Tach testing 84 Carrera

[jlynch1960]

My tach started to cut out from time to time but would bounce back after a brief rest. I just figured things warmed up and a solder connection was lost inside the tach. A couple of weeks ago it died outright. Switched it out for another I had sitting around, but no go.

After reading some threads here, I tested the TDC and speed sensors at the Dme harness - all continuity and AC values were within range. (Actually perplexed as to why it's an AC test, but that's for another day).

After reinstalling the harness I noticed the tach would jump up but then die when I started the ignition. Suggesting perhaps a bad connection between the Dme and tach.

Is there any way to test the output at the actual tach harness. I read a couple of posts discussing oscilloscopes, 5v and 10v square waves etc, but they seemed to involve bench testing the actual tach and not testing the inputs at the tach harness itself.

Any thoughts on how I should proceed? I guess I could start with some contact cleaner, but I'd like to know if there's actually a way to test the signal at the harness.

Thanks.

[Elombard]

If you were nearby I would say come on by and we can pop it in mine and see if its the tach. You could send it to Palo Alto Speedo or North Hollywood - Pelican also has a rebuild service now that I think about it but its 2 or 300 bucks and it might not be the tach.