Here is a 2003 Dodge Ram with a faulty ignition switch.
The Switch runs multiple components one of which is the heater/ A/C blower fan.
The high current passing through the ignition switch causes excessive heating on the contacts and connector spade making a poor connection.
This is a common issue.
It might even be a recall for your vehicle.
Replacing the switch is relatively simple and less than 30 dollars US.
This new switch fixed the intermittent or non-working blower fan.
2003 Dodge Ram Intermittent A/C Blower Replace Ignition Switch