HEI on a 78 c10 not firing.

[txchainsawgogi]

i've got 12V at the BAT terminal with the key on, and only 8/9 volts when cranking. my plugs arent firing, and neither is my spark checking tool.

i replaced my distributor and it still didnt help.

what could be causing the voltage drop?

its a 78 350.

[bd]

Make sure you have good chassis and engine grounds. 

What's the voltage at the battery while cranking?

To quickly isolate the problem to the wiring or distributor, run a temporary 10-12 gauge jumper from battery positive directly to the distributor 'BAT' terminal to see if it starts and runs.  ...Remember, you'll have to disconnect the jumper wire to kill the engine. 

If it runs, check the fusible links at the starter and firewall junction block, then measure voltage loss at and through the ignition switch and bulkhead connector while cranking.  Inspect harness and terminal connectors for heat damage.

If there's still no spark, did you replace the 'complete' distributor with cap, rotor and coil?  Is the rotor turning?

[txchainsawgogi]

i did replace the complete distributor, at TDC… made sure the rotor spins. i'll have to check the voltage at the battery, though autozone said it was good.

checked two ignition modules and three THREE! different coils. no spark.

[bd]

A broken truck can be frustrating....  So, jumper battery to the distributor and see what happens.  Perform all the checks previously posted and keep us informed.