Procedure of r&r of heatercore of a1989 mustang 5.0

SOUNDS TO ME LIKE YOUR TACHO CABLE HAS COME LOOSE, CHECK THE BUILD MANUAL OR THE WEB FOR ITS LOCATION & REMOVAL/REPLACEMENT PROCEDURES

Here is the link to show you the diagram for the fuse box,copy and paste address into address bar then press enter.
http://www.google.com/imgres?imgurl=http://www.allfordmustangs.com/forums/attachments/5-0l-tech/38405d1200851008-1993-ford-mustang-lx-5-0-ho-fuse-box-diagram-mustangfusebox.gif&imgrefurl=http://www.allfordmustangs.com/forums/5-0l-tech/101590-1993-ford-mustang-lx-5-0-ho-fuse-box-diagram.html&h=690&w=480&sz=24&tbnid=3dhE4qaMvt-AaM:&tbnh=269&tbnw=187&prev=/images%3Fq%3D2000%2Bford%2Bmustang%2Bfuse%2Bbox%2Bdiagram&zoom=1&q=2000+ford+mustang+fuse+box+diagram&hl=en&usg=__9b3JW03hcMINM3UU2F5fYMfXo4k=&sa=X&ei=dn6TTeuSBoLG0QGS-v3MBw&ved=0CBcQ9QEwAQ

When was last tune up? Plugs, wires, ALL filters & fluids??? Especially fuel filter. I'd start there and run a good fuel system cleaner through it.

02 mustang 3.8 missing on # 3&5cylinders -replaced plugs & wires & coil 2 times still no fire on 3 & 5

yes. it is located behind the dash board. behind the glove box.

That is normal
Not likely #5 & #8 all the time. Don't go by codes you get. Walk a new coil,until you find bad one

The one line is the supply line, the other is the return line, the other one would most likely be for evap emissions.

how to replace headlamp bulb on a1989 dodge dynasty

sounds like the water line to the heatercore or the heatercore itself may be bad.

First you have to remove the entire dash assy. Once the dash is out then you remove the heater/evaperator box. To remove the box you must first disconnect the heater hoses and the A/C lines from inside the engine compartment, along with a few bolts/screws that hold the box. There may be more bolts/screws holding the box to the firewall inside the car too.(can't remember, too many makes and models.)