1991 g10 chevy van

I have an aftermarket deck that has worked perfectly for the three years it has been installed. The other day it lost power while driving. I took it out and located the 12v power wire and traced it back to where it directly plugs into the fuse box.
The actual radio fuse is not blown and has power when the key is turned (small 10A fuse on the deck itself is also fine). However, the wire that directly runs from the unlabeled single pronged port in the fuse box to the power wire of the aftermarket wiring harness does not have any power when the key is turned (confirmed to be the same wire by visual trace and continuity test).

The next step I could imagine would be to take the fuse box off the firewall and see if there is something going wrong from behind it. Could there be another solution before I go through that process?

I guess a second question is why is there a direct unfused wire to the radio as well as a radio fuse? Two different operations?

Thanks!

 

There are 2 power wires going to a radio. Both are fused, but could be by different fuses. One is hot all the time and one is hot when the key is turned on. The one that is hot all the time is to keep the memory in the radio when the it is turned off. You should never have a circuit which is not protected by a fuse.

 

Yup. The memory circuit fuse is prob 1 amp. It only needs 0.3 amps or so for the memory. The 10 amp is the main power fuse.
Check the fuses around the block. Maybe something unrelated blew and that powered that prong you mentioned. Add a fuse to it while fixing it.
If necc get power elsewhere. It must be hot key off, not key on.

 

Thanks for the responses. So as oldchevy said, you should never have a circuit that isn't protected by a fuse. So in the case of power wire the runs directly from the wiring harness to the fuse box, it may be using a fuse lower down the fuse block, such as the horn fuse (that happens to have a short somewhere and keeps blowing). Because this fuse is blown, the port with the power wire above is not getting power?