There isn't a connection on a distributorless engine you can use with an older service Tachometer
On a V6 you could try using a sewing needle to pierce one of the coil packs 3 Ground wires, the RED wire is 12volt, so any of the other 3 is fine to use
On Fords waste spark system, each coil in the pack sparks 1 time per RPM
On older service Tach it would expect 3 sparks per RPM on a V6
So 300RPM on tach would be 900RPM on engine
OR.....................
If you have $15-$25 and a Smartphone, you can buy a Bluetooth OBD2 reader, like an ELM327
These connect to the OBD2 port in the cab of ANY VEHICLE sold since 1995, its the law, so not a Ford thing
And you can use a free APP on your phone to connect wirelessly to the reader, which will have RPM and a whole lot more info, LIVE, that you can watch from engine bay or............where ever around the vehicle
This is WAY WAY BETTER than just the tach signal for diagnosis
If you decide to get this also get an extension cable with/for it, I find that some vehicles have OBD2 ports that are off center from their holes so the Bluetooth units can't slide in without removing a panel, the $4-$6 extension cable allows better plug and play on those vehicles
And just a heads up
Lean code does not mean engine is running Lean
It means the computer calculations of correct Air/fuel Mix was Lean and computer had to correct it, so computer is giving the driver a heads up to check the system
If your engine is Pinging/Knocking that can mean Lean running but there would be NO code, because computer wouldn't know it was running Lean, or it would have corrected it