I went to Autometer's website and found this:

Tachometer Signal Wire Installation
for 2.3L engine(s)
Tachometer service connector, left side of engine near DIS module, black/yellow wire. Or tap onto the black wire with yellow stripe from pin #4 of the computer, or pin #12 of the ignition module.

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'91 Ranger Ext Cab
Daily Driver/Project
2.3L 5-Speed 2WD
2" Suspension Lift