what circuit are you putting the relay in? what circuits did the fuse box handle? fuses and relays are different animals, either might not be the most appropriate safeguard for any given component and how a relay is connected depends on what you want it to do

for the truck to run all you need is a wire from the battery to the starter and one to the coil + , neither of which is fused

Bill

Moved over to the Passing Lane

"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir
"When we tug a single thing on an old truck, we find it falls off" ~ me
Some TF series details & TF heater pics