JLG 1250AJP Troubleshooting Manual page 243

Service - Voltage Reading
DO NOT PIERCE WIRE INSULATION TO TAKE VOLTAGE READINGS.
It has been common practice in electrical troubleshooting to probe wires by piercing the insulation with a sharp point. This
practice should be discouraged when dealing with the AMPSEAL plug assembly, or any other sealed connector system. The
resulting pinholes in the insulation will allow moisture to invade the system by traveling along the wire strands. This nullifies
the effectiveness of the connector seals and could result in system failure.
3128411
CAUTION
Figure 2-23. Connector Installation
SECTION 2 - ELECTRICAL REFERENCE
1250AJP 2-243