ground wire sparking? opinions?

I have a 1977 Jersey Dawn 40' with twin chrysler 440's. There are 3 different wires that come down from the electric panel and ground to the engine block. I was taking them off for and engine rebuild and one of them sparked. The other 2 do nothing if touched to the block. I have no 12 volt items turned on.....that I know of.

Preliminary tracing shows the wire is somehow connected to the cabin 12v. lighting side. With the cabin 12 volt lighting off, a 12volt bulb tester shows a weak light when I connect the wire to the engine block. If it is not connected the cabin 12 volt system will not work.

Does a 12 volt ground wire ever spark without the lighting off? Should it spark with the lights on?

Strange......

Have had unexplained battery draw down......maybe this is the source of the problem?

i would look at all the cabin bulbs and make sure some one did not install a dual filament bulb instaed of a single filament one. its a good place to start....

Well, you found why your battery was drawing down. Basically, something on that circuit is drawing power, which causes the sparks when you disconnect the ground wire. Hook up a voltmeter between the block and the ground wire then go through the process to disconnecting each item powered by that circuit, one at a time, in order to isolate the faulty device. When the voltmeter goes to zero, you found it. As crankbait suggested, try the light bulbs first. It has been my experience the problem is most often caused by a corroded switch.

I found that a 12 volt light was on. If I turn off that light the ground wire does not spark. The whole 12 volt lighting system grounds to this wire connected to the engine block.

I was told that this is normal and not to worry about it.