The coil is grounded to the engine. If the strap around the coil is secure, and the engine is grounded, the coil is grounded. The + will go to your battery, and the - will go to the distributor. It's a good idea to use an alligator clip, or jumper cable, from the battery to the coil. If you need to shut the engine down quickly, you can yank the wire loose easily.
