Update: problem not solved........ yet.......

New relay installed - this one is a Beru brand WITH a strip fuse; my mechanic said this is what they make now because it is easier and cheaper to replace the little fuse than it is to replace an entire relay when it fries. Does this sound right or is this taking a step backwards with this setup?

Here's where it gets interesting. When the new relay was installed, he turned the switch and it immediately blew the fuse. So, that means it wasn't the relay to begin with. (Don't worry - my mechanic already said he will pay for the new relay since that wasn't the problem.) Now the task is to find out where the short is - either between the ignition and relay, or between the relay and the plugs. If I were a betting man (which I am not, ironically living in Las Vegas) my bet would be that it has a shorted plug, but I'm not sure. Would just one shorted plug cause this scenario or would it need to be multiples?

The other question relates to the electrical setup in my GreaseCar system. I don't have the original manual/map/photos that came with it (for some reason the mechanic who installed it didn't give it back to me and I haven't called to ask for it back yet) but the switch/fuel gauge is wired with power ALL the time. My current mechanic wants to find out where they hooked up the power to this system and if they piggy-backed it onto the GP line somewhere, and then if that would be enough to cause this problem. I'm still hoping it is something simple that we can easily fix. Obviously, I think the easiest fix would be something downstream from the relay to do with a bad plug(s) and hopefully it is not something upstream between the relay and ignition.

Any other input is welcomed! Thank you all for your help and encouragement!