Can't get a Tach to read correct.

[AmadeusCharger500]

Car was fine till I got it back from paint. The guy had it for 2 months and had some trouble starting it. Not sure all whatass he did but one of the things is My tach didn't work anymore.
I unhooked it and pulled it out to check all the connections. Retry and still no reading. So i went and bought a new one. This one is tell me the car is idling at 2500rpm. Which it clearly is not or it would be crazy to drive.
Car is 74 charger using msd Ignition box.

Thanks,

Heath

[Ghoste]

Do you have a tach adapter for the MSD?

[lisiecki1]

factory tach or aftermarket?

[AmadeusCharger500]

Aftermarket tach, Sunpro or something. It worked fine before goin caput at the paint guy. in fact I have the same tach in another car has worked for years with the msd. And I've not used any sort of adaptor. It's hooked to the negative side of the coil.

[firefighter3931]

Heath, there is a spade connector on the MSD box labelled tach output and that is where you're supposed to connect the signal wire (from the tach) to. Most tachs will read incorrectly if you hook up to the negative side of the coil due to the multiple spark discharge below 3000 rpm. 

I'm wondering if your ground was compromised when the car was painted rendering the old tach non operational ? 



Ron

[lisiecki1]

also, if you open up quite a few different aftermarket tachs they have dip switches inside them that need to be set according to the number of cylinders in the application.  If you can give me a model number or a picture of it I'll try to locate the owners information online and figure out how yours should be set.  My dad has had a sunpro on the GTX for 20 years with no problems and i used to run one in the charger 

[AmadeusCharger500]

Seems it was a combo of both things. I reattached direct to the ignition box and I flicked a small switch in the back before it read correct. All is well again thank you!