E4500 odd issue starting truck - what's wrong ??

[GM GR]

this is 'odd' to me; I cannot give an explanation - got an idea why? :

 

The battery gauge read fully charged today, but still a 'no start' at turn of key.

so I  'fiddled' with lights to see if they dimmed while turning key... - didn't appear to.

The parking lights were left on (unintentionally, but nevertheless...)

while I went into the house for 10 minutes or so.  I tried to start the truck again when I returned.

It started !!

 

that is 'odd' - what in the world - why ??

 

The entire thing was repeated when I returned home tonight.  The truck did not start. I left on the parking lights for 10 minutes

after which the truck was successfully started. .. huh ? 

 

What IS that ?  (what am I 'really' doing ?).....   do you have any idea, perchance ?

 

[CamGTP]

Not really the section for talking problems about a E4500 but anyways.

 

Check and clean all your power/grounds from the battery to the frame and down to the starter.