Tachometer

[Caparco]

Got my restored/recalibrated tach back from gauge specialists,
I'm sure they did a great job, but couldn't wire it up for some reason, the grey/ blk tracer wire gets lost in the bulkhead and I have a brown wire leading to the negative side of coil,
To test it I wired it straight from the tack to the negative side of the coil, does it matter that it's a MSD ignition coil?

And the blue wire why would it go to the turn signal flasher of all places? Does this feed out to the turn signal switch?  Does this stop it from working if I'm having all sorts of turn signal switch problems?

[Bullitt-]

Diagram I have shows the blue power wire for the tach branches off the plug for the radio

  Could you have the radio plug on the flasher perhaps? 

[Caparco]

Not sure where you got that diagram?

[Jay Bee]

Could it be possible that 1970 & 1972 are different.    The OP's profile says 1972 Challenger.

[Bullitt-]

Could it be possible that 1970 & 1972 are different.    The OP's profile says 1972 Challenger.

Yes, the only Ralley dash schematic I have is for a '70. Ultimately it should make no difference as long as the blue wire gets constant voltage when ignition is switched to run.

More confusion may be the location of the GREY wire that runs to the negative side of the coil. Every diagram I find shows it runs trough the bulkhead in location 20 yet I've seen it discussed & I confirmed looking at my '73 that at least in some cases it runs through a separate grommet to the brake booster side of the bulkhead.
 
Coil brand should not cause an issue used on an otherwise stock ignition but many aftermarket systems don't work with the factory tach. I have read that the modernized replacement internals should.   

[Caparco]

Got it working!

Thanks for all the help guys exactly what I assumed it was the blue power wire was not getting power , bypassed the turn signal flasher and plugged it in direct and it works fine.

[70vert]

if it is just an MSD brand coil I don't think it matters. But if it is an MSD ignition then I believe it does require a "tach converter", sold by them. a small blue metal device I think.