Self-Proving Vehicle Grounding Verication System
Servicing the ST-47
Page 13.
5.4 Test Procedure 1 - Wire-Through Applications Only
Problem: The overll prevention plug is connected to the tanker mounted overll prevention system
and the RED non-permit lamp stays on. Unit does not “permit” externally connected devices.
Procedure 1, Step A
Does the tanker have a Scully Ground Bolt installed and wired to Pin 9 of the overll prevention
Socket?
Procedure 1, Step B
If you have a Scully Rack Tester, plug the overll prevention cable into the socket on the tester. If
you do not have a tester but do have a Scully Ground Bolt, use jumper wires to connect the green
wire on the bolt to Pin 9 of the plug and connect the body of the bolt to Pin 10
.
Does the ST-47 Permit?
Procedure 1, Step C
Using a Multi-Meter set on DC volts measure the voltage between Pin 9 (+) and Pin 10 (-) of the
overll prevention plug.
Is the voltage between 24 and 30 volts DC?
TIP
Overll Plug Pin Identication- Orient plug with pins facing you and the
molded-in arrow positioned at 12 o’clock, Pin 1 is located where the
arrow points. Count pins from Pin 1 in a clockwise direction. Pin 9 is in
the center on the left. Pin 10 is in the center on the right
NOYES
Go to the next step Install Ground Bolt on tanker (Scully Part# 08560)
NOYES
Trailer grounding system is at fault. Have
tanker owner check the installation or,
contact the Scully Service Department for
assistance.
Go to the next step
NOYES
Go to the next step
Using an open end socket wrench, open the plug
and cable junction box. Remove line power to the
ST-47. Remove wires that come from the cable
and are connected to terminals 9 and 10. Power
the ST-47. Check the voltage at terminals 9 (+)
and 10 (-) on the terminal block found inside. If
you now read 24 and 30 VDC at terminals 9 and
10, there is a problem in the cable or wiring to the
ground ball plug. Correct the problem. If you still
get no voltage reading, go to the next step.
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