OBD1 is different, I don't think there is 12v at the test port.
This is a page that shows how to read OBD1 codes with a meter or test light: Ford Ranger - Testing EEC-IV Equipped Engines
If there was 12v at the test port then meter or test light would use that instead of battery.
I am just guessing based on that web page
Does the check engine light(CEL) come on when key is turned on and then go off, if not there could be a power issue with the computer