After hunting around for a "real" period tach for my Volvo project over a few months, I decided to make something that would have the same look, and be functional and fairly inexpensive.
I wound up getting a VDO 52mm tach from a 240 sedan (says Volvo on the face) for more or less free, these can also be found on e-bay for $15-25. Most 240 owners want the large tach that replaces the clock, so these are around.
The housing is made from sch 80 PVC line - the OD is 2.375" - ID is around 2.062" and will fit the tach OD with a bit of sanding (the ID on my section was a little irregular).
I used some 3/8 all thread pipe (used in lamps) to attach this housing to a plate with small nuts (again from the lighting section of your hardware store), and added a small triangular Al. part to support the whole thing.
I ran the wiring thru the threaded pipe and machined tapers and grooves into the PVC to make it look more like the "smiths" instruments optional at the time on some Volvos (and standard on the 123GT) with a turned Al. plate in the back.
None of the above is really necessary BTW, just makes it look a bit more like it should.
The wiring is easy too, One "hot" - one ground - one wire from the coil neg. - and one for the light (I spliced into the heater control light for this).



Cheers!
OK

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that is so very excellent!

so the signal comes from the hot wire ?
or what?

i like that alot very tidy and orginal looking

There are only 4 wires to hook up ...
1 "hot" 12V positive - powers the tach (I used the fused wire going to the radio).
2 another "hot" 12V+ switched thru the lights (I used the heater control light).
3 "Ground" or earth 12V negative (goes to the insturment and light).
4 the "pulse" wire, which comes from the coil. (the same terminal that has the small wire going to the distributer base and on to the points). This provides the signal for the tach to "count".

You may want to hook yours up another way, the radio on my car comes off an aftermarket switch that has no "acc." position.
Also the heater control light circuit on my car is not on the instrument "dimmer" circuit, I never dim them anyway, so not an issue for me.

Cheers!
OK

That's pretty cool looking. A nifty solution if you don't have a pod. I did snag a smith pod tach on eBay a while back, but it's for a 6 cylinder. I'm gonna try to get one of these 52mm tachs from the local pick-n-pull this weekend and fit it into the pod.

My real question is... what the heck is growing on your dashpad?!

Somewhere , down in my cave, also known locally as "Volhalla", I have one of those Smiths 6 cylinder tachs. Upon removing the end cap from the unit, it seems to have a possibility of switching from 6 cylinder pulse to 4 cylinder. Got lotsa "4's", but no "6's" (except the Sugga, and that's not an option!)

I am not a brave person when it comes to electronical stuff, having let the "smoke" out of too many things. So, seeing as I could only have one shot at any alterations, I'd prefer to follow someone elses guidelines. Any ideas?

If you have a switch or jumper that is marked 4/6 you should be able to check if the tach works properly after moving the the tach to the 4 cyl. position.
If you have it hooked up correctly the worst that should happen would be an inaccurate reading of the rpm's.
http://www.egauges.com/Inst_PDF.asp#Tachometer Might be of some help.
I used the number 0-515-012-044 pdf file, you won't be able to follow it exactly because it is for a VDO instrument but it may give you some ideas/help.
There may be something similar for the smiths instruments, British car sites may be helpful too.

Cheers!
OK

Well Jack, that is called Indoor/outdoor carpet. It was purchased for my boat, but I had some left over! Where I live, nothing is going to survive the Summer so I opted for this, as I have some more and it, and it is replacable.
If this is not OK, then I have other options, not like head gaskets!

Cheers!
OK