Relays!!!

 Through theory, I only know that "A relay uses a low amperage circuit to switch on a higher amperage circuit"(theory note). Now I understand what its for.
By the wiring diagram, from the battery, we have to spit into 2 parallel ways through the relay compound. It is divided into 2 parts: control circuit, at which we wire the battery with the 86, and out put is 85, then wire it to the switch creating a negative switch. The other one is the switch circuit, which consists of 1 input the 30 and 2 outputs 87 and 87a. Now this is where i realize that it is just the logic that my head keeps spinning.
The resistance from 86 to 85 is 75.1, from 30 to 87a is Infinity, so is from 30 to 87.  This is because without the negative switch closed, the relay can not pull the switch from 87a back to 87, so as the relay stays off, the switching circuit between 30 and 87a is NORMALLY closed. And there is a switching circuit that is NORMALLY open when the relay is off, it is 30 and 87. When i try to wire a similar diagram to the relay, i try to measure the Amperage through 86 and 85 while the relay is on, the result is 0.16A, a small amount. So any doubt about the theory is finally rectified that the switching circuit uses a small current to switch on the big current for the main consumer circuit.
To demonstrate our full understanding of the relay, we are to bulb a circuit showing a relay circuit controlling 3 light bulbs in parallel:

When

When the Neg switch is closed, 85 n 86 are completed, and a current of 0.16A is through them, which excites the mag-coil, creating mag-force to pull the switch from 87a to 87. That's the whole job of the relay. Now, with the 30-87 closed, the three bulbs will light, and a large current measured is 0.75A.
Because the 87a is normally closed when the relay is off, hence it can be used to switch between "high beam" and "low beam" similarly to real car application. So, hereby the AV @ 87a when the relay off is nearly equal to the supply voltage e.g 13.4V and 13.11V, while AV @ 87 is Zero, and vice versa.
A big Voltage Drop can also be found across 86 and 86 when the high resistance relay coil (approx~75Ohms) consume almost 13V of the supply AV. Evidence is the AV @ 85 is 13.39 when Off and 0.38 when ON.

By this wiring, we can switch between low beams and high beam by OFF and ON. On a further context, some headlamps are designed that low beams remain turned on when the high beam mode is turned on.

In the event off 87a is already on when the relay is off, a bridge is made so that supply goes straight to the low beam circuit, small bridge, just enough to provide sufficient current for the 2 small bulbs. When the 30 and 87a is connected, the bridge will be shorted. When the relay is on, High beams are on also small beams remain On.