what do you mean by 12v out of coil?
do you mean the distributor cap wire marked BAT has a reading of 12 volts?
do you hear the fuel pump engage for a few seconds when you turn the key to run?
here is a set of diagnostics for an HEI distributor
1. With the ignition on, connect a voltmeter (or test light) to the + post or HEI BAT terminal located on the distributor cap.
+12 volts or Test LIGHT ON: Go to step 3.
No voltage or Test LIGHT OFF: Go to step 2.
2. Check for continuity or voltage drop in the ignition switch and in the circuit from the switch to HEI BAT terminal. Fix missing +12 volt problem.
STARTS: Stop—you’ve found the problem.
NO START: Go to step 3.
3. Remove a spark plug wire and insert a HEI spark tester ($2.99 from Harbor Freight) in line. Crank the engine and observe the light in the tester.
3a. Alternatively remove a spark plug wire and insert a metallic extension in the end of the wire. Using insulated pliers, hold the spark plug wire no more than .25 inch away from the engine block while cranking the engine. If you use the alternate method be very careful to hold the wire no more than .25 inch away from the engine. Greater distances can cause damage to the ignition module.
LIGHT FLASH IN TESTER or SPARK JUMP TO ENGINE BLOCK: The problem is not the ignition system. Check the fuel system, spark plugs, timing, and internal engine condition.
No light or NO SPARK: Go to step 4.
4. Remove and inspect the distributor cap for cracks and carbon-tracking. Visually inspect the distributor mechanism for moisture, corrosion, or burns. Repair as needed.
STARTS: Stop—you’ve fixed it.
NO START: Go to step 5.
5. Set an ohmmeter to the low scale. Connect the leads across the HEI’s “BAT” and “TACH” terminals.
ABOVE 1 OHM: Replace coil. If vehicle still doesn’t start, go to step 6.
0-1 OHM: Go to step 6.
6. Connect one ohmmeter lead to the “BAT” terminal and the other lead to the coil contact in the inside-center of the cap. Switch the first lead to the “TACH” terminal and recheck.
EITHER TEST READS 6K to 30K: Coil is OK. Go to Step 11.
BOTH TESTS READ INFINITY: Replace the coil. If the engine still won’t start, go to step 7.
7. Remove the green and white leads from the HEI control module. Connect the ohmmeter from ground to either lead.
INFINITE reading: Go to step 8.
LESS THAN INFINITY: Replace the pickup coil. If the engine still won’t start, replace the module.
8. Connect the ohmmeter across the green and white pick up coil leads.
READS 500-1,500 OHMS: Repeat Steps 7 and 8 while moving the vacuum advance with a screwdriver. If reading is still OK, replace the module.
DOES NOT READ 500-1,500 OHMS: Replace pickup coil. If the engine still doesn’t start, replace the module.
That is it. You will notice that there is really no diagnosis of the module. When everything else reads correct the module is replaced by default.