Make a small cut about 1/2″ long and remove the insulation on the automotive wire. Then you will need to count the individual strands of copper. Next use a micrometer and measure one of the strands. Also count the total number of strands that are present in the automotive wire. Look at the following information to determine the gauge of your automotive wire.

7/.028 = 20 (7 strands that measure .028 each equals 20 gauge)

16/.030=18

19/.029=16

19/.027=14

19/.025=12

19/.023=10

19/.021=8

37/.021=6

There are four distinct types of insultation on automotive wire and cable:

1. GPT
2. GXL
3. SXL
4. TXL

GPT is the only automotive primary wire insulation out of the four that is extruded insulation. Extruded insulation is rated -40 C to 80 C. It is created by heating PVC and then extruding it through a die on the stranding. This insulation can be melted with a heat source, changing the form.

The other three automotive wire types, GXL, SXL, and TXL are all crossed-linked insulation. Cross-linked insulation is rated -51 C to 125 C. It is created by extruding PVC through a tube, under heat and pressure, in order to ‘cross-link’ or change the molecules of the insulation to another state.