Here's the general concept with a relay:

You've basically got four connections, and they've got all sorts of names. I'm using the ones I think are most descriptive for your purposes.

You've got a supply, an output, a trigger, and trigger ground.

The relay is a switch, just like a light switch, but instead of using your finger it uses 12 volts DC to flip the switch.

When 12 volts is present, the switch is on- no 12 volts, switch is off.

The supply and output are the two "switch" connections. When 12 volts is present at the "trigger" connection (the electrical "finger") the switch is on. It really doesn't matter what the "supply" and "output" are connected to: you can hook up the fusebox headlight power supply on one and the headlights on the other and as long as you've got the trigger set up right the headlights will come on.

The trigger is the wire from the signal stalk. This provides 12 volts DC when you pull the stalk. The trigger ground is provided by screwing the relay tightly to the steel of the car.

So- how to test?

Attach the relay tightly to the body of the car in such a way that you can connect wires and a tester as needed. Have a continuity tester handy. Connect the "trigger" wire (from stalk) to the appropriate connector on the relay (grey). Check for continuity across the two other connections- "supply" and "output". They should read "open" or "zero" on the tester (or no beep if the tester beeps).

Now turn on the ignition, turn on the headlights, and pull the stalk for high beams. Check continuity across "supply" and "output". It should now be "closed" or "1.0" (or now you'll get a beep). This means the trigger has made the "finger" flip the "switch".

If you are feeling daring you can just hook the relay up as follows-

Grey- stalk wire
Black- fusebox supply voltage
Double Red- headlights

Bear in mind it's your choice to bet I'm right without testing it first....

-Dylan