Tack wire kills engine does that mean the tach is bad.

[Dave27]

Hooked my Tik Tock tach up today on my 68 charger 440 big block and the engine wont start with the grey wire hooked to the negative side of the coil. If I unhook it it starts right up. I know the wires are hooked up correctly and there are no shorts in the wire.If the engine is running though and I touch that grey wire to the neg side of the coil it kills the engine instantly. Thankyou in advance.....Dave

[A383Wing]

it means that the grey wire is shorted to ground somewhere after the coil...either in the tach itself or somewhere in-between

[471_Magnum]

Tach wire is probably pinched to ground somewhere.

[Ghoste]

Is the tach a reproduction one or an old original?

[Dave27]

I made and routed the tach wire myself so I know it is good so it must be shorted somewhere in the tach as you guys suggested. The rubber and micarta pads around the studs are good I did check that. Yes this is an old original tach. I did read somewhere when a tach goes bad as a safety measure it wil not allow the engine to start but that wasn't on a tach for a charger. Being an old original is there a common thing on the tach I can check that would short it out.Thankyou in advance ....Dave....The dash harness is a brand new repo but like I said I made the tach wires myself.....Thankyou......Dave

[69wannabe]

Sounds like the tach is grounded on the inside!! It most likely will need rebuilt since I don't think they were very good tach's even when they were new from what some poeple have told me. I purchased an original tic toc tach last year and didn't even try to hook it up. I sent it on to redline gaugeworks and let them rebuild it since I had no idea of its internal condition besides that it actually still looked really good on the outside. They rebuilt it completely and I hooked it up and it works great and looks great!! Money well spent 

[grizparker]

Somewhat older post, but I'm having this same issue.  Just had whole cluster rebuilt by Performance Car Graphics in FL.  Still having this issue.  Any way to test if it is grounding in tach or somewhere else?  Just because it was rebuilt doesn't mean that the tach hasn't been accidentally messed up during installation , but I'm giving them the benefit of the doubt first...
Anything else I can try?

By the way, my '69 charger RT has had had electronic ignition installed on it over the years.   The new wiring has to consider that.  Didn't know if that created any special situations to consider...

[471_Magnum]

Any way to test if it is grounding in tach or somewhere else? 

Disconnect the tach wire at the tach and the coil. Then check for continuity to ground.