measurement of pressure transmission?

I have backhoe loader JCB 3CX from 1990 year, with transmission:

Manufacturer -JCB
Type -Syncroshuttle
Gear selection -Manual
Shuttle control F/R -Power shuttle

Transmission pressure switch does not close contact /bright lights/, I measured the pressure with the gauge in place of switch and got a pressure value of 5 bar. Please send me a measurement scheme for transmission with the values of pressure in order to examine the transmission.

Thanks in advance