I just bought a Midtronics PSC-550S for whenever I need to do any diagnostics work in the future. Quick question, does it need to be connected directly to the positive post of the battery and a chassis ground, or can it be connected to the battery posts in the engine bay?

All the official Jaguar docs I can find with searches just vaguely say to connect it to the car.

 

Don't know but I go straight to the source. In the trunk + on positive terminal of battery. - to where the ground strap is attached to the body of the car.
Mainly because I have measured the car using 30+ amps for hours on end when using SDD. Why so much current drain? I don't know but on my car I see large current draws.
I just assumed it's an SDD requirement?
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Lotusespritse, due to the power supply being capable of up to 55 amps, I would be hard wiring it to the battery and a ground point in the trunk. That is more current than 99% of the wiring in the car can handle. So, instead of taking a chance and hooking to a circuit that could handle the power, guarantee yourself that it will handle the power. This may even be something worth considering a welder type of plug for to allow you to unplug the device when you are not using it and have a connector that is capable of handling the current. Yes, a plug like what I am talking about is an added cost, but it will make life a lot easier and will guarantee you won't have issues in the future.

 

Good points. I will hook it up in the trunk.