Anyone know if the Sierra light switches can carry the load of the dip / H beam lamps or do you nead a relay. i notice in the Haynnes manual that most models use a relay to feed lights.

if you want a hand heater (read fire at the switch) wire the lights direct if not use a relay. ford really did skimp on the wire size on the sierra and was marginal to say the least on the feed to the lights from the relay (don't put 100w bulbs in the standard sierra loom)

Thought as much. It was just that the Luego loom I have states "you may need to use a relay"
I will fit relays to both headlight functions.

cheers