Security light is on and truck wont start. It does this once in a while. How do I fix this?

First, clean off the contacts in the black security resistor spot on your key (one metal strip on each side of the key). If you use soap and water, rinse and dry thoroughly; otherwise use rubbing alcohol. Avoid touching these contacts with bare fingers; skin oil buildup can cause this problem.

Second, spray a lubricating-type electrical contact cleaner into the lock, but try to keep it in the area where the resistor spot goes (a non-lubricating type could cause problems with the mechanical part of the lock). Run the key in and out of the lock several times, wipe it clean, and spray the lock again. Never squirt a graphite-type lock lubricant into ignition locks with this type of security system - the graphite could create a current leakage path around the key and cause a false security alert just as poor connections would (if this is the problem, the surest fix is to disassemble the lock and clean the graphite out of the contact area, although contact cleaner may rinse the offending material into the mechanism where it was intended to go).