Iwouldn't go crazy hunting it down. If necessary, just run another fused 12 volt line. I believe the Magnadyne has a fuse built into the chassis of the radio (external).
You should also know that a Magnadyne from that era had issues with the CD skipping. The problem was a bad connector at the rear of the radio. The 12 volt connector didn't make good contact and people went through dozens of these radios before Magnadyne finally figured out the problem in about 2006 or 2007.
If you do a search, you of the entire forum, you should find some info on the bad connector.
Don & Mary
2014 Newmar Dutch Star - All Electric - 450 ISL
2016 GMC Canyon 4WD Crew Cab