Can this be due to a bad IAT sensor?

are you seeing a voltage drop on your dash when the light it on?

 

Does the truck run?

No voltage drop, 14.6.

Runs fine. Just had my buddy install a used vp44 due to a p0216 code.

If you want to verify the IAT use a live data tool and see the actual IAT temp and see if it showing a normal number.

 

Note: Even with a IAT sensor missing it the wait to start light should cycle normal and go off.

 

So this points to a internal ECM problem which could be caused by a bad alternator with high AC noise issues.

Could be the ECM. Previous owner installed an on/off switch to control the alternator because the PCM was over charging it. Who knows how much damage was done before I got the truck. The light was missing and I replaced it and functioned normally for awhile. Installed an internally regulated alternator and charges fine now. AC measures. 07 volts at the alternator with all accessories on.

I am gonna go out on a limb and say it is time for a PCM, ECM, and Alternator.

AC measures. 07 volts at the alternator with all accessories on.

 

Too high... Alternator is failed. it should be 0.01 to 0.02 normally full loaded. Anything over 0.05 will cause mild issues. Anything over 0.10 is damaging...