When I got my "new to me" 2003 Legacy recently it would often not start when I turned the key. It would only go click and then do nothing.
I have had this problem before on my 1999 Agco Allis 2025 (Legacy clone) as described over here
At that time I got some help from Brad who had found that the solenoid that shifts the gear on the starter is likely not getting enough voltage. This is caused by the high amperage draw (I measured 15-20 A) through a small wire that goes through multiple safety relays.

Brad recently made a detailed instruction on how to do it which is posted here.

So I was armed with the knowledge on how to fix the issue and figured I would document my installation.
As emphasized in the Tech Forum, this does not bypass any safety features, is fully reversible and has no ill effects on the tractor.

First off here are the materials needed for it. They ran me approx $ 12 (not including the electrical pliers)


Here is the wiring diagram showing the connections needed for the relay.


Since I had the Agco already done I eye balled up the length of the wires and crimped the ends on as shown.


Now on to the actual installation on the tractor. Safety first - so disconnect the negative cable from the battery


Here is the original setup on the starter with the solenoid shifter


The first step is to move the red spade connector from the solenoid shifter


To the new relay


Mount the relay in a good location. The Kohler Command engines has a shroud screw that is conveniently located


Connect the positive cable for the relay to the positive post on the starter


And slide the rubber boot over the two cables to protect them


Connect the new wire from the relay to the starter solenoid


Connect the ground wire to the grounding bolt on the engine. I have one connector there already for my oil temperature sensor


Insert a fuse in the fuse holder (25 or 30 A fuse)


This is what the finished result looks like


Hook up the negative cable to the battery


Then turn the key and enjoy that the starter will now spin every time :thThumbsU