1999 buick regal will not start,check battery starter,fuse,replace both crank & main relay,but still will not start.

I would check your starter switch relay. It's the relay responsible for sending full battery cranking amps to your starter.

Check for loose corroded or bad battery ground cable. Check starter relay.

Start by checking the fuses and then the battery connections, this sounds like a fuse poped maybe a main fuse, if its a fuse then replace the fuse if it pops again then theres a dead short somewhere, these are famous for bad starters and starter relays going bad, so see when fuse pops again if its when key is turned on or when you try to crank the motor, if its when cranking then its mostlikely the relay or starter, this main fuses would be in the engine compartment fuses box.

On the passengers side close to the battery there is a junction box.There are fuses and relays in here.Remove the cover and check the crank fuse.It is a maxi fuse so it is one of the big ones.If you look under the cover it self it will show which fuses are for what circuits.If this fuse is blown then replace it with the same size fuse.If it is good then you will have to check and see if you are getting power to the starter.This will be at the purple wire on the starter.You need to have above 9 volts for the starter to turn over.The best way to check this is with a multimeter.If you have over 9 volts then try tapping on the starter while attempting to start the vehicle.If it turns over then replace the starter if not you will have to find out if you are getting power out of the park/nuetral switch.This is located on top of the transmission by the shift cable.Power comes in on the yellow wire and goes to the starter on the purple wire.If you have power going in but not out then replace the park/nuetral switch.Hope this helps and let me know what you find.Good luck.

If it has spark at the plugs, then it may be the fuel pump relay, or a fuse going to it, the relays are in a box under the hood they should be marked, check them w/ a test light.

Pass key is the security system which disables the car if it is stolen. You need the remote or a key with a chip to start the car. go to a dealer, prove ownership with registration and they will be able to help you out

check your ignition switch contacts...might also be an electrical bad connection somewhere. Also check the fuses. Check also the voltage going the solenoid or test the solenoid too.

change the starter relay located in the fuse box in the engine compartment near the battery.

check your nuetral safety switch