D2 Taillight/Indicator Trailer Harness Conversion

[dbeard]

Hi Gang,

So I attempted to use the 3 to 2 wire trailer wiring harness to get rid of my indicator lights in preparation for a greg davis bumper. I successfully achieved my brake lights acting as my indicator lights as well, but I'm having an issue once I apply my foot to the brake, then the lights begin to blink faster, as if it is indicating that a bulb has failed.

Has anyone had similar issues with this conversion? Is there any way to have the indicators and brake lights behave normally??

Thanks

 

[listerdiesel]

If you have the standard electrical socket behind the passenger side light cluster, you'll have separate feeds for everything, 6 connections plus earth:

The system runs separate relays for LH and RH indicators and the IDM module in the passenger fuseboard senses bulbs being connected so the slave trailer indicator in the dashboard lights up when you have a trailer connected.

If you change that, you will get some odd results, especially if you back feed the IDM through the brake light circuits.

Peter

 

[KyleT]

Ya it won't work. I even tried dummy load resisters and same issue. Fast blink Ect... So I cut holes in my bumper and put oval trailer lights in.

Edit, not a gd bumper though.

 

[listerdiesel]

There are ways of doing it electronically, but a lot of faffing about for such a small return.

Peter

 

[listerdiesel]

Just for the hell of it, I've had a look at how it could be done.

You will need 2 relays, 12V auto type, single pole double throw, plus 2 diodes, something like a 1N5401 or P600A.

The relays take their feed from the two indicator feeds on the trailer socket in the car, the other side of their coils go to ground. So if the indicator on either side is running, the relay will go on and off with the car indicators.

The wire to the trailer stop lights has to go to the common contact of each relay only. The normally closed contact of the relays goes to each stoplight on the trailer. Thus in the event of a relay failure the stop light circuit still works.

So when the flashers aren't running, the stop lights work normally, but if the indicators are running, the stoplight feed to the light on whichever side it is will be interrupted by the relay contacts.

That's fine if your brakes are on at the time, but no good otherwise, so you wire each of the diodes into circuit so that their negative end goes to the relay feed from the car indicators, and the positive end with the silver band goes to the stoplights BEFORE the relay contacts. Thus the diode will provide the 12V flashing feed to the stoplights if the stoplights aren't running, and the lights will flash. There is a small voltage drop in the diode of 0.6V approximately, but that shouldn't affect the lights in any significant way.

I'll sort out a schematic later and post it here. The tail light circuit remains untouched. This arrangement leaves the IDM with no back feed to screw it up, but I haven't looked at getting the trailer indicator on the dash working yet. If the stoplights are not in use, the extra current from the stoplight bulb will trigger the IDM to light the trailer slave light on the dash, but when the stoplights are on, the additional current won't flow as the stoplight circuit is feeding the bulbs.

Peter

EDIT: Changed the diode output point.

 

[listerdiesel]

Just found a snag, working on it...

Peter

 

[listerdiesel]

OK, have a look at this schematic:

Looks to fulfill the requirements, but has to add a couple more diodes as the stop circuit feeds both sides together.
Peter

 

[dbeard]

Wow Peter, thank you so much for the abundant info. I think I'll just deal with the fast blinking for the time being until I get motivated to put in a work light, and rewire my reverse lights for indicators.

 

[Gman]

OK, have a look at this schematic:

Looks to fulfill the requirements, but has to add a couple more diodes as the stop circuit feeds both sides together.
Peter

This is fantastic. Thanks! The fast blinking drives me nuts.

 

[helievacpilot]

How about one of these? http://www.google.com/imgres?sa=X&b...&ndsp=31&ved=1t:429,r:3,s:0,i:90&tx=115&ty=77

 

[JohnB]

Could this just be achieved by using euro-us trailer adapter, them use the leads from that to your turn/brake light bulb?

 

[mbrummal]

You could also just turn off the fast blinking in the BCU.

Wow Peter, thank you so much for the abundant info. I think I'll just deal with the fast blinking for the time being until I get motivated to put in a work light, and rewire my reverse lights for indicators.

Also, that is what I did.

 

[dbeard]

How does one turn off the fast blinking in the bcu?

 

[KyleT]

How does one turn off the fast blinking in the bcu?

Never seen that option. It's because the load is less in the resister timer circuit therefore it blinks faster.

 

[dbeard]

You could also just turn off the fast blinking in the BCU.





Also, that is what I did.

Any info on how you turn this off?

 

[listerdiesel]

The indicators Bulb Failure Warning in the BCU can be turned off.

May not be legal in some countries to turn it off.

It is listed in the BCU functions in RAVE, page 1481.

Peter

 

[helievacpilot]

OK, have a look at this schematic:

Looks to fulfill the requirements, but has to add a couple more diodes as the stop circuit feeds both sides together.
Peter

Bringing this one back from the recently dead. I'm going to put this circuit together and understand the diode hook-ups but not the relays. I'm enclosing a pic of a typical 12v spst relay. Could someone enlighten me as to the connections to each of the 4 relays? I see only 2 hookups to each relay in the diagram, but there are 4 possible connections on each relay itself.
Thanks - Bill