It's not as bad as it looks.
To do what I did... you run a data cable to the switches. In this case, it's #20 AWG stranded wire. (Never use solid core in a vehicle, it will fatigue and break)
Power and ground to the switches is run through the same cable. Ground is needed for the switch's indicator lights. Loop the power and ground to all the switches. The other colored wires go from the switch's on side (Goes live when the switch is on) to your relay coils, in the case of the usual Bosch relay, that would be terminal #86.
If you use a fuse block like I did, then your individual fused power feeds will go to each relay's terminal #30. You can also tie all the power wires together at the end of a large wire, and ''fan out'' smaller ones (Like #12AWG) for all the relays. We've done that in many cop car builds.
Ground all the relay terminals #85. (#85 and #86 is the relay coil, and a lot have internal polarity diodes, so you need to make sure power is to #86)
The only thing left is each relay's #87 terminal, which powers your lights and whatever.
The main advantage of relays is your accessory switches only power on relay coils at about 0.1 amp each. Your switches will last forever. The relay can carry the heavy loads, and you only need one big wire to power everything.
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Originally Posted by cico7
