Hi, I'm building my wiring loom and have some questions about where to use relays:

I saw the schematic in Ron's book and it doesn't show a relay for front lights.

Many other schematics (Other cars) use relays.

About the engine start button, I have one, but not knowing the amp rating, should I use one? Why normal car switches does not requiere or use a relay to drive the started solenoid?

It depends on the rating of the switches and wires you are using.

The purpose of a relay is to switch heavy currents - say 30A for a cooling fan, using a light duty switch and wiring.

I have used relays for headlights, main beam, horn and cooling fan as the Sierra column switches I have used are not designed to cope with high currents.

If unsure then I would say use a relay rather then not - they only cost ~£2 each anyway.

HTH
Nick

I may have gone a bit overboard, but I used relays on my ignition, horn, fan and dip lights. My bike loom also has a starter relay. So when I turn my key, the ignition relay sends power to the ignition side fuse block. When I press the start button, the starter relay fires.

I didn't use a relay on my headlights because I have them hard wired to the ignition side fuse block. This gives me daytime running lights.I haven't taken pictures in a few days, but you can get an idea here.

--HTH, Chris