I thought it would be appropriate to start a new thread on this as things have progressed past the original thread, link to that is here.
I have finally had success in getting one to work and work well, the tach being a sierra marine tach but it is full size.
It is the heavy duty series part #82288P , 6K tach 3-3/8" all sierra marine gauge faces will withstand 6 psi water pressure and not leak.
However the gauge is open in back to breath so it must be mounted in a gauge cup, I purchased this one.
More on sierra marine gauges can be found at http://v3istruments.com
Using the pulse settings switch on the back I set it for 4P 8cyl. and tied into the cam pos. sensor with a soldered connection on the terminal in the plug under the seat.
There is a potentiometer on back as well and I used it to fine tune the tach but was only able to get it to within 100 rpms of actual, I will check it again when I get the gauge cup and mount it (batteries very weak on hand held tach).
It is rock steady with no needle bounce and very smooth as I throttled up, this tach will not work using the alternator hook up as it only goes up to 12 pulses but I did order the diodes and resistors to do a DIY tach adapter so I will try that as well and post the results.
The tech I spoke with at V3insturments was very helpful and informative (these gauges are made in the USA!)
Now for VDO tachometers - This gets even better!
My friend in the marine biz is trying locate this VDO marine tach, https://www.vdo-gauges.com/instrumen...ev-signal.html
They come in 2,3 and 4 pulse versions 899-S-2P , 899-S-3P and 899-S-4P seen here https://www.vdo-gauges.com/instrumen...chometers.html
these 3 are 100% waterproof so a torrential down pour will not effect them at all period, they are made in Sicily and John at VDO tech support (also very helpful!!) explained that they can be programmed at the factory to however many pulses you like
So good bye tach adapters!! (1 pulse = 1 wire & 1 coil ), or for "C" models tach lead in headlight bucket!
These tach are supposed to be accurate to + or - 2.5%, only draw back is no potentiometer for fine tuning...
I will post more when I do the final hook up and locate a VDO tach
Special thanks to: Drag Specailties ( for extremely poor customer support and cheesy tachs) , Baron Custom accessories (for twitchy jerky unreadable tachs they guaranty to work on a 03 1800c but good support).