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Technical The trailer brake lights work, but turn left or right lights not

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Technical The trailer brake lights work, but turn left or right lights not

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feifeilake2

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Hi, I just had my Stilo 2007 1.6 16V installed a tow bar in a garage. Then the beep sounds much quickly (turn left or right with trailer connected) than without a trailer. The break lights work but not turn lights in the trailer (a new trailer, the trailer works well with other cars), and also the turn lights on my car are also disabled when the trailer is connected (return to work after disconnect the trailer). I went back to the garage, and the strange thing is that the tow bar worked well with two different electronic testers/indicators. What is the possible reason? Thank you in advance!
 
Thank you dtimmins1985 and irc! I'll check the lights on trailer. One stupid question: what kind of lights should be used instead of LED, or how to change the LEDs? Thanks!
 
If your trailer does not have LEDs, make sure your towbar electrics were installed using a bypass relay. Directly connecting to the wiring in the boot can also cause these types of problem as the body computer (BCU) sees unexpected loads on the tail lights.

If trailer uses LEDs then...
Many standard trailer electrical kits still only support normal (incandescent) bulbs. This normally only visibly affects indicators as they have to be monitored for bulb failure. (Some higher-end kits also monitor the other bulbs, but they usually support LEDs anyway.) LEDs have a different resistance and look like a blown bulb to the BCU.


The usual ways of sorting this are by:
a) Changing indicator LEDs for old-school incandescent bulbs, or

b) Adding "CAN-BUS" type resistors to the existing LEDs, or

c) Upgrading the towbar electrics to suit LEDs.

As I understand it, the "correct" way would be option c, as either of the other two could invalidate the "certificate of conformity" for the trailer, but until the UK MOT test catches up you may find that the towbar electrics may fail the MOT. Not sure about tests in other countries.

It seems that most people go for option a.
 
Hi irc, Thank you for promptly and detailed reply! I'll contact the trailer company first to know if they use LEDs or not?
 
The trailer producer just told me that there is no LEDs in the trailer, only bulbs.
 
irc said:
If your trailer does not have LEDs, make sure your towbar electrics were installed using a bypass relay. Directly connecting to the wiring in the boot can also cause these types of problem as the body computer (BCU) sees unexpected loads on the tail lights.

If trailer uses LEDs then...
Many standard trailer electrical kits still only support normal (incandescent) bulbs. This normally only visibly affects indicators as they have to be monitored for bulb failure. (Some higher-end kits also monitor the other bulbs, but they usually support LEDs anyway.) LEDs have a different resistance and look like a blown bulb to the BCU.


The usual ways of sorting this are by:
a) Changing indicator LEDs for old-school incandescent bulbs, or

b) Adding "CAN-BUS" type resistors to the existing LEDs, or

c) Upgrading the towbar electrics to suit LEDs.

As I understand it, the "correct" way would be option c, as either of the other two could invalidate the "certificate of conformity" for the trailer, but until the UK MOT test catches up you may find that the towbar electrics may fail the MOT. Not sure about tests in other countries.

It seems that most people go for option a.
Click to expand...
Did the garage fit a bypass relay? As asked in the excellent quoted post.
If you don't know you need to ask garage that fitted tow bar and wiring.
 
HI all. As a long shot,did the garage do a proper job and solder the connections, or did they use those blue clip connectors( easy option).It's just possible that a good connection has not been made at the lights connection.
IRC is probably on the right track.
 
Thanks to all of you! I have reserved a time (tomorrow) with the garage to let they check what's wrong they made. I'll let you know the result.
 
Thanks! I went to the garage with the trailer. First they told me there was a wrong wire connection after tested with a new electric tester. Changing the wire and then we went out to connect the trailer. Problems were still as before. They told me they had to talk with another garage to find the reason. They may contact me next week. This is the first time that they didn't know what to do (of course they only did mechanical jobs for my car). At least they are not good at electric connection tasks. By the way, I also asked if they installed the bypass relay there, the answer is they are not sure. So they only took a so-called electric kit to use it.
 
Last edited:
Ewwww doesnt good, get a decent competent person to re-wire it with a bypass relay... shouldnt cost that much, i could do it for you and have it done in less than an hour... talking £35 tops if u find the right person
 
After more than two months, the problem was solved yesterday at last. The problem was caused by the simple wiring (directly connection without a bypass relay). They said that simple wiring is the traditional way (is it true?). After many tests, at last they decided to follow my suggestion to install the bypass relay to my car yesterday. Now the lights work well (by the way, "break" in the title should be brake, thanks for understanding!).
 
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