Without knowing "your wiring."...........................
Where is the battery? front? trunk? Is the main battery ground to the block?
Are you sure the battery is OK? Is it charged up?
Cable connections?
Get things immediately down to the absolute most simple terms...............
The engine, the battery and the starter
Main cables should be hooked to the block and the starter, or to the relay stud and then a big at least no4 jumper down to the starter.
Jumper the starter with a clip lead/ start switch/ screwdriver.
When you do this, make some tests
1--Take your meter and hook one lead to the block.
STAB one lead into the battery positive post, jumper the starter. Meter should read more than 10V, the higher the better when starter is jumpered
2--If OK, move the meter lead to the battery cable clamp, repeat
3--If (2) is above 10V, move the meter lead to the starter stud. Repeat.
Somewhere in these 3 you should get a low voltage reading.
CHECK THE GROUND:
1--Clip one meter lead to the block, set meter for low DC volts, and stab positive lead into the top of the NEGATIVE battery post, jumper starter.
You are hoping for a very low reading, the lower the better. More than .3V (3 tenths of one volt) means you have a problem.
If the reading above is more than 3 tenths, repeat with meter probe stabbed into the NEG battery clamp. If this is low, and (1) above was high, you have a bad connection right there in the clamp to battery post.
If this reading is still high, you have a bad ground connection