I have finished this swap like 5 or 6 months ago and now all of a sudden voltage drops when the car is running it goes all the way down to 8 volts and then dies. I just went out today and got a new alternator and replaced that and the problem is still there. I put all new plugs, wires, distributor when I did the swap. my speedometer doesn't read anything either. I bottomed out on a speedbump 2 days ago and this problem has been since then I didn't see anything that got cut or knocked off or anything. I was getting codes for heated o2 sensor but I reset the ecu and no check engine light now and I still have the problem.
the only thing I can think of is a short that occurs only when the car is running. is there a sensor that when it goes bad can cause this or something? any suggestion please respond thanks

 

So when you start the car and its idling, the voltage at the battery is 8v constant?

What if you put jumpers on it from a different car/battery - the voltage should then read ~14v... does the car still die?

 

Check voltage to the battery when the car is running with a volt meter.. voltage should be in the 13-14 volt range...

Check engine ground straps and the battery negative cable as well, i.e. your battery could be bolted to the bulkhead or fenderwell, but the motor is having trouble sending the negative signal cause the bulkhead is not bolted to the motor via a groundstrap.. alternator grounds via the motor

You have to verify positive+ and negative- signals are getting to the battery..

 

the voltage drops as the car is running I just put in a new alternator and the same problem occurs. I measure the output on the alternator when the car is running and I get like 8.5 volts and dropping. I am going to check continuity between the wires on the plug on the alternator and the ecu next.

 

my dumbass I figured it out. Lets just say learned a lesson. Start with the most obvious first. after a new alternator $145 later and a waste of a few hours putting it in it all ended up being the alternator/speed control fuse under the dash. should have checked that first huh?