4.0 swap issues

[RonD]

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

 

[moosemeadows]

RonD So if I understand correctly when I clip a test light to positive battery and put probe into STO the test light should light up whether truck is running or not, correct? What color wire would I be looking for from the dash that would then hook into the STO wire? Thanks again for the insight.

 

[RonD]

Assuming engine wiring was swapped to 4.0l then have a look at this: http://www.therangerstation.com/tech_library/EDiagrams/files/Diagram_Enginecontrols4_0_3_0_1of3.JPG

Lower right, VIP test connector = OBD1 connector in modern english, lol.

Key must be on, but engine can be off, you also need to install that jumper wire so computer will output the codes