Hello I have an older home with a detached garage, with electric but no ground wire. I want to add a small to circuit panel how can I put a ground bar outside my garage and run that to the circuit panel then run my new wires from that?

Before you install anything you need to make sure you properly size the amperage needed for the garage and that the correct panelboard is selected for use in the garage.

There are specific requirements for power in a remote building.

Number one on the list is a four wire feed (unless you only have one circuit or one multi-wire circuit.

That 4 wire feed cable is dependent on how much amperage you are going to deliver to the new panelboard.

Also, you must put a light on the external entrance (not a garage door).

At the new panelboard, you cannot have ground and neutral bonded together, they must be isolated.

Also, you must install at least 1 grounding rod and one electrical grounding conductor from the ground bus to the garage electrical panelboard.

One reason you are not allowed to bond neutral and ground at the garage panelboard is the "ONLY" place where ground and neutral can connect is at the main service panelboard.

The ground rod and grounding system at the garage is required to protect the building from electrical surges like lightning.

All receptacles in the garage should be GFCI protected.