Might be similar to the engine computer diagnostics port, where in the laster models there were multiple test connections and you used TE1 and E1 to jump the ECU to read the codes, while in the early models, there were only 2 pins in the plug and they were called T and E1:
- http://www.4crawler.com/4x4/CheapTricks/index.shtml#TimingCheckConnector

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