Engine won't fire when tach wire hooked to coil

[cataclysm80]

Thanks Cody.  Any suggestions regarding the missing cardboard washer.  I assume a rubber washer would work to insulate the connection.  Your thoughts.

I like replacing the old cardboard/paper washers with plastic washers.  I think they're nylon.  I think it's more durable that way.
I don't like using rubber washers because they're so squishy.

[usraptor]

Finally, after 6 months I got the Cuda Tachometer working with the factory wiring.  Stumbled on the problem by accident and still don't know why it made a difference.  The "factory" connection on the back of the tach wire that goes to the coil is a bayonet connection.  There is a male connector on the back of the tach that is held on with the nut and the female connection on the tach wire slides onto that.  In desperation I ran a wire directly from the coil to the back of the tach to bypass the factory wiring.   I took the male bayonet connection off the back of the tach and just used a regular round crimp connection, tightened it down with the nut and the engine fired and the tach worked fine; So even though all my tests showed no shorts in the factory wiring after I had made numerous attempts during the past six months at finding a short, without success, I just gave up and decided to make this direct connection between the coil and tach permanent.   I had to cut both ends off the test wire to thread it through a small hole I drilled in the plastic bulkhead and just decided to put a bayonet connection on the end of the wire that connected to the back of the tach and  connect it to the factory male bayonet connection. When I did this the engine wouldn't start again!?@#$^*%#!!^%*&*.  I disconnected the wire at the coil and the engine fired right up!.  So thinking that the only thing different was the male and female bayonet connection on the back of the tach, I took the male connection off the tach, cut off the female connection from the factory wire and replaced it with a round connection like I had done during the initial test from coil directly to tach.   I reconnected the factory tach wire to the coil and the engine fired right up and my tach works!?  Have no ideal why the bayonet connection on the back of the tach caused it to short out the coil since it was the factory connection, but don't care now as my tach works with the factory wiring and I no longer have to spend hours twisted up under my dash trying to figure it out! 

[RUNCHARGER]

Good news you got it working again. It's fun under there isn't it?

[CamasCuda]

thanks for the heads up and persistence.   I am struggling with the tach too.   although the car runs.  I ran a jumper yesterday to check the wire running from coil to back of tach, it was OK.   I used one of those "electrical audible tools", the sound was not as loud as it was when checking directly across the battery.   i' will try a total replacement line tonight, bypassing the bayonet connection on the back of the tach.    the other wire coming off the back of the tach, I pretty sure Dark blue, seems to head off to a connection with the power feed to radio/8track player.   Wondering if you know, is the "other dark blue wire" a power feed supply?  ... if the tach still doesn't work, after trying the by-pass jumper, the blue wire was my next investigation.

[usraptor]

When you say "Other blue wire" are referring to the dark blue wire connected to the back of the tach or another blue wire, cause I'm not seeing another blue wire connected to the tach in your picture?  The Blue wire connected to the back of the tach with the 90 degree rubber boot is the power wire.  The Grey wire with the red tracer goes to the negative side of the tach.  When I checked my wire and connections with an OHM meter everything checked okay also, even with the bayonet connection in place.  It wasn't until I ran a replacement wire from the coil to the tach with just a typical round connection that I got the tach to work and eventually discovered that there was something wrong with the bayonet connection that was grounding out the coil for some unknown reason.  Good luck and let me know what you find out.

[CamasCuda]

Thanks for the comments.  Yes, I should have said the other wire, which is blue.   If you know, is it just straight 12+ power or some reduction in voltage?  I was thinking of running a jumper for both and testing results, BEFORE I go out and buy a new tach.

[Chryco Psycho]

Blue wire should be 12v , it is not fed from the voltage reg