How do I disconnect the factory tach?

[Crazy D]

I've tried hooking my VDO signal wire to the green wire under the hood, and to the ecm wire, and I wanted to try every last avenue before I pull it and put in an a/f gauge. I heard that it's possible I have to disconnect the factory tach before it'll work. How do I do this?

 

[Crazy D]

No, really....

 

[U1ARUNIT]

Shouldn't have to disconnect the factory one in order for an aftermarket one to work. I had an Autometer tach and it worked fine but now I use a shift light on that wire and all is okie dokie.