Radio sometimes works

Keeping it as simple as possible, sounds to me like there is a fault in the wire itself, test the radio by using different speakers and wire.
There is also a fuse or 2 behind the radio (built in) and they sometimes blow, the sporadic working speaker can be a symptom of a slow-blow fuse going. Hope this helps..

You seem to have a short in that fused system. Think back to when this problem started, did you have some work done such as a new radio, or a power antenna, or maybe speakers. If this brings something to mind those items should be checked. GOOD LUCK FRIEND.

I think the Fuse melted away and is blown .

Sounds like someone shorted the wires...you need to look into the entire butcher job and see what wires were touched. Disconnect everything the butcher did and then see if your battery is still drainning power.

It sounds like the brushes on armature for (blower motor ) are worn. Sometime a bad spot on the armature from not being used often and also by being in the engine compartment where it is exposed to condensation. When the brushes stop at that particular spot, the blower will not start spin process unless it draws alot of current that may be why the fuse blew. You can remove the blower and examine or just make the change.

somewhere you have a short in your wires that triggers the fuse in your radio

The radio it's self

You need to remove it, and take it
to a shop that repairs car radios

You don't say how old the truck is - or how old the pump is - most likely it is the pump 'dying' as you try it -

I would look near the tank and find the ground wire -[ it may be on top of the tank] - the most common fix is the fuel pump and sadly it sounds like this is it --

Also - Take down the Vin # and call the local dealer - - ask about recalls and Service bulletins.

My van radio runs on 2 different fuses- both in the fuse box under the dash. One runs the lights the other the sound. Hope this helps.