Installing Air Horns in a MKII MR2
WARNING: This page is meant to be a guideline only. Individual experiences vary. Any time you work on a car, you risk damaging it...if you damage your car while installing the horns, don't blame me, ok?! ;>
The horns sound great though...no delay at ALL (I was worried there would be, with a compressor and all)...VERY loud! I owe a lot of this to Troy Pummill though ('94T)...he installed air horns first, and I had the chance to learn from his experiences before attempting this myself! Troy installed the compressor in a different location than I; I think my solution protects the compressor from the environment better and will contain it in case the adhesive fails - so the compressor doesn't go bouncing down the road! ;>
What you'll need:
Air Horns, consisting of:
Tools:
Other
Prepare the air trumpets for installation
There's a very smooth, flat surface on the backside of the bumper - stick your hand up through the grill and you can feel it. This is what I attached the air trumpets to. But first things first. Open the front trunk. You need to remove the blackplastic radaiator cover. Pull the rubber gasket off at the top of the cover (slides on/off). Now deal with the black plastic fasteners holding the cover in place. Use the small flathead screwdrive to depress the center plastic piece of each fastener, but not TOO much - you can push it all the way through. Once the center is depressed, you can pull each fastener out (to reinstall, pull the center piece up, then install it in the hole, and push the center piece to be flush with the base). Now, removing the cover is tricky...you need to slide it towards the front of the car, while flexing it as needed to clear the hood latch mechanism. I recommend putting rags or a towel between the black piece and the front bumper fascia.
Once the radiator cover is removed, you might be able to get a better view of where you'll be mounting the air trumpets. There's a steel bar - your bumper really - running across the front of the car inside there; it's about 4" tall so provides a great mounting surface. Clean the surface thoroughly with the rubbing alcohol...then clean it again. Test fit the air trumpets...you actually have a lot of room to move them around in there, up and down and side to side, so figure out what you want. The trumpets need to be inserted/fed through the front grill...it can be done, trust me.
WARNING: the air tubing provided will most likely be extremely short; mount the trumpets as far right as possible (as viewed from the front of the car).
At this point the air trumpets have NOT been installed, you've just placed them in there to get an idea of how everything will fit together.
Wiring
This is easy. The factory horns are up inside the grill, one each side, near the top. Little round things. Unplug the wire from each. Now, look at it from above, near the radiator, right side...find the wire that was leading to the driver's side (US) horn and splice into that with a decent length of wire (to be trimmed later). This will be the +12V for the air compressor. The air compressor ground may go to any bolt you choose. Anywhere that a wire passes near a piece of metal, thru a hole, or whatever, you must protect if from abrasion. Use a grommet, tie wrap it in place to something else, or wrap it with electricians tape, depending on the situation.
Compressor
This is...not so easy. The best place to locate it is below the headlight. There's a large area directly underneath the headlight that's pretty much empty; this is where I mounted the air compressor. Now, how the heck do you get to it, you ask? Well, there are two ways.
Method 1: I think the easiest way would be to jack up the LF wheel (use jackstands to support the car in case the jack fails!). Remove the large black cover underneath the car running the full width of it; it's directly behind the front airdam and is roughly 1.5' by 6'. It's held on with numerous bolts and is actually quite easy to remove. Note, if you have the headlamp raised it'll make it easier to see what you're doing once you remove the cover. Ok, so the cover's off, you should be able to see up into the compartment I'm talking about. Raise and lower the headlight a few times to get an idea of what space is available to mount stuff. I chose a surface that, when viewed from above the car, is on the left side of the compartment...find a smooth metal surface.
Method 2: remove the headlight assembly (this is what I did). Remove the headlight itself, then the whole headlight mechanism; it's held on with 4(?) bolts and will just swing out of the way once removed; you don't need to disconnect the wiring. Kinda fun to do too. Mark the position of the top bolts as it appears to be adjustable here.
To mount the compressor, clean the mounting surface with the alcohol very well. Now, you'll want to secure two of those adhesive backed wire tie mounts to the compressor - in my case, I had to drill a hole in the compressor mounting tab to mount the second wire tie perpendicular to the first (I know, I should've taken pictures!!!). Snug them down now; once installed they won't be coming off (you hope). (note, you can also drill holes into your car at some point for a more secure mounting method).
Now, before actually sticking the mounting tabs to the car, install the air tubing as required, to make sure it'll be long enough and that you actually can mount the things where you want to. Route the tubing and wires. if you like it, great! Now, remove the adhesive's backing from the compressoor mounts and press it firmly against the mounting surface (don't forget to clean the surface with the alcohol!). Press and hold for a few seconds (it's best if the wires and air hose are attached to the compressor while you do this so you don't have to disturb it later). Follow the manufacturer's directions on the orientation of the compressor. Failure to do so may result in the compressor exploding (just kidding)!
Now, clean the mounting surface for the air trumpets *again* (clean is good), remove the adhesive backing, and install them in place, pressing firmly once you're sure they're in the right spot. Again, tighten the wire tie on each trumpet before slipping them up into the area behind the bumper; you'll never get to them up there. Don't tighten the wire tie completely or you'll never get the adhesive thingee to sit flush. I didn't use the mounting tabs on the air horns, I just wrapped the wire tie around the horn body itself and made it tight enough that it can't slip out. It's best to have all air hoses attached before doing this though they CAN be attached later.
IMPORTANT: The adhesive used with these wire tie mounts will take some time to cure completely. I recommend not driving your car for at least 12 hours if possible. Not a really big deal, but it wouldn't hurt. If you DO drive it immediately, just try to take it easy, don't corner too fast or anything. One user had the compressor fall off; you may want to consider drilling some holes for a more secure compressor installation (I've had no trouble with mine). The trumpets are light enough that the adhesive works great.