I do auto body restoration for a friends body shop. Can you look at the back side of the panel? Many times, pin holes are a sign that that whole area is compromised and rusted pretty thin...I've not had very good luck trying to weld rust hoels shut as they will either blow a larger hole due to the panels being thinner from rust, or the weld is real nasty as the rust on the backside pulls into the puddle creating a real mess.

Your best bet is to cut the area out and weld in a patch section...will be a longer lasting repair IMO.

BTw, the technique I find that works best on thin materials is to pulse the arc on and off with your finger. This keeps the heat low and distortion down, but keep a wet rag handy to cool the welds as you go. When welding patch panels I recommend welding about 1/2" to 1" long beads at a time, cool with wet rag and move to another area...skip around to minimize distortion.

Those above me are giving good advice.

I have found that this works for rusted repairs (Thicker metal and wire but I think it will scale).

Start above the hole hopefully on a spot with better metal but close to the hole.

Shake your hand back and forth like spraying paint but way faster as you move down to below the hole. Don't expect to see anything resembling welding through the shield.

After a couple of passes you should get some buildup on the edges of the hole (along with a bunch of spattery stuff around the hole that you can grind off later).

Now you can either continue this untill the hole fills in or change to the trigger pulsing method described above.

If things are too rusted out the result may be "cut out bad part" from Goose's post.

Try on scrap first.

Hope it works for you

Bill