I want to do a compression test on my mk10 , but the starter solenoid is not easily accessible . Does this mean I have to take all the plugs out and leave the ignition switched on ?
You are going to take all the plugs out anyway to get good revolutions and not tire out the battery, just disable the coil and proceed as best you can from there.
Hi,
Just like Robin said, plus on my ex S1 4.2L E-type I also unplugged the fuel pump.
Make sure all the throttle plates are also wide open (WOT) when you do the cranking, if you use the starter button on the dash just floor the accelerator.
On my MKV it’s easier, no ignition switch needed, just push the solenoid on the firewall. 
Cheers!
as said…disable coil and fuel pump…you don’t want fuel being pumped…and 6 loose spark plug wires doing what they do…sparking away…!! The screw in comp tester can be more reliable than the rubber push in altho those have been used by many, for years…, and with screw in you get to see the dial comfortably with a 12 inch or so hose to the dial…there should be a release pressure button…you want about 4-6 revs…as the dial moves up…stop when the dial steadys, use same method on all 6.: then…while at it…do it again…this time a teaspoon of light engine oil in the spark plug hole…give it a 3.87 seconds to flow to the cylinder wall.then test…, then the next one…(oil one cyl-one test…) and so on. This will tell you the condition of rings/to cyl wall… A mid low PSI cylinder will improve a lot if it is rings. A very low psi…that stays low…is valves. If you find issues…the next test is a leakdown, or…one cyl at a time when each is TDC compression (thus valves closed) use a section of small heater hose and just blow into the spark plug hole…: with both valves closed…it should not be easy. If it is…confirms a valve issue…next test would be more air…listen/check to find where it is escaping…intake valve? exhaust valve, or radiator --head gasket)… Nick
Thanks Nick , I do have the screw in type of comp tester , so will do !