I looked it up, it has the same distributor and coil as the 502 mag mpi, you could of put your red/white wire connection at the coil....anyway a volt meter is your friend,

going to confirm that tonight

if i was to go to the coil im guessing it would be this red wire?

should be, did you check the connector where the 3 fuses are located, under a grey cap I think ?

honestly didnt even know that existed. i will check

Update
have good fuel pressure. Pump dosent hold pressure after it primes tho. Weldon 1100a. This normal? Was told they dont use a check ball

Have spark. Injectors are firing Confirmed timing is good. Red/white Holley wire has 12v well cranking. Put in a new ignition module. Still no change. Will crank perfect and when you release the key it will stumble and bark a little out the exhaust. Wtf Help

I remember reading something in the holley manual when I was looking at a holley setup about using the "stock" dist. Are you sure you have the dist. and efi tied together properly...I seem to remember another harness being needed?? Sounds to me that spark is your issue in that you are losing it while cranking and when you release the key you get a split second of fire....that's my guess lol btw could you PM me some info on what holley setup you used? Is it dual throttle body? been looking at options for efi on a roots style blower...thanks and good luck!! I believe the ignition has to be separated from the boat and ran strictly off of the efi I think. I would start there....can't help on the fuel pump losing pressure...does it pump right back up when you start cranking? if not that could be your issue as well.

Oops just reread that you have spark haha...any chance you are losing it while cranking or did you check it while cranking?

yellow/red from ign key is prob wired direct to starter by someone instead of the Mercruiser remote starter solenoid. Have seen this almost a dozen times. What gives this away is the engine firing or slightly firing right after key is let go from start position.

This happens because of the long run from key ignition switch...voltage reduced enough during cranking that it won't start,,,but release starter and voltage now is enough. This is why Mercruiser uses the remote starter solenoid.

You might be 180* out on timing, make sure you're on the compression stroke #1

where would I see this? Should this be right by the starter?

Checked and confirmed the timing is right One is at one on TDC give it take a degree

Have the jumper harness for the distributor. This motor was running one the dyno less then a month ago Only some wiring and the fuel system is different Confirmed spark well cranking Confirmed injector pulse and fuel pressure well cranking. Made sure sensor readings in the Holley are good. Sees rpm No weird ass AFR or ECT readings.