Let's treat these as separate problems.
On the horn. Put power and ground directly to the horn itself and see if it works.
On the dome light. Switches are pretty common on these and worse yet new have been found to be defective. What I would do Is get some thin lubricant like wd-40 and spray the latches thoroughly and open and close the doors 20 times or so to work the latch. That may take care of the dome light problem, but if it doesn't a scanner will be needed to work the door ajar switches to determine the bad one.
On the Blower motor. I think two problems may exist on this. One the resistor is likley bad. The high speed goes separate from the resistor. The resistor just modifies the electrical output to the motor to slow the motor speed down.
On the battery drain or draw. Since the blower stays on high with the ignition switch off, this is probably the circuit that has the draw.
I am going to get you diagrams and send them to your email.
Friday, November 27th, 2009 AT 6:59 AM