That is the basic idea... except it is not that he is getting nothing at x27... it is that when he brings 12v from the battery to x27, he is by-passing the NSS, K38 relay , and ign sw....
That is the reason we use X27 for the test point..that eliminates all cabin controls upsteam , as you can see on the schematic. So, the problem has to be downsteam from X27.
If he were getting nothing as you suggest [ meaning no power at X27] than the problem would be upstream..NSS/K38/Ign sw/fuse5.
So, X27 is a convienient test point in this circuit to isolate the problem up or down from that point..we use it b/c of it's simple convienience...it can also be used if one gets caught with his pants down somewhere with a bad NSS/K38 circuit..by jumping to that x27, it will get you home w/o a tow truck.
I have seen guys that had a bad NSS and used that jumper for a year to start their car every time the NSS failed. .....
