The US Prius passenger inner vent panel is on the left, the J Prius driver's inner vent panel is in the middle, a J Prius panel with some trimming done is on the right.

US panel left side view.

J panel left side view.

US panel left side view, you can see it is smooth, no tabs.

J panel left side view, you can see that it has tabs that will need to be trimmed off.

The back side of the panels, J panel on top. You can see that the J panel has a hole for the Park button where the US panel has 2 tabs to help hold it down. Not having these tabs on the J panel isn't an issue, it holds fine without them.

Trim off this tab first, so you can snap the vent panel into the dash.

With the J vent panel on the dash, you can see where the tabs/protrusions interfere with the gloveboxes...

...especially the glovebox buttons.

With the J panel on the dash, you can see that some of the dash needs to be trimmed out of the way to fit the tach. None of this is structural, so trim away.

I marked the dash with the J panel in place, here you can see the trim lines. The trimming needed depends on the size of your tach. I actually ended up trimming well above the lines, up next to the 2 rectangular holes above them, as I placed screw mounts over those 2 holes for the tach mounting plate I made from ABS sheet.

Here you can see that the wire bundle behind the tach area is set far enough back to not be an issue if you use a shallow tach like I did (Nordskog digital tach from Summit Racing).

Once the dash is trimmed out of the way, the wire bundle behind the tach area has an illumination wire you can use for the tach illumination (circled, light green wire). You can also see the screw hole below the opening, that is one of the stereo/pocket mounting screws that I used for my tach mounting plate.

Trimming off all the tabs/protrusions from the J panel.

This a front view of the tach mounting panel I made by cutting/heating/bending some ABS sheet. After installing the tach, it would push the vent panel up, popping it loose, so I heated the large hole in the panel with a torch, and pushed the tach into it, indenting the hole just a little. Then I sanded it a bit with a Dremel, and now the vent panel fits over it tightly, but does not get pushed out of place.

Angled view of the tach mounting panel.

Side view of the tach mounting panel (before indenting).

Panel and tach mounted in dash.

Closeup of tach. Here the tach is mounted upright, but once I viewed it from the driver's seat, the first digit was obscured by the vent panel, so I rotated the tach. The tach is a press fit to it's mounting panel, and the vent panel holds it tight, so to rotate it, I simply popped the vent panel loose, rotated the tach, and pressed the vent panel back down. I also had to slightly trim the bevel in the J panel hole, as it wasn't completely flat to the tach until a little bit of Dremel work was done.

Here it is rotated, with the car on, engine off.

Below is the diagram for locating the tach signal wire. Locating the power/ground wires for the tach is up to you. I grounded the tach to the dash and powered it by tapping into a spare fuse location in the fuse panel, but you can tap into the cigarette lighter/accessory plug or other items.