I have a Secula Plus but I did not mount it on a fender (mudguard), it is a great light. I have the fender version but I made a bracket to mount it on a rack instead.
Here is a thread I started on hiding the wires for a taillight. Several others added comments.
http://thorncyclesforum.co.uk/index.php?topic=12775.0I used the tile sealant that was discussed in that thread, it worked great. It was messy, I used some disposable gloves. And I bought a lot of cheap clothes pins to use to hold the wire on the sealant until it hardened up. I let it sit to harden up for a couple weeks, I did not want to risk removing the pins and using it sooner. I ran the wires under the fender off to one side, not down the middle. I did not get any of the sealant on the outside of the fender, but that is a risk so you should have plenty of wipes handy.
To make it easier to remove the fender from the frame, I added some quick connectors where the wires come out of the fender, the quick connectors are above the bottom bracket. Thus, the wire along the downtube can be separated from the wires under the fender.
I have no photos at this time. Sorry.
I drilled two holes through the fender for mounting the light, the wires pass through one hole and the light bolt passes through the other. You have to be careful you do not get the light too high or too low on the fender or the light will aim upwards or downwards. I could not mount mine exactly where I wanted it because of a fender bracket was there, but I was pretty close to getting it where I wanted it.