ALWAYS un-hook the ground cable to the battery first and reconnect it last.

If you touch metal with the wrench while touching the ground post nothing bad happens.

If you touch metal with the wrench while touching the hot post nothing bad happens IF the ground cable is already removed.

If you touch metal with the wrench while touching the hot post and the ground cable is not removed bad things can happen.

'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.