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- 1994
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I think you are right, Mustang didn't, I think Rangers didn't until 88/89, my bad.
4.0l computer did, and the '87 dash will have a hook up for CEL or MIL(malfunction indicator light) just blacked out and no bulb, but I think wire should be there.
The bulb gets 12volts with key on, the other connection for the bulb is pin 17 on computer, computer Grounds the bulb(pin 17) to turn it on, OBD1(STO) test port wire is spliced to this wire.
The reason you would get 12volts at OBD1 port is because BULB is passing on its 12volts, so no bulb no 12volts at that port.
Which is why you hook up test light to battery "+" and then to Self test output(STO) on OBD1 connector, STO is a Ground
STI(self test input) Pin 48, should have jumper added to get 0volts, normally it will have 12volts
Good look here: http://www.therangerstation.com/tech_library/OBD_I.shtml
4.0l computer did, and the '87 dash will have a hook up for CEL or MIL(malfunction indicator light) just blacked out and no bulb, but I think wire should be there.
The bulb gets 12volts with key on, the other connection for the bulb is pin 17 on computer, computer Grounds the bulb(pin 17) to turn it on, OBD1(STO) test port wire is spliced to this wire.
The reason you would get 12volts at OBD1 port is because BULB is passing on its 12volts, so no bulb no 12volts at that port.
Which is why you hook up test light to battery "+" and then to Self test output(STO) on OBD1 connector, STO is a Ground
STI(self test input) Pin 48, should have jumper added to get 0volts, normally it will have 12volts
Good look here: http://www.therangerstation.com/tech_library/OBD_I.shtml