Good morning, sorry for delay, my name is ***** ***** you for asking your question, I will try and help you out.
Check all your pass through connections on firewall for damage and corrosion. Particularly from ecm to cab harness.
Those signals you are losing come from engine ecm and go into cab for gages,once you loose communication with dash light comes on you loose power and fan comes on for any safety related item, in this case it does not know how hot engine is so default setting turns fan on.
This is a common intermittent problem with no rhyme or reason, I have seen this dozens of times.
Use a good electrical cleaner to remove corrosion and electrical grease on connections to prevent future issues.
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