relay fails when igntion starts

I have wired LED Daytime Running Lamps using a relay which supplies power to the LEDs whenever the car is in accessory or ignition position. However, when the car is started (key moves from accessory to ignition and back) one of the LEDs turns off. If I connect the circuit whilst the car is already running then both LEDs work. I assume the problem may be due to the large load turning the engine puts on the electrics but have no idea how to resolve it. Any ideas? Thanks!

Being Acc OR Ign (ie, diode-OR'd etc), they should stay on when the Acc disconnects during cranking. It could thus be a voltage drop problem. A lower voltage should merely dim the LEDs unless the voltage drops below their minimum voltage (eg, 1.5V or 3.0V per LED). If they are powered from the same source (+12V thru relay or whatever), then I would check their ground path. Maybe the off-LED's ground is rising during cranking or heavy loads.

If you want them to stay on, run them from IGN 1, the ignition lead that stays live during cranking (start), and relay them if there are any doubts about power loss. That fact that one side shuts down tells me one of three things. Bad power supply, bad ground, or faulty unit. Get your meter out. What car?

In fact to play safe run from the ignition NEVER ACC, do you want that drain whilst the car is just sitting there with the engine off? Then run it through a DEI 528t timer relay with a 5 second delay on.

Sorry I keep thinking about this, how much drain would you get from a group of LEDs? Bet it's less than 1 amp for both.

Thanks for all the responses! I've done some more playing around and think I can eliminate it being a grounding problem (by grounding both LED units to the same point). I can imagine that the delay timer relay would work well as connecting the circuit after the engine has turned works. Still, I'd like to try and understand what is going on just for the interest. @howie II Taking the above advice I've wired the relay to IGN rather than ACC but still the problem persists! I measured both units combined draw about 1.5 amps. Maybe I should have just used two big power transistors?. 2003 Ford Focus 1.6 by the way.

How did I guess UK? Normal name! Follow up on the ground side, the wiring should be as follows:- 87 to battery, fused at 3 amps. 30 to daytime running lights. 85 to ground. 86 to GREEN/ YELLOW, ign. switch loom. See diagram:- relay_1.bmp I still think once you've eliminated the grounding problem that one might be faulty. Try changing them around, if the original faulty unit stays faulty, I'm right, if not check your wiring/connections. This is the 528t set-up:- FZ6_528t.bmp

That last one is incorrect. I forgot the ground Revised:- Z1A_528t.bmp Yellow and red to battery via a 3 amp fuse. Orange to lights. BLACK/ white from ignition. Black to ground. Brown don't use. Cut the blue loop.

I tried changing the lights around and the problem only repeated itself with the one light unit so I've had to assume that its a problem with the lights themselves. Checking the documentation which came with the lights it recommends that the lights be wired to the sidelights and not the ignition. This is strange as it defeats the purpose of DRLs? Anyway, thanks very much howie II for the excellent work around. I've got hold of a DEI 528T and it works perfectly with your wiring diagrams. So it's problem solved, even if I'm still not quite sure why the unit only works after a delay. Thanks again!

Lights, ignition, the neighbourhood Gerbil on a wheel linked to a dynamo, who cares it worked