Crank no start

Couple questions. When you swapped the engine, has this engine ever started since you installed it?

If not, then we need to check for spark and fuel to find out what we don't have.

You need spark, fuel, compression, and air in order to start the engine.

https://youtu.be/dCjmRL3p4Cs

So, I suspect we have an issue with the ignition system so I would suggest pulling a spark plug and find out if we have spark and go from there.

This black and white wire is a ground wire and if you have 6 volts on it then that sounds like it is not a good ground connection.

https://www.2carpros.com/articles/how-to-check-wiring

So, let's find out what this ground goes to and if it is the PCM then that is where we need to start.

Okay. If you are getting sparking when you are touch a ground wire to a ground location that means you still have voltage on the circuit. This is due to a short in the component that is on the circuit, or the ground location is not good enough.

Basically, the way a circuit works is you have your source of the voltage (the battery) and the wire leads from the source to the load, which is a light bulb, control module, solenoid, or whatever needs to use the voltage. Then the ground wire leads from this load to the ground location. The voltage is what causes the component to operate and 100% of it must be used in the circuit either by the load or wiring.

So, if you have 12 volts coming from the battery and you have a single component on the circuit that uses voltage then this is going to take the voltage up and all that will be left is what the wire requires to return to ground. So, if you have 6 volts on the ground then you have something on the circuit that is requiring voltage in order to get back to ground. Normally this is due to a poor ground connection, or the ground is just not a good location.

What I would do is use another wire and just jump it back to the negative battery cable and this way you know you have a good ground for testing purposes. If all the issues go away, then you know the ground location was no good.

If not, then you have another issue.

What is this ground wire for? What component is it grounding?

Okay. If this is for the PCM then that will explain a lot. This would make it G103 or G104. Take a look at this picture and see if that helps.

These do not go in the same place but that doesn't matter as long as it is a good ground location. What I would do is pick a location that you want to use and then measure the resistance between that and the ground post of the battery. If the main ground cable is connected to the battery and the engine, then the entire engine block becomes a good ground location as it is all highly conductive metal. So, you should have little to no resistance when checking the resistance through the ground side.

If you do then that is not a good ground, and you should either figure out why or pick another one.

What I would do if you are struggling to find a good ground is just route the wire back to the negative battery post. No matter what, all ground locations are trying to get back to the negative battery post as this is the final destination for all electrical circuits. Electrical circuits must be a complete circle in order to operate and the fact that they all start from the battery means they must end at the battery. The fact that the frame and drivetrain are metal is just a way that they can keep from routing wires all around the vehicle and back to the battery.