I build Mark VIII fan kits for gbodies and I can tell you a cheapo 30-amp relay ain't gonna last long. If you are going to use a relay, go with al least a 60-amp one. I use Hella HD 70 amp relays for mine. And make sure it has a tamping diode internally...this way, you are assured current only flows in one direction-to the fan just in case the relay contatcs ever stick closed. The fans I use-RF64 which is 90 amps at start up for a few milliseconds and 32 amps at full speed will smoke as 30 amp relay and even a 40 amp relay will get pretty darn warm. Use high quality 10 gauge wire for power for relay and fan lead. Your 78 amp alternator will handle it but remember, when amperage goes up, voltage comes down. And when amperage goes up, heat is built up in the wiring. You will notice other things like headlights dimming, heater blowing slightly more slowly, etc. when runnign the fan at full speed. There are a lot of ways to modify the factory vehicle charging system to take better advantage of a higher output alternator but that's for another thread...lol. If you are running stock v-belts, I have a solution for you that will give you a high output alternator for a lot less money than you think and involves only a little re-wiring. Go to a parts store and pick up an alternator for a 1988 Oldsmobile Firenza 4 cyl. It is rated at 90 amps and the serpentien pulley can be swapped out for your v-belt one. And guess what else? It has 12 and 6 clocking so it will directly replace your old alternator (assuming we are dealing with a 305 or 350 engine here). Now, go to the HELP section and grab the CS style alternator pigtail...it'll have three wires-black, white and red. The black one is not used (diesel tach lead), the white splices into your factory brown alt. wire (dash gauge lead) and the big red wire splices into your red lead on your factory alt. wirng. The main charge post wiring goes to battery +12V. Done-90 amps and super easy to do! That's just one of the many little tricks I have for modifying the charging system. The alternator is about $60-70 bucks and the alt. pigtail is about $10.