elctrical problem

On my 70 super bee all the gauges work and lights but when I was working on the carb I seen one of ther bolts that extend thru the firewall arking to thr firewall. This is one of the bolts that hold the heater box. I thighten the bolts down thought it may not be grounded and didn't see the ark anymore. I put a test light to it and bang got 12 volts. I have looked for a loose hot wire but no luck. any ideas? Thanks

first determine if the juice is coming from the heater box or if thats just where you noticed it this can be done by simply unplugging the heater box 3 prong plug and retest if you still have current where you did before if you do still have juice pull one fuse at a time and continue to test see if any of the fuses are in line with your problem

It's possible something is not grounded properly and the heater box mount has become the path to ground. Was the fan on when you noticed the sparks?