I have a 85 22r extracab auto 2wd. when i bought the truck it had some sort of rigged up starter button, so i already have no reference for the factory connections so thats an issue also. anyways today i went to start it and when i put the truck on acc it has power like radio etc but when i put it in run like usual to press the button and start it everything shuts off, also my tach jumps below 0 rpms while doing that? its never done that, its an aftermarket tach btw. and if i push the button it doesnt try to crank the engine or anything, also the same time this happened now when i turn the light switch on a relay by my feet in the drivers side kick panel buzzes and no lights come on. im lost here...

 

Check that battery connections are OK to battery and not loose or corroded.
I had a similar thing happen on my old volkswagen transporter - it was a bad cell in the battery.
Have you tried jumpstarting with battery cables?

 

If you have a voltmeter measure voltage directy at the battery posts and get someone to try to start it - if the voltage drops dramaticaly low - then its your battery - if no change in voltage, then measure further down the battery cables - EG between chassis and starter solenoid (large terminal on to of starter) this will help you locate the open circuit.

 

if it was just an open circuit why would my accesorie position seem to work untill i turn anything on then it shuts off, and then when i go into run or start position no power to anything but the battery has power, im going to try to jump it later when my friend gets off work so i can push it into my driveway right now i didnt get to park it in there to work on it and cant push it by myself. i dont have a voltmeter just a test light. no money fo ranything additional untill next payperiod wich is a week away :/ it was so random, i started it earlier, changed fuel filter, wich didnt involve touching any wires, it started fine, started it to test drive it after install of fuel filter was fine well for how rigged it is usually, and then go thome went to get in to start it a few minutes later to move it and it was doing this. did i mention that when i tried my lights i turn th eswitch on and a relay that is round with three prongs ans metallic colored from below drivers side dash started to buzz when switch is on and no lights came on. thanks for your help so far guys. I appreciate it!!

 

oh and also when trying to start it with the push button start and key in run position as usual it doesnt even make the famous click sound like when your battery is dead it just makes the tach go below 0 and nothing else happens :/

 

Refer to a wiring diagram to see where push button is spliced into and try if possible to put it back to oem.