they are present in autodata

This is what i could get out out of tis 2000
B-001 DIAGNOSTIC TROUBLE CODE
P1590 Engine Running Signal Low Input
Short to ground or interruption in circuit to control unit terminal 39
Concerned Terminals:
1, 2, 39
Work Order Description
Ignition OFF
Disconnect wiring harness connector from:
Diagnostic tester
Ignition ON
Engine running at idle speed, operating temperature
Increase engine speed to 3000 rpm
Measure voltage between the following terminals:
Battery Voltage (Positive Terminal)
&
Ground
nominal value 13.5 ... 14.5 V
if above are not true then : Defective component: G2 Alternator ; if they are true then
Work Order Description
Ignition OFF
Disconnect wiring harness connector from:
K70 Control Unit - Diesel
(Wiring Harness Connector 81P )
Ignition ON
Connect test lamp ( 55 W ) and multimeter in parallel and measure voltage between the following terminals:
K70 Control Unit - Diesel
Wiring harness connector (wiring harness side) terminal 39 (81P)
&
Ground
Nominal Value greater than 11 V
if above are not true then:
High transition resistance between:
S1 Switch - Starter
Wiring harness connector (wiring harness side) terminal 15
&
K70 Control Unit - Diesel
Wiring harness connector (wiring harness side) terminal 39 (81P)
and if true
Work Order Description Nominal Value
Connect test lamp ( 55 W ) and multimeter in parallel and measure voltage between the following terminals:
K70 Control Unit - Diesel
Wiring harness connector (wiring harness side) terminal 1 (81P), 2 (81P)
&
Battery Voltage (Positive Terminal)
nominal value: greater than 11 V
if these are not true either then :
High transition resistance between:
G1 Battery
Wiring harness connector (wiring harness side) terminal 31
&
K70 Control Unit - Diesel
Wiring harness connector (wiring harness side) terminal 1 (81P), 2 (81P)
but if true
Defective component:
K70 Control Unit - Diesel
if someone knows the wiring and what joints i should check please post some pics here so that i can see where to check because my hunch is that is a non-perfect contact somewhere but i don't know what g2 k70 etc are