I've read that thread before. Most of what it says is true, and in fact that's what I just told you to do.
The difference is, first, there is actually more than one ground wire in the engine bay from the factory. I know there are at least two, and I'm pretty sure there are four. The shop manual has detailed instructions for inspecting them.
Second, you don't need to add a ground cable in the frunk if the one that's already there is clean and in good condition. Detach it from the battery and use a little piece of sandpaper inside the terminal, and on the battery's terminal. Put it back on. Done.
You could accomplish the same thing Tom's thread tells you to do for $0 by just removing all the stock ground cables, sanding the terminals lightly, and then reinstalling them. No need for new wires at all, unless one of the original ones is missing.
Edit: I just remembered: the ground cable on the right connects to the engine side cover mounting point. IIRC, it's a black wire with yellow stripe.
That makes at least three:
1. On top of the transaxle. Connects to the aft firewall, as I recall.
2. Under the intake manifold. Also connects to the after firewall, I think.
3. Right side of the engine. I think the lower end is down near the alternator somewhere. The upper end goes on one of the tabs for the right-side engine side cover.