Chrysler Repair: Tachometer Hookup on 3.3L Engine, spark coils, roland roland

Question
Roland,

I have a diagnostic Tachometer that I would like to hook up to my 1990 New Yorker with a 3.3L engine. Where would I make the connection that used to go to the (-) terminal of the ignition coil in the old days?

Thanks for your consideration.

Dennis

Answer
Hi Dennis,
You will find a pulsing 12V volt signal that is proportional to the rpm on any one of three wires at a 10-pin gray colored connector behind the battery. The wires are the ones that supply each of the three spark coils primary winding. Their colors are: dark blue/gray, dark blue/black, and black/gray and they are side-by-side on the connector. So you could probe any one of those three wires which pulse once each engine rotation. I suspect that the rpm reading will have to be multiplied by a number that depends upon the dial setting of your tachometer (3,4,6,or 8 cyl). The 4 cyl setting is based upon 2 pulses per engine rotation at the spark coil so the rpm maybe 50% too low on the meter reading, but you get the idea. So find that gray connector, find the wires and probe one of them with your tachometer lead with the other lead grounded and you should have a tachometer reading, I suspect.
Roland
Roland