I am looking to buy some new dynamo lights because the (halogen) front light which came with the bike is not bright enough. I have a 2.6W dynamo and was looking at the B&M IQ-XS and the B&M Toplight Flat S. However I just saw the cables coming from the IQ-XS are non-replaceable. This seems to be the case for most lights under 50 euros so I was wondering if you know of any alternatives? I'd like to be able to keep my lights if the cable breaks.
Buy the light you want regardless of whether the input wire is integral.
As long as some stub or remnant of the original wire is intact, you can make it as long as you want in the future by splicing to it with a proper heat-sealed connetion. Meanwhile, the sealed joint between the light and the cord makes failures or issues in the connection area much less likely than if it had spade connectors there.
If you want a light with a seperable cable, there's no shortage of them because most of the basic ones like Herrmans, AXA, Spanninga etc are all like that.
I did the same thing as you're asking, with my ( [Busch u. Müller Lumotec IQ Cyo Premium senso plus 1 ) and the Shimano Nexus dyno, and tail light.
What I did originally was hard wired my dynamo lead end to my front fork, and left about three inches before the top of the fork crown and spliced the two leads +ve/-ve from the B&M light together and soldered them with my gas soldering iron, then insulated both joins with heat shrink on both separate +ve/-ve , then over laid a separate larger head shrink tube covering the two wires along a couple of inches so they're properly insulated. I taped the small amount of excess wire around the inside of fork crown using some black duck tape, since no ones going to be looking and it keeps it nicely out the way. (dont forget to pre-cut the tubing in advance and feed them onto the wires :) )