Mazda Repair Questions? Ask Mechanics for Answers ASAP
You have several problems!
1) Dome light / Door ajar light - One of the door ajar switches is sticking in the latch. What I usually do as a cheap first fix is to spray each latch with brake parts cleaner. Then open and close the door about 10-12 times. Then spray the latch down with WD40 and again open and close the door about 10-12 times. This usually frees up the stuck switch and sometimes the cleaning lasts a year or more! Otherwise you will need to replace the switch in the door.
2) A/C compressor kicking on.... this is normal if the A/C is turned on OR if the ANY mode that uses the defroster is selected. Normal operation and should be plugged back in to ensure long life of the A/C system.
3)Oil pressure gauge going wacky is typically the oil pressure sending unit. You may also notice that oil has started dripping from it. It's a small inexpensive sensor/switch that screws into the engine with a wire attached to it.
4)Chime - Probably caused by the truck thinking the door is open with the key in the ignition. Try checking to see if it makes the noise when the dome light/door ajar light are working properly.
5)Blower only working on high is most likely a bad blower motor resistor. The high speed setting completely bypasses this resistor but all of the lower speeds must go through it. One bad section in the resistor and all of the low speeds can stop.