1991 Chevy Silverado the heater is not working need the location of the heater fuse. So many wires don't know which ones goes to heater can you help

Anrez, your 1991 Chevy trucks O2 sensor could be located in the Y pipe just ahead of converter or in the front portion of the converter.
Check the attached links,instruction and guides, Good luck
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if you are having fuel pumo problems, its most likely the fuel pump

Actuator on front axle not working or unplugged ,,

which engine

Do you know what a automotive electrrical wiring diagram is ? How to use a DMM- digital multi-meter ? Pick one system an diagnose an you will probably fix all the syatems . Voltage drop testing . Voltage or ground side problem .
Mastering Voltage Drop Testing with Pete Meier and Jerry Truglia
Free wiring diagrams http://www.bbbind.com/free-tsb Enter vehicle info. year , make , model an engine size. View wiring diagrams an test the circuits.

The yellow wire from the truck attaches to the red wire of the stereo. The black wire goes to the black wire. If the truck doesn't have a black wire, connect the black wire from the stereo to a bolt on the frame of the dash. The orange wire from the truck goes to the yellow wire of the stereo. Please let me know if you have more questions.

1991 Chevrolet Silverado C1500 Car Audio Wiring Schematic
Car Radio Battery Constant 12v+ Wire: Orange
Car Radio Accessory Switched 12v+ Wire: Yellow
Car Radio Ground Wire: Black
Car Radio Illumination Wire: Gray
Car Stereo Dimmer Wire: Brown
Car Stereo Antenna Trigger Wire: N/A
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: N/A
Car Audio Front Speakers Size: N/A
Car Audio Front Speakers Location: N/A
Left Front Speaker Positive Wire (+): Tan
Left Front Speaker Negative Wire (-): Gray
Right Front Speaker Positive Wire (+): Light Green
Right Front Speaker Negative Wire (-): Dark Green
Car Audio Rear Speakers Size: N/A
Car Audio Rear Speakers Location: N/A
Left Rear Speaker Positive Wire (+): Brown
Left Rear Speaker Negative Wire (-): Yellow
Right Rear Speaker Positive Wire (+): Dark Blue
Right Rear Speaker Negative Wire (-): Light Blue

there is a resistor that controlls the speed of the fan and you have to replace it it is located where the plug goes to the fan motor it should have two plugs in it one from the controlls the other goes from the resistor to the fan it is a dealer only item it costs around 89 dollars check different dealerships if you have more than one close by the price will vary my 2006 chevy silverado work truck lost the 1 and 2 speeds then others and it was freezing out and i replaced it and have not had any problems since inspect the wires i had two wires and one part of the plug melted on mine went to junk yard and got a new plugg for under ten bucks dealer wanted 117 dollars

mcdevito75 here, I really don"t know, even if there are manufacturers torque specs. I myself just make the nut very tight, remember the steering wheel goes onto the steering shaft which is tapered.

your speed switch located in heater box usually one wire to it in passenger feet area above "TOES" usually you loose 1 or 2 speeds on fan but it is unplugged or completely cooked good luck!

On the inside of the panel that you take off to get to the fusebox there should be a diagram listing what each fuse controls. Try that and see if it works. If not a chevy dealer can always help you