03 MUSTANG RADIATOR FAN NOT WORKING

Hands down. The EASIEST way to trouble shoot a cooling fan "issue" is to use an ODB2 scanner with bi-directional controls to "command" the fan to run. This offers an easy way to see what is happening by testing for voltage at various points. Create an attack plan based upon what works (high/low speed) and what does not work.

Further. The ODB2 scanner route offers an easy way to find out what the PCM "thinks" the ECT value is as well as what the PCM is commanding the fan to do based upon that value.

Want to know if the ECT is accurate? Then check the ECT after a cold soak. Does it match the outdoor temperature?

Here's some information on an affordable Windows based unit with bi-directional controls. Very advanced graphing capabilities.

ForScan ODB2 scanner w ELM327 USB

If pressing the "easy" button is not for you, the use a test light to find out IF there is power at the fan connector with the AC on. IF there's no power at either of the fan's hot wires it will be necessary to trouble shoot the fan's low speed power circuit.

Next disconnect the fan connector and jump +12 volts from the battery towards the fan using scrape wire. Does the fan work on BOTH speeds? IF not, then the fan is bad. Best to use a fused jumper if you have it.

I always recommend starting every electrical trouble shooting session with a through review of the battery, charging system, and grounds.

Howto perform charging system voltage drop test