Check charge system

You mean with the engine running? If the engine is running, the heater fan should be getting power from the alternator, not the battery. Does your battery light go off after engine is running? Or does the voltage gauge show normal charging when running?
If you can start the truck, have your charging system checked out. If it won't start now, have the battery charged up and try again. Then have the charging system checked. If it is good, your heater fan may have a short and drawing too much current, But a heater fan will run the battery down pretty quick, if the engine is not running.

You would need to check the wiring and fuses to see if anything is blown or melted. The warning light is for both hydraulic brakes and the charging system.
In your case the light probably came on because the alternator stopped charging the battery.

Check batry terminals are secure & free from corosion, check security of earth strap to engine & main power wire on starter, if ok have the batry load tested to ensure it can perform under load as the starter needs a lot of current. Have you tried a jump start?

check charging system like altenator or make sure battery cables are clean and tight. go to advance or autozone they will check it for free.

have you tried cleaning the batt terminals and make sure the plug on alt is in and the bolt that holds the one wire is tight in the alt

Sounds like battery not holding charge. Or a light staying on, boot or glovebox? Most likely battery tho.

If the vehicle is not even running or begins to die after as you say an hour that means you still have a charging problem. basically the only reason the battery is there is to start the vehicle. The alternator/charging system is what runs the electrical system in the vehicle. In the power distribution box (a fancy name for a fuse box) under the hood of the vehicle there is a fuse for your charging system. Below is a picture of the layout of the fuses in the panel under the hood of the vehicle in the engine compartment. I marked the fuse you need to check. It's a 15 amp fuse and will cause the same thing as if the alternator was bad. I hope this helps.

Get the battery & the alternator checked (Autozone, O'reilly's or even Pep Boys can do that for free). If the alternator is out or going out, it's not charging your battery - that means everything electrical in your car is now trying to run directly off the battery & draining it (it doesn't take long - especially if the lights or A/C is on). If those check out ok, take it into a mechanic & have them run a diagnostic - you may have a relay out. Good Luck.

Go to web site WWW.HMASERVICE.COM and register your vehicle by VIN #. You'll then have access to shop manuals, wiring diagrams, technical service bulletins, illustrations, etc.
Provided there is no problem with the vehicle's wiring, find out what the charging current is to the battery. I've seen batteries which TEST good, but when under a CHARGE short out internally.
Example: Tested a battery & charging system on a Hyundai Elantra, the battery tested "Healthy" but indicated there was a CHARGING SYSTEM PROBLEM. I checked the battery voltage while the engine was running and found the battery voltage at 14.3 VDC (which was normal). I then used a Digital DC Clamp meter arount the positive (+) battery cable & found the battery was charging at 70 Amps!.. it was supposidly already fully charged (should have only been taking 4 to 6 amps when fully charged).

Best guess without looking/diagnosing the vehicle myself

Maybe this will help.

CHECK ALTERNATOR 175 AMP MEGA FUSE. AND CHECK ALTERNATOR 20 AMP INLINE FUSE.IF FUSES OKAY.REPLACE BATTERY CABLES AND CHECK ALTERNATOR BATTERY FEED WIRE AND VOLTAGE REGULATOR WIRES FOR DAMAGE.AND CHECK DRIVE TENSION.MAKE SURE DRIVE BELT NOT DAMAGE OR SLIPPING.