did it work? Just wondering for future install...
It did! The idea was genius.
Sorry about the delay, I was quite busy lately and only got to try it last weekend.
Here's some insight from personal experience:
1. The holes for the headrest have metal guide rods, which are open ended and push into the back seat foam.
2. You can stick a (solid, hard) wire through the guides all the way down, if you push carefully you won't poke the foam but slide between the foam end the metal seat plate.
3. Since the metal plate is bent at the bottom, you'll have to stick your hand between the foam and the plate to find the hard wire - shouldn't be far inside if you pushed it enough.
From here, you can attach whatever you want to the hard wire and pull it from the bottom.
Now, the caveats and warnings:
1. The metal plate is SHARP on the inside. And since the foam is pushing up against it, sticking your hand between the foam and the plate should be done very carefully (especially when twisting or pulling your hand back out). I managed to scrape my skin several times.
2. The metal plate is not flat - it has some indentions inside, to which the foam is cut to shape. I assume those are to make the plate sturdy. Anyway, because of those, the hard wire might not be as easy to push through all the way down. Also, putting wiring inside might disturb the way the foam matches the metal plate.
3. Once you stick the hard wire through the holes and guides, there might not be enough room left for whatever you are actually trying to get through. In my case, the headrest wires have connectors at the end which are almost as big as the hole itself, and it was a very tight fit once the hard wire was also in there.
4. The guide rods are sharp as well. If you decide that you need to get the headrest wire back out (for instance because you forgot to slide some plastic part onto it first), DO NOT PULL ON THE WIRE. It will strip the insulation and, if you keep insisting, it will cut through the actual wires inside. Those are usually thin enough that you will need to solder them under a microscope, or get new wires altogether.
5. Speaking of plastic parts - the headrest has a round rod and a "marked" rod, which is useful for height stops. Matching that are two little round plastic parts you should have saved from the original headrest. One has a push-in mechanism to release the spring and raise or lower the headrest. Make sure you slide those plastic parts MATCHING the rods, onto the new headrest's rods BEFORE inserting the wires in the seat. I swapped the two parts out accidentally and realized too late. And yes, I stripped the wire when pulling it out.
6. If your arm is just the right combination of long, thin and strong, you don't need a hard wire. In fact, I found it easier this way: insert headrest wires in the whole until they hit the foam (at the bottom of the metal guides). Then, stick your hand from the bottom of the seat, between the metal plate and the foam. With some insistence, you will be able to reach all the way up to where the guide rods end, grab the wire and pull it down. Same thing for the other rod, if you need to pull two wires.
7. Unless you're good at fishing wires and inserting metal rods at the same time, plan on having somebody to help you with actually inserting the headrest in the guides while you're fishing both wires at the same time from the inside of the seat (assuming both headrest rods have wires sticking out, as was my case).
Hope this helps. If there is interest, I may also post some drawings to illustrate all of this.
