I've been working on this method for quite some time now and I'm finally ready to post this to the blog. Finally, delicious grilled french fries!
Inside the house I cut up pretty small potato wedges. I go pretty small here, maybe in the 3-4mm range. If the fries are too thick they will not cook well. After they are cut up toss them in a decent amount of olive oil to ensure they are fully coated.
Set up the grill for a low heat. This is about 1/4-1/2 of your charcoal chimney and when you dump it out leave some space between each coal. I tried to have at least a half inch in between each ashed over coal. I could hold my hand over the grate for at least 3-4 seconds. I tossed the fries on the grate being sure to align them perpendicular to the grates to reduce the chance of a fry slipping through the grate.
I closed the lid and let the fries cook for about 4-5 min. The photo above shows the fries after being flipped. When I was working out this method I would constantly peek under the fries to make sure they weren't burning. Now I have it under control with about a 4-5 min time with a low heat. After another 4-5 minutes both sides of the fries should be nicely charred. The char plus the oil makes for a nice crispy fry.
This is where this method becomes very convenient. After the 10 or so minutes grilling the fries, I arrange them in the no heat zone stacked up and arranged neatly on the side of the grill. Make sure there's no coals on this side of the grill. This is when I'll toss some hotdogs or burgers on the low heat side of the grill. The fries can keep warm and further crisp up while you can cook your other foods. Now this won't work for steaks or other foods that need high heat, but you can get away with it with something like brats, burgers, or hotdogs which can be casually grilled over low heat. When you are ready to serve toss some salt on the fries! I think they are great!
This may seem very easy and straightforward. However, when I was looking for recipes on how to grill french fries I stumbled on methods involving par-boiling which in my opinion isn't necessary and sent me down the wrong track for a couple of months. Par boiling is only necessary if you have really thick cut fries. The key here is low heat with very thin fries and you'll be fine tossing them right on the grill.