Here is a quick outline of how to add an additional light to the toilet. The first step is to find a 12V rated LED light. This is a small one we had laying around.
The next step is to grab some extra wire and splice this wire to that 12V LED. You see below WAGO wire clips which can be found at most hardware stores for ease of splicing. You will want enough length to route to the bottom of the toilet and to the location of your new LED which can be mounted anywhere on the toilet or externally.
Here is a picture below of the toilet "Base cone insert".
Remove this base cone insert from the toilet as well as any mount screws if you have them.
Underneath, you should find our wire cluster. There is a cluster of two yellow wires that come together as shown below.
I found a 3-pin wire connector and unclipped the 2-pin to replace with the 3-pin. Again, usually available at hardware stores but you could also splice wires together however you feel comfortable.
Below is a picture showing that 3-pin connector with the new additional wire for the LED we setup in step 2. This wire happens to be yellow as well. It will get connected into the third spot of the WAGO clip.
Now I will add the new red wire attached to my LED's positive terminal from step 2 and it will connected into the 5-pin red cluster. There should be a free spot open so you won't have to change anything.
You see below the entire setup with my yellow and red pin clusters as well as the LED on the other end of the free wire.
You can test the LED by putting your thumb in front of the sensor.
Below is the LED illuminated with my thumb. It should turn on with my thumb in front of it and off when it is not.
Now you can install the cone insert back on. Be careful to route the wires to the ribs don't crush the wire. You want this base cone insert to sit flat. I routed my wires to the back corner and will zip-tie these wires on to the rest of the harness for aesthetics.
I found this gap in the back corner if I wanted to route my wire externally but in theory you can drill a hole on the right side and mount the led through the plastic there.
