1990 GMC wont go on
 

I have a 1990 GMC Sierra 2500 that wont start. Nothing happens when I turn the key. A week ago I took it to get a tune up since it been shutting off on me and needed new wires. It has been working well for the past week and now it gave out on me. The battery has power since the lights go on and the starter was replaced last year. I am starting to get frustrated and just looking for any kind of help. If you had this problem or know what may be causing it please let me know. Just want to put my money in the right place since money is tight right now for me.

I would get a voltmeter and check the battery, should be 12 volts or more. Do the lights dim when trying to start. If battery good then the positive cable from the battery may be bad, it's an in line fuse link. You could check for voltage at the starter with someone trying to start it. Do you hear a click indicating the starter solenoid is working.

I had a similar problem... Meter said 12 vdc and the head lights came on... but there just wasn't enough punch (Amps) left in the battery to turn the engine over anymore.

Confirm this with your truck just by getting another battery from a friend.
Don't boost your truck, replace it with a good battery. This will confirm the fact your truck needs a new battery.