Custom-fitting antenna mast in 2003 Mitsubishi Diamante LS

The original mast broke, and after searching on many websites for either aftermarket mast or OEM replacement mast, it was apparent that one does not exist (or at least is really hard to find). Even though you can see a replacement mast for $30+ on OEM parts websites, after confirming with a VIN number they tell that the only option is getting a whole new assembly for over $200. The reason might be that this particular mast doesn't have teeth on the white plastic wire. Instead, there is a plastic bump on the end, and the wheel inside the antenna assembly grabs this wire by that bump, so replacement masts might not be available just because of the complexity of the replacement process.

Anyway, I grabbed the cheapest available mast that looked as close as my original one on eBay for $11, it was designed for 94-98 Saab 900 if you are curious.

My first problem was that the old mast broke inside, and I couldn't get it out, so I just cut the aluminum tube of the power antenna in half with a saw. I got all the junk out the tube and inserted the short piece of tube from my new mast, it fit perfectly:

Then I had to cut all the teeth with utility knife since otherwise the cable didn't fit into the groove of the wheel inside the power antenna:

I then used a piece of sandpaper and the existing clamp that's holding wire harness to put pieces of the aluminum tube back together (Hint: draw a straight line along the tube with a black marker before you cut it, otherwise you'll need to spend some time aligning it when you put it back into your car):

Note: teeth aren't cut yet on this picture, this was a test install

Now comes the hardest part: adjusting the length of white wire and up/down switch mechanism. There's a small white wheel that rotates with each half-turn of a big wheel, and it turns a metal plate that connects/disconnects 3 metal contacts for up/down motor movement. You have to cut the white wire so that the contact for going down disconnects just when the antenna fully retracts (Note that there is a moving part inside the big white wheel, it's needed to keep moving to disconnect the contact after antenna is fully retracted, keep that in mind when you're figuring where to cut your wire). This determines the length of your wire up to a half-turn. You can leave it like this or you can cut off several additional half-turns by fully extending your antenna and seeing how many wire you have left.

I had to affix the bump to the end of the wire and install it into the big wheel several times while adjusting the length (you need to make a hole at the end of the wire to insert that metal piece):

Your antenna motor now disconnects after fully retracting. At this point we need to make it stop after it fully extends. Unfortunately, when I fully extended my antenna, there was still contact with the metal on the ring, meaning that the motor will keep trying to pull the antenna up, eventually breaking the wire or failing. So I had to cut a piece of the ring to make the motor stop. I cut it such that the contact plate slides off the ring with the last turn before being fully extended. That means that my antenna will never be fully extended, but that's just about one inch so I don't care.

 Now you can bench-test your antenna with a drill battery or in your car. Black wire connects to negative battery terminal (Ground). Yellow/red wire should be constantly connected to positive terminal. With such a connection, antenna fully retracts and stops. If you, in addition, connect green wire to positive terminal, antenna will fully extend and then stop (power is supplied to this wire when you turn your radio on).

Here is the video of my tests:

Aside from a piece of sandpaper, a drill battery, and an awl to make that hole in the wire, I used the following tools:

 and this is the leftover junk :)...

Hope that helped, and if you have any questions, feel free to ask.