"I bought this Hella switch for my driving light project. Do i run a fused 12 volt wire into one side of the switch, out the other side, and to the relay?"
If that switch diagram was all they provided, it's mostly not helpful. They show a 15A fuse connection. That's probably for a direct-connection to the driving lights. Use a relay, just to decrease the length of the circuit and to reduce voltage drop resulting in reduced light output.
Connect a fused source to the switch then to terminal 86 of a standard 1M-1B Bosch relay, then to ground via terminal 85. This is the control side. Theoretically, the switch can be on any side of the relay control circuit.
"What amp fuse,15?"
Two fuses total: 5A or less on the control side, 15A should be sufficient for two 75 watt bulbs on the power side.
For the power circuit; from source voltage, create a circuit from the 15A fuse to terminal 30, then from term. 87 to a branch circuit to each driving light, then to ground. 87a isn't used.
"If so, how do i power the bulb? (bottom spade)?"
Depends on how the switch is designed. With no battery connected, check the switch continuity with an ohmmeter. You want to create a path from source to switch bulb to ground with the switch ON and an open circuit with the switch in the OFF position. In some switches, the source connection to the switch bulb is internal. Thus the bulb terminal should be connected directly to ground. Verify your findings on the bench with a battery and test leads before permanently connecting, then draw your planned circuit on paper so you have an installation map to follow.
"What gauge wire should use and should I split it off of the stereo or some other keyed power source?"
On the control side, 14-16 ga. depending on the bulb wattage and length of circuit. You can connect to any fused circuit as long as the total circuit current doesn't exceed the fuse rating. Your preference whether you want this circuit "hot" via the ignition switch or not (i.e. radio circuit source voltage is activated by the ignition switch; the headlight circuit source voltage is unswitched).
On the power side (feeding driving lights), use 12-14 ga. - thicker wire for higher wattage and longer circuit length. I suggest a dedicated fuse for this circuit at the fuse box (non-sunroof cars usually have an extra fuse position for the SR motor) or connect a separate inline fuse branched from the battery pos. post or other large gauge wire on the unfused side of the fuse box.
Maybe more info than you need. Hope this helps.
Sherwood
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