Troubleshooting stray voltage tips...please

[UncleWillie]

...This is a potentially dangerous condition here!

+1

...At least I semi understand how jacked up my electrical accessories are...Winter project I suppose ...

This is NOT a Winter Project Item!
This project goes to the Top of the List, Now!

Until you know why you were shocked while standing barefoot in the garage and touched an object that should have No electrical connection at best, and was Grounded at worst; you should avoid touching anything in the Garage.
The Garage is now OFF LIMITS to the rest of the family.

Replay the scene, and place the Wife/Kids/Grandkids/Neighbor in your place.... Do you need the full picture?

There should be no reason you should not be able to safely stand barefoot in a puddle of saltwater and have Zero risk of being electrocuted. Find the problem and eliminate it before someone gets seriously hurt.

This is the part where I step down off of my Soapbox.

If you need help in locating the source of the problem let us know. We will all be glad to assist. Be careful.

 

[UncleWillie]

Lets eliminate the house wiring first.

Using the same extension cord that caused the shock; Plug it into the same outlet that caused the shock.
Using your Voltmeter and a puddle of water on the garage floor. Measure between the sockets of the extension cord and the puddle of water.

Round Ground Pin Socket to the Puddle should measure Zero Volts.
The Common, Larger Slot Socket to the Puddle should measure Zero Volts.
The Hot, Smaller Slot Socket to the Puddle should measure ~120 Volts.
The Hot, Smaller Slot Socket to the Round Ground Pin Socket should measure the same ~120 Volts or more, but Not less.

If these all measure correctly, the house wiring is likely not the culprit and the family can enter the garage again and you can move this project down your To-Do list a level or two. Using the charger is still not recommended until the leakage current is isolated.

If any of the measurements are incorrect, The house wiring has a problem.

 

[UncleWillie]

The charger or the house power is the culprit.................It is not a 12 volt issue, one or the other needs to be ruled out. then by default it is the other.
That's called trouble shooting 101 process of elimination.....
Non of us are there......... I do not know the site conditions, for all I know the garage/shop is fed from the house by an extension cord buried by 2 inches of sand...........who knows......

I like your though process. It is colorful and makes me think.
I have no issues at all with troubleshooting, it is my forte.

The Extension Cord Buried in Sand running from the hose to the garage, while graphic on the surface, is no different that any other power conduit to the garage. A branch circuit Fault is still a Fault regardless of the Implementation.
There is no reason that a buried extension cord is inherently unsafe.

True, at this point we do not know how the AC power is delivered to the garage.
I would be interested in hearing a fault theory that fits the described symptoms.

Bruce's theory of a metal chassis'd charger, contacting the hull, with a leaking internal circuit and a floating ground either at the charger or in the Mains supply, is a feasible theory. It involve a Faulty Charger but not necessarily a Faulty power circuit.

My bets are On, or is it Against???, the Charger.