Wiring harness test circuit is composed of 8 circuit boards. There are 2 CPLD chips in each board, one CPLD chip was used to send test signal, and the other used to receive the test results. The CPLD interior logic circuit is shown as in figure 4. The main units is composed of a 6-64 decoder and a 64-1 multiplexer,which are realized with VHDL language and are used to select the wiring harness test address and transmit the test data. There are also data latches and logic control circuits on the CPLD. Because the apparatus realizes up to 512 points test, each CPLD need to perform 64 nodes test and data transmission. One or more circuit board was selected by the chip select signal initiated