Join Date: Jan 2010
Location: Bowling Green KY
Sorry, my knowledge of electronics in general (and relay logic specifically) far surpasses my knowledge of vehicles as of this date and time.
A NC loop is a normally closed loop. Basically, when the relay is sitting in it's normal, untriggered configuration, this loop allows current to pass. A NO loop (normally open) is a loop that won't allow current to pass until triggered by a voltage applied to the trigger mechanism.
In the Diagram above, 86 and 85 are the trigger circuit (wired in such a way that when switch is thrown, it triggers the relay.
30 is known as the common (not to be confused with ground. it's called a common (c) because it's common to both the NC and NO loops). 87a is the NC loop because if the relay isn't triggered, 87a is allowing current to flow and 87 is the NO loop because it won't allow current to flow until the trigger is applied. (this actually changes depending on the application, but we'll use this definition for this example because it's the most common.)
If you were going to use that relay to do what you wanted, you'd need 2.
The first would use the switch for running lights to trigger either 86 or 85 depending on which side is positive and which is ground and whether your switch is switching positive or ground (going a little deep here).
30 would go to your battery + termanal (the lights will be grounded independantly so we'll switch the positive side.
87a be left blank and 87 would go to the other relay.
on the 2nd relay, 86 or 85 would be wired to your head lights (so when they are on, they trigger the relay) and 87 from the other relay would go to 30 with your lights being wired into 87a and 87 would be blank. That way when your head lights come on and trigger the relay, it would break the circuit.
'03 TJ Rubicon
'16 KL Latitude
'91 Cherokee Laredo, Stock - Sold
'98 XJ - burned :(