What's wrong with my tach?

[fmicle]

So I got this SunPro Mini Super Tachometer II and installed it a couple of months ago. Everything went fine, got illumination and all.

After a while I started noticing that sometimes the needle wasn't moving when it should have been... So I kept an eye on the problem. Here are the observations I made so far.

If I turn the key (switch off the engine) too quickly, the needle remains at whatever RPM there was when I started turning the key. If I stop at in the ACC position I can wait for the needle to (slowly - 1-2 secs) come down to zero. I don't know if that makes a difference for the actual problem described below.

Symptoms:
- I turn the key from OFF to ACC, the needle jumps from zero (or wherever it is) to 1 (1000 RPM) even though I haven't started the engine yet.
- When I actually start the engine, the needle jerks a little, but remains stuck at 1. No matter how I rev the engine, the needle doesn't move.
- I shut off the engine, turn the key back all the way, the needle goes down to 500 RPM and stays there even if I take the key out.
- Usually during my 25-30 min commute, the tach eventually starts working correctly. I never caught the actual moment and how it happens, but I just at some point notice that everything is alright.

Does anyone have any ideas? Theories? Has anyone experienced anything similar? I have no idea what could be wrong? Some kind of static charge built up somewhere? No idea, just guessing here... I tried tapping, light and hard, it didn't help.

[AlexNet0]

check that your splice is solid on the RPM wire, and then see if the tach has a warantee on it.

[Liu997]

Yea my sunpro tach does the same thing and I heavily soldered all the connections. But mines usally does that when it rains, Im starting to give up on sunpro tachs.

[AlexNet0]

Ive had my sunpro 3" tach stuffed into the drivers side center column cubby since I bought the car in May 07 and 75k miles ago, I havent had any issues with mine.