Truck runs good until i turn the heater blower switch on then it wants to stall out what could it be

You don't give much info, so it's hard to give you a good answer. Do you have power up to the heater switch and after turning the heater switch to the on position do you have power to the blower? Did you check the fuses, do you have power on both sides of the fuse? if you do follow that wire and check for power at the other end of it. Some cars have a temperature sensor and the blower will not come on until the temp. is warm enough so that the blower will not blow cold air. If you track the hot lead from the fuse box to the switch, through the switch and to the blower and at any point find you no longer have power, that would be the component I would think is causing your problem. You can also check the blower by running a test lead from the positive side of the battery to the blower motor and see if it runs.

check battery voltage or try skin the ground wire of blower motor and place a jumper between ground wire of blower motor wire and a good ground on engine
if with a good ground the engine don't stall then it was the ground find out where is the ground to
it could be a common ground with other component

you should make a diagnostic to know what happened to your car
of course you need an auto diagnostic tool : http://www.chinasnoy.comand you can find all kinds of tools in chinasinoy.com

I would venture to say that if you hit the dash and the motor started running then the problem would be in the heater control assembly mounted in the dash, like bad wire to Heater switch connection. A bad connection can jenerate a lot of heat and start melting things unless you find the problem soon enough. The switch may already be damaged inspect switches and wireing for any vissible damage and replace as required. However if everything looks ok with the heater control assembly, Their are a few more things you can check to be sure of before relpacing the heater blower motor. Turn the heater controles to the high heat and fan on high as well, settings and remove the heater blower motor pig tail and check to see if power is getting to the motor,( use a 12 volt test light at the wire harness side of this connection ) also check for power going to and leaving the blower motor resistor assembly ( mounted to the side or top of the blower motor housing ). If so equipped. If you find no power getting to the motor at this point then you will half to start working your way back through the wireing towords the heater controles until you find the problem. Using your test light. Now if you did have power going to the motor then replace the motor. Good Luck From Ernie @ RedDeer, Alberta, Canada.

if you are talking about the engine electric cooling fan..it will run after car is turned off until temp goes down then it shut off..unless you're talking about the heater blower motor..then i would look in the engine compartment passenger side firewall for the heater box ..on the box there is speed control resistor for the heater fan speed..that might be shorted.if not fan switch on dash..give more info next time..it makes it easier answer with more info

make sure fan fuse is good, remove power wire going to blower motor then run a power wire to the blower motor from the battery install a an inline fuse in that wire from battery , if it runs with direct power then may be a resistor or switch, remove direct power wire reconnect orginal power wire to motor turn switch to blower on, use a test light see if you have power at motor with switch on, if theres power then motors no good, hope this helps.

HAVE BATTERY VOLTAGE CHECKED.MAKE SURE BATTERY IS FULLY CHARGED IT SHOULD BE 12.5 VOLTS.IF YOU HAVE DIM TURN SIGNAL LIGHTS.EITHER YOU HAVE WRONG BULBS OR POOR GROUND ALSO THE WEAK BATTERY OR UNDERCHARGING PROBLEMS HAVE ALTERNATOR CHECK OUT. FOR THE BLOWER MOTOR.CHECK FUSE AND RELAY. IF BOTH GOOD YOU HAVE A FAULTY AC + HEATER CONTROL SWITCH.OR THE BLOWER MOTOR IS FAULTY.REMOVE BLOWER MOTOR HOT WIRE IT USING A JUMPER WIRE TO BATTERY.IF IT RUN YOU HAVE SWITCH OR WIRES TO SWITCH PROBLEMS. IF BLOWER MOTOR DONT RUN.REPLACE IT AND BLOWER MOTOR RESISTOR.NOW IF WIPERS KEEP WORKING WHEN YOU TURN THEM OFF.YOU HAVE A FAULTY SWITCH OR DEFECTIVE LIMIT SWITCH IN THE MOTOR.

Should have a blower control unit. Sometinmes these are known to leave the blower running on low speed with the key off.

You have clean the blower unit , may be its dirty then . and then check the blower resistor unit for malfunction.

sounds like the heater is drawing down the battery. Which would be a battery or alternator problem most likely. If not check the amp draw of the blower motor .