow.

**TucsonJim** · 08-06-2022, 05:54 PM

Here is a photo of my wiring if it helps.

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Ford Random "trailer light module failure"

Ford Random "trailer light module failure"

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