Step 1: Materials and Tools
You will need to buy a switching 3.5mm (1/8") female headphone jack. The important part is a switching style like the one from mouser below. It should have 5 contact points Left + in and out, Right + in and out, and ground. We need it to be switching style because we want to still use the internal mic when one is not plugged in, but switch to external only when one is plugged in. I recommend getting this one or the one just like it with threaded bushing .
You also need about 2" of 2 conductor wire about 18 - 22 guage.
small screwdrivers flat and phillips
small file (not shown)
Step 2: Remove the Screws
There are 8 screws required to open the camera. Each side has 2, the bottom has 3 and inside is one silver screw that you must remove. I recommend starting on one side and working your way to the other side removing each one in order and keeping track of the order. You might try putting a piece of tape sticky side up on your table to keep the screws in the right order. This is important because they are all different sizes.
Now remove the smaller left side piece of plastic. Under there is a small silver screw which you need to remove to take the back off.
Step 3: Remove the Back
Once it is loose carefully fold it down to show the one ribbon cable you must undo. Undo the ribbon cable by flipping the hinge 90 degrees from the bottom of the camera to straight out.
Step 4: Test Fit and Drill
You have a chose to either have the jack flush to the inside of the plastic held in place with epoxy or more securely screwed in place from the outside. I decided that it would look much better if there was nothing on the outside of the camera but a hole. So i drilled a 3.5mm hole which is just big enough to fit the connector through.
Once the hole is drilled make sure that you can securely fit your connector throught the hole and it sits well in the jack. I had to remove some of the metal on my jack with a hack saw so that the connector could fit after going through the camera body.
Step 5: More Test Fitting
You have to remove plastic from the small side piece and from the back piece to get everything to fit right.
On the side of the back of the camera piece you need to remove the material so it look like mine does now. These are where it used to screw into the metal piece that you removed. However it still will screw in on this side through the screw you can see from the outside.
Test fit them together off the camera to make sure it will all line up correctly
Once you have it where you think it is good epoxy the jack to the side plastic piece and let it cure for at least 12 hours. My epoxy set fast but wasn't strong enough to take the pulling in and out for 12 hours. Once it was dry I again was test fitting and removing epoxy until I was satisfied that everything lined up well.
Step 6: Wiring
Test your connections with the multimeter to determine which points are for straight through when not connected and which ones are to the external when connected. I used 3.5mm male to male cable plugged into my jack to verify where I needed to solder the connections. Remember the Ti1/500d is only mono capable so one set (either left or right) will not be used. The black wires from both sides will be soldered together to the contact that is connected to the outside metal ring.
Step 7: Finish
That should be it test it out before screwing it all back together.