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Spitfire Spitfire Electronic Tach Conversion

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TheAssociate

TheAssociate

Jedi Hopeful
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Hello, all.


Just wondering if anyone out there has any good ideas about how to hook up an electric tach in a Spitfire that originally came with a mechanical drive tach.

I've got as far as understanding that one of the wires of three is ground, one needs to go to the negative side of the coil, but the other wire is a mystery to me. If you look in the Haynes wiring diagram it says that the third wire(going into the tach)is common to the brake light switch, and hazzards among other things and I don't know the easiest way of tapping in, and why I need to.

Has anyone else done this?

Thanks.

Adam Hendrickson
 
I did this conversion with an AutoMeter unit, but frankly do not remember what I did. At the time I called AutoMeter and thier tech guys got me straight. Try calling or emailing your tach manufacturer.
 
Looking at the instructions sheet for the AutoMeter electronic tach I have waiting to be installed, the three wires should be 1) negative/earth, 2) -ve side of coil, and 3) using a fused wire, tap into a 12V circuit controlled by the ignition switch, so you actually get power to the instrument.

Hope this helps,
Mark
 
Thanks for the reply. I am trying to install a late model Spitfire electronic tach into an early model engine that had mechanical drive. The reason is there seem to be no mechanical drive tachs rebuilt available.
Do you happen to know which wire goes to the negative side on the coil? Is it the round connector or the blade type on the back of the tach? Just don't want to fry it....

Thanks.

Adam Hendrickson
 
Thanks. I have a mechanical tach that's perfect, but I cannot plug it into the distibutor. The distributor I have does not have the tach drive. My options are either get an electronic tach and get it working, or pull the perfectly good distributor out of the car and try to rebuild an old Delco tach drive model. I think I'll try to figure out this electric tach issue!

Thanks,

Adam Hendrickson.
 
Adam, if you are going to install the electric tach make sure of several things.
1) The hook up you describe in your early posts above is for an RVC (voltage pulse) sensing tach. Make sure the one you have isn't an RVI type (current sensing). RVI or RVC should appear somewhere on the gauge face.
2) I wouldn't expect a coil wire to be behind your dash since the car originally had a mechanical tach. You should plan on pulling a new tach sensing wire through the firewall and to the coil. You want to connect it to the spade terminal that has the wire going to the distributor (usually a white/black wire).
3) Don't get hung up on the power connection. Find a 12v line that turns "off" when the ignition switch is off. Most of the green wires will fit that description. (Just make sure you aren't tapping into the 10v supply leaving the voltage stabilizer). To be safe, you may want to put an inline fuse on that switched power connection to the tach.
 
Thank-you, Doug.

I appreciate the tip. Do you by any chance remember which of the two terminals on the back of the tach go to the distributor? And which goes to the common positive? There is one terminal that is obviously ground, the other is a spade terminal, the last is a round connector.
I can see I'm going to have to put at least one fuse in line here!
Anyway, I think I will stick with the late style distributor. Seems to make more sense.
I had another thought that I could simply use the battery side of the coil for the positive lead going to the tach. What do you think of that?

Thanks,

Adam H.
 
O.K.

Well, I hope this helps someone else out there. I successfully exchanged tachometers. As I mentioned before, the early Spitfire has a gear driven tach, late models have the electronic tach.
My motivation for doing this is that there are no new distributors available for the mechanical drive tach. The later system is better anyway.
The way to hook the electronic tach up is simple. However it is not mentioned anywhere that I could see as to which wires go to which terminals. I came to the right conclusion based on a hunch from looking at a diagram in the Haynes manual.
The round terminal on the back of the tach goes to the negative side of the coil(-).
The blade terminal on the back of the tach goes to green wire in car(12V,common), or the positive side of the coil(+)(10V).
Then, you must ground the chassis of the tachometer. There happened to be a ground from the old mechanical tach there for the instrument light.
Either of the three sources will work fine, and give a accurate reading from the tach(battery 13.5V, coil 10.5V, green 12V).

I love it when a plan comes together!

Adam Hendrickson.
____________________________________________________________
1972 Triumph Spitfire.
 
I'm glad you got it working. I'm sorry... I didn't check back on this thread to see that you posted more questions. I would have replied if I'd known.
 
No problem,

Thanks for your help - you got the gears turning.

Adam H.
____________________________________________________________
1972 Triumph Spitfire.
 
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