73 Tach Differences - 3 or 4 wire?

[ChrisZ]

I still think you can use a 260/280Z tach.

Chris

[70 Cam Guy]

This is the back of my -73 3 wire tach.

Chris

Now that looks a lot like the picture I took of mine back when I first joined. My car has a 6/73 production date

[ChrisZ]

Yes you did and that picture was for me, the last time this subject was brought up.

[zKars]

I am pleased in this case to be taught something new! Who knew 3 wire tachs were available in 73! And that plug is an in-line 3 pin! Unlike the square 4 pin earlier ones, certainly nothing like the 8 pin 280 style! Nothing like that in the FSM, eh? And you wonder why you have to carefull when getting a replacement dash harness!

Now, how are they wired? Is that one terminal routed to the coil negative side with an inline 2.2k resistor like all 280 (maybe I should watch my usage of 'all' !!!) The presence or lack of the need for that resistor will make a difference when using a later tach for Dave if we can't find him an official correct 3 wire 240 tach.

Good stuff gang!

Edited December 15, 2009 by zKars

[dcaverre]

Chris,

The tach hovers just above 0 and is sometimes stone dead. Sometimes it will kick in at a high rpm, work for awhile then die down to zero. Sometimes a bump makes it work.

Dave