Bouncy lagging tach

[AcampoDave]

Pretty much like the title says. It bounces up incrementally as I wind up the motor. It also reads low most of the time. I've swapped the tach (Autometer) with another identical version. I've swapped the coil, I've tried a different ground. Tomorrow I'm going to swap the trigger wire to the HEI and I'm wondering what guage wire I should use for that as well as the 12V hot. I think it's all wired with 18 guage now. I can't think of anything left to try besides that, but if anyone has a suggestion please let me know. Thanks.... oh and I'm sure the tach itself is set for 8 cylinders too.

[Willshook]

Is the HEI getting a clean, direct 12V?

Does it steady if you turn on the headlights?

[raggedjim]

Maybe this would help?

https://www.youtube.com/watch?v=-6j3glUtecY

[AcampoDave]

Thanks for the replies, here's an update: I swapped the 18 guage sender wire from the HEI with a 14 and nothing changed. (The HEI is powered with a 12 gauge wire right from "ign hot" on the fuse block and the motor runs great so I believe my power wire to be strong.) I also doubled down on my ground by adding another wire to a firewall location which now compliments the original ground at the dash, still no change. I tried with the headlights on too and again no change. Really all that's left is adding the resistor so I'll get one next time i order from Amazon. I think my pigtails and plug at the distributor is good, (it's an Accell) . I looked it over when I change the sender wire .

The needle never bounces above my actual rpm. What it does instead is lag towards the lower side and bounce to catch up with the real rpm under acceleration. At a cruise, It also just reads plain low like I have an imaginary overdrive at highway speeds.

[AcampoDave]

I messed with the connector at the cap, it worked good, for a few minutes, then back to the same . Then I removed the Accel connector and put 2 separates for batt and tach.....nope. Lastly I gave up, put my original coil back in and it worked right again. I drove a while and it kept working. I read on line that I need dielectric grease on that rubber washer below the coil and I don't have any and its dry, so I guess I'll put some on there another day, but it's fixed for now and I don't know why.