They are not designed for continuous duty like that. I do use one for the starter circuit though. I put it down on the frame by the starter & wire it it to the solenoid. There are HD relays available for continuous duty, high amps. but I wouldn't run my HEI through it. You can get the small relays that are common on today's vehicles & run one each for heater & headlights. I would use a much larger fuse block. With all the accessories we add on today its good to have each one on a separate fuse.
