Factory Tach Issues.... Looking for some Help

[Six862m6]

Hey guys, looking for some opinions on what the deal is with what I believe is a factory tach connected to an aftermarket (Accel) HEI ignition on my truck. Pretty sure I've got the real deal; the gauge itself looks correct, just replaced the original printed circuit last night (due to half the cluster lights usually not working, but sometimes) and it had the correct cut out area for the tach as well.

My issue with the tach is that it usually doesn't work, but sometimes will perfectly. Then it will work, then not work... like a loose connection. The connections aren't loose though! Do I need to install an electrical filter that I've seen on some of the parts vendors' websites? I've read about them being really sensitive to not having a good ground; I have it ground to the parking brake handle mount/steering column to dash mount (my truck is a '68), so I would think this would be a pretty good ground location? Guess I could always take a jumper cable and hook it straight to the battery ground to test, haha! Any suggestions? Do you think the gauge is just slowly going out?

Also, there are 2 small light bulbs behind the tach gauge (same bulbs, sockets as the rest of the guage lights). What the hell are these for???? They don't seem to do anything and I couldn't see them being "dash lights" as the tach is never actually connected to the printed circuit, meaning they would have to take their power from the regular 3 wire tach connection and would be on at all times. There are no cut out holes in the front of the tach face as a "warning indicator" (think temp/brake on the fuel gauge).... so what in the world????

Lastly; this is not tach related but a question nontheless; what is everyone's opinion on defrost vent hosing. (Non AC Truck) The PO replaced the ones in my truck already, I'm almost certain. It looks to be a plastic material and way too new looking to be the originals. Plus I think the originals were a cloth material, right? My problem with them is that they don't clamp to the defrost vents or the heater box toward the floor worth a CRAP!!! Is there any out there that does or should I just resort to using a few staples or very small screws to keep these things connected properly? What are your guys' experience with this?

Let me know any words of wisdom, thanks!!

David