Obtain And Wire The Tachometer Signal
(Click any pic for an enlarged view)

This was one of the few jobs that made me paranoid. Hacking into the Powertrain Control Management ECM wire harness is bad enough, finding and splicing into 1 of 56 wires and getting it right just made me paranoid. Well before I dug into the task at hand, I obtained detailed information on each ECM plug and pin assignment. Armed with this data I felt a little better about finding the elusive wire.

One thing that is nice is that the ECM is bolted to the side of the intake manifold. The ECM is unbolted and hung with a bungee cord to hold it up for ease of access.

The ECM has three data cables. From left to right they are X1, X2 & X3. The wire needed is located in X1. After pulling the latch and removing X1, you get the first view of the connector plug.

To locate the wire and pin assignment, I used a trick I learned from my father. Take a multi-meter and set it to continuity. Clip each end of the multi-meter to a strait pin.

Find the pin hole that represents the wire you are looking for and insert the pin into the hole.

Since there most likely will be multiple wires of the same color, you will have to poke each of the same colored wire until the meter shows continuity. If you are lucky you will hit it in the first try. I was not.

Once the wire is located, you need to splice into it. Then re-wrap the harness in electrical tape. I would wrap it tight so there is no movement inside the harness.

Here ECM cable X1 is reconnected and ready for replacement of it's protective wire loom.

With the wire tap complete, it is time to connect the tapped wire to the main wiring harness. Here I am using a single wire connector salvaged from a Cavalier.

After the connection is made, wire loom is added.

The ends of the wire loom get a couple wraps of electrical tape to keep the wire from coming out.

One can only hope there is no lingering damage caused by the free style hacking of the ECM data cable. Only time will tell.