12v relay not triggering?

**shanegtr** · 16th June 2018, 08:52 PM

Just thought I'd put this out there as I've just had an issue with a 12v relay that I've never experienced before. So I've put in some DRL into my disco and I wanted to install a spare change over relay that I had lying around to turn them off when I turn on the main headlights. I used the trigger wire from the park lights that run down to the bullbar. So the voltage goes through the relay, into the LED park light and then to earth. I figured that should work fine but for some reason it doesn't trigger the relay. Its not a faulty relay as I've tried with several others and none of them will trigger the relay in this setup. Im at a loss as to why this isn't working - the only thing I can think of is the LED park lights are not allowing enough current through to activate the relay. Any ideas?

**alien** · 16th June 2018, 09:04 PM

What pins on the relay go to what?
Sounds like it’s wired in wrong to me.

**p38arover** · 16th June 2018, 09:43 PM

Compare yours to this:

**bee utey** · 16th June 2018, 10:20 PM

You need to wire the relay coil in parallel with the park light, not in series as you have done. 12 volt relays need around 8 volts across them to pull in. Current through the LED lamp wouldn't create enough voltage drop across the coil to do anything.

**sierrafery** · 17th June 2018, 06:50 PM

+1^^^, when ever you want to trigger a relay connect one side of the coil to earth and the other to the triggering source.

**p38arover** · 17th June 2018, 07:13 PM

Originally Posted by bee utey

You need to wire the relay coil in parallel with the park light, not in series as you have done. 12 volt relays need around 8 volts across them to pull in. Current through the LED lamp wouldn't create enough voltage drop across the coil to do anything.

They were my first thoughts when I read the OP but then I changed my mind. I didn't think anyone would wire it that way and it was just the way the post was written.

**shanegtr** · 18th June 2018, 02:04 PM

Ok, just for some clarification. Power for the DRL goes into pin 30 - then out to 87a (being a CO relay it swaps to pin 87 when the relay locks in)
The park light power comes into pin 85 then out pin 86, then to the LED park light and from there to earth.

I've wired some DRL into a previous vehicle in exactly the same why, however the only difference was that it had an incandescent park light rather than an LED as is the case here

Tombie · 18th June 2018, 02:56 PM

Correct... so you need to bypass the LED Parker and go direct to earth for the relay to switch.

The Parker needs it’s own feed from before the relay, through it and then to its own earth.

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