Tried to start the truck---nothing happened....the ignition key was turned on but nothing. 3 days ago, same thing happened I turned key and nothing. So what I did---turned key on till red light came on (but did not turn key on all the way). I left it on for 10 minutes ---came back and the truck started. What did the leaving ignition key on 1/2 way for 10 minutes do? Did it warm up solenoid? Did it heat up starter? Now same problem. tried same thing put key and turned it 1/2 way, but this time nothing ---truck wont start.

i suspect either the ignition switch is worn out or the starter.
test the starter first then the ignition switch. both are fairly easy to replace and not too costly. if you are a diy person then do a screw driver starter test. This will determine if the starter works and usually how well. I buy the starter rebuild kits online for $35. The ignition switch is also around the same price and easier to change than the starter. The ignition switch is accessed by removing the lower steering column cover then the two screws for the upper cover. Then unplug the ignition switch then remove the holding screw. sometimes the wiring is taped up carefully remove the tape. when installing the new switch make sure the key is out so that the new switch will align correctly

repeat

I just went through this two days ago. You probably need a new ignition. What happens is these cars lose connection for some reason to the chip in the key and it can't be fixed with just programming. It has to be a whole new ignition. Mercedes are so much different then to any American car. Good luck and it costed around 950 to fix in Wa state.

check the main engine fuse in the engine compartment

Thanks for choosing FixYa and welcome.

You didnt list the type of car this is, the most common thing that causes this is the starter, i just had a saturn, the customer had the same problem we told her it may be the starter but cant be 100% sure until it actted up, she didnt want to replace it unless we were sure, so we kept and drove the car around for 5 days and finally the last day it didnt start and it was the starter , same problem turn key and nothing no noise and no start, i would have the starter replaced and go from there, its a mater of time before the car just wont start,hope this is helpful.

the ignition switch is a very common problem with these vehicles. when the problem is occuring check the pink wire coming off the ignition switch and see if there is power. the computer controls the starter on this vehicle and if there is insuficient voltage going to the ecu it will not power up.

Not all replacement parts are good. I would guess that the new ignition switch is bad. Its also possible that the wiring harness is loose where its connected to the ignition switch. You could try jiggling the wires.

It could be the park/neutral switch, next time it doesn't start try wiggling the shifter in park while turning the key, or shift to neutral and see if that will work. if that doesn't change the problem I would replace the ignition switch.

I suspect the ignition switch is malfunctioning.