Fuse used for stock double din cd/cassette player? Options

[Starcraftjunkie]

Hi,

I'm wondering someone can help me with a fuse issue I've been having after putting in a stock toyota double din stereo.

In the fuse panel under the hood (and on the otherside of the ruse panel, there's a legend of some sort):

10A - Dome
15A - Clock or something
20A - Radio 1
??? - n/a

I'm just wondering if everyone has a fuse in that 4th slot. There's no amp markings on the fuse (and not due to wear and tear. It's just not there). Can anyone first clarify what does that 4th slot do?

Also, for those of you with a double din stock radio, do those fuse ratings match yours? I'm asking because my dome fuse just blows everytime I turn on the stereo. There's no extra wires grounding themselves out (just using the stock toyota harness).

So right now, it's either I drive with music, or I drive with door lights/dome light/low beams only.
When the 10A dome fuse blows, the car runs only the daytime running lights in the high, or both low/high on at the same time. I suppose it's a way of telling the driver something electrical is amiss.

Help please! I've already gone through 4 fuses checking for grounds and stuff.