How-to Guide: Hook 42 Pin Harness Connector on 99-04 Mustang

You should see the large, square 42 pin wire harness connector in the corner of the engine – seen in the picture, if you want to diy install a tach adapter purpose on your 99-04 Mustang.

At most, the 42 pin wire harness connector located in the corner of the engine bay where the passenger fender meets the firewall of your Mustang (other Ford car and trucks maybe different 42 pin connector location).

1. Pop the plastic cover off the top of this connector to expose where the wires enter the connector and to expose the wire pin numbers.
2. Locate pin number 34 which will be in the corner of this connector.
3. You may see the wire color can be Red, Red with a Green stripe, or a White wire with a Blue stripe.
4. Cut this wire in half so that you now have two cut halves.
5. Hook the Red wire of the adaptor to the cut half coming from the connector.
6. Hook the Red/Green of the adapter to the other cut half.
7. Ground the Black wire of the adaptor.
8. The Gray wire of the adapter will now provide you with a good tachometer signal.
9. See the above diagram – click to enlarge for How to Hook 42 Pin Harness Connector on 99-04 Mustang