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Good afternoon, I have recently ordered a normally closed relay to fix on my car's daylight-running lights. When the main lights come on the DLR should switch-off. Unfortunately amazon has delivered instead of a normally closed 2 normally open relays (!!?). Is there a clever way to emulate the normally closed relays functionality with two normally open relays? Thanks in advance.

regards perry

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  • $\begingroup$ Wouldn't it be easier to just return the items sent in error and get Amazon to send the correct part? $\endgroup$
    – Eric S
    Feb 1 '20 at 23:42
  • $\begingroup$ @Eric: Where's the fun in that? $\endgroup$
    – Transistor
    Feb 2 '20 at 10:50
  • $\begingroup$ yes, it would be easier. unfortunately i am stuck with the parts in a remote place for now. so making the best out of it, and actually is fun to find a way to get it going still. :-) $\endgroup$
    – Perry Hall
    Feb 3 '20 at 18:24
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You have a chance. This might work as a temporary solution.

enter image description here

Figure 1. Switching DLRs off with an NO when headlights are on.

How it works:

  • When the ignition is on and the headlights are off the headlamps will provide a low enough resistance to allow the RLY to pick up. The normally open (NC) contact will close and the DLRs will turn on.
  • When the headlamps are on there will be 12 V on both sides of the relay so no current will flow and the relay will drop out switching off the DLRs.

enter image description here

*Figure 2. Modification to detect both dip and high beam status.

  • The DLRs will turn on only if both DIP and HIGH are off.

Note that in both circuits I've powered the relay from a line switched by the ignition. This will avoid draining the battery when the ignition is turned off.

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  • $\begingroup$ this sounds like a good proposal. i will try to find an ignition plus in the fuse box in the engine compartment and take it from there. $\endgroup$
    – Perry Hall
    Feb 3 '20 at 18:20
  • $\begingroup$ thanks for taking the effort. i tried to upvote your post, but i have not enough reputation, as i asked what seemed like not so good questions in another threat. $\endgroup$
    – Perry Hall
    Feb 3 '20 at 18:26
  • $\begingroup$ Let us know how you get on. $\endgroup$
    – Transistor
    Feb 3 '20 at 18:30

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