90 T-bird tach install

Recently tachometers were on sale at princess auto for $10 so needles to say i bought one. I had no problems hooking the tach up to a ground, 12V+, and hooking it into the lighting system. I can not for the life of me find the wire to splice into for the tach signal!. please someone help me out and tell me where the tach signal wire is on my car.

1990 thunderbird LX 3.8L

Your best bet would be to contact the tach manufacturer and ask them. I have a 95 and 97 that the tach signal comes from the PCM.

negative side of the ignition coil connector