1999 chevy blazer will not start. No spark!?!? No spark from the coil to ground.

Does the engine have spark to the spark plugs? Is there 12 volts to the coil and is the coil being triggered on the ground side? Check to see if the coil is sending spark to the distributor. Several more things to check that will not let the truck start. Check these and get back with me and I will help you more if needed. Good luck.

Check the plug wire from the ignition coil to the distributor cap.
If you haven't already, replace the distributor cap and rotor.
The GM Vortec's have issues with moisture getting inside the cap and rotor and causing problems.

I’m happy to help further over the phone at https://www.6ya.com/expert/jason_00b31cc8f593773a

You need to check for a loose ground again. The dash seems to have a loose ground. Your heat and ac are controlled by motors that get input from your switch. You might try following that harness and see if there is a loose ground. Other than that I don't have a clue. You might also check near the firewall and make sure the ground strap there was bolted to the engine.

year? white usually goes to tach.

change out your distributor cap and rotor button

When you go to an auto store and they give sell you spark plugs they should already be gapped to spec. There is no need to adjust the gap. This may be the reason your car will not start. I would try new spark plugs first then wires. Since the vehicle is a 99 it probably could use a tune up (spark plugs, wires, coils, cap, rotor, chassis lube, and transmission fluid check and flush if needed). Also make sure that the engine block ground strap is in good condition and that there is no corrosion covering the ends of the ground strap. The ground strap is typically located near the firewall and is directly attached from the engine block to the frame of the car.

the ignition coil changes low voltage from the battery (12 volts) to high voltage (about 50,000 volts) to fire the spark plugs and ignite the fuel in the engine cylinders and drive the piston down

CHECK BATTERY VOLTAGE FIRST IT SHOULD BE 12.5 VOLTS.IF NOT REPLACE BATTERY HAVE ALTERNATOR CHECKED.IF BATTERY GOOD.HAVE VECHICLE SCAN FOR PCM PROBLEMS - CRANKSHAFT SENSOR PROBLEMS OR CAMSHAFT SENSOR PROBLEMS.IF ALL IS GOOD GET A SPARK TESTER AND FUEL PUMP PRESSURE GAUGE TESTER.IF GETTING NO SPARK PROBLEM COULD BE LOOSE BAT.POWER SUPPLY WIRES AT IGNITION COIL MODULE OR IGNITION MODULE FAULTY.IF FUEL PUMP NOT RUNNING CHECK FUSE ABD RELAY IF BOTH IS GOOD FUEL PUMP FAULTY.

Looks like you've covered the basics, make sure the firing order is correct with your spark plug wire replacement. Hope this diagram helps.

check ignition fuse.if okay.remove one of coils connectors using a test light .turn ignition key to on position .terminal 1 on the connector to coil is the first to left with the locking tab up. then remove the ignition module connector terminal 4 is 12 volt supply.4 terminal to the right with lock tab up.connect test light to ground.take the pointed end touch both the terminals for 12 volts with ignition on position.if getting 12 volts.you have PCM PROBLEMS OR CRANK POSITION SENSOR..IF GETTING NO 12 VOLTS YOU GOT A BLOWN FUSE OR GROUNDING PROBLEMS.