I am doing a radio relocate, adding trustz gauge overlays to my cluster, and adding boost, oil pressure, and wbo2 gauges. After initial install and testing of cluster & gauges and redoing the existing Alpine radio harness from PO (wire nuts were used instead of crimps/soldering... derp) I suddenly had no clock, no radio, and no overhead interior lights.

I went through and tested my wires for good connections and even broke out the multimeter, which I'm not very familiar with, in an attempt to figure out what was going on.

I had 12v switched power through the radio harness just fine, I have a ground for the gauges and radio that was good, but my 12v constant was reading very low. I went to the OEM harness plug and got a reading that was also very low.

My next thought was to check for fuses. After exploring the fuse box for the first time I found the radio and interior light fuses under the hood. The radio fuse was fine. The interior light fuse was popped. I replaced the 10 interior light fuse and POOF I had everything back including the radio :/

Q: Not sure why the interior light fuse would affect the radio???

I'm a novice with electrical but after a few hours I had everything wired and functional. Just waiting to get a bung welded in for my wbo2 to read correctly.

TL;DR-no interior lights, no clock, no radio... radio fuse was ok, interior light fuse was blown. Replaced it and everything works. Why?