'78 spider - Tachometer rebuilds

[MrBlimp]

I just continuity tested the (Brown) wire off the middle terminal of the tachometer (it is patched into a Red wire which terminates at the coil but is not connected to anything - in fact, when I first started working on the car it had a long plastic junction device on the end acting like a wire nut/cap)

Since my tach won't work if I connect a wire direct from that terminal to the coil my guess would be that the tach is shot!

Any rebuilders out there?

Has anyone rebuilt one on their own and can supply some "fix" direction?

[spider2081]

Have you confirmed you have battery voltage on the + terminal on the back of the tack or the Yellow/black wire on the nylon connector?
Do you also have a ground on the white/black wire at the connector? The ground is shared for the internal dash lighting and the Tachometer section of the instrument.
If you connect a volt meter to the brown or brown/white wire at the tachometer connector while the engine is running do you have a voltage that is lower than battery voltage?? When the car is cranking but not running some meters will indicate a pulsing or changing voltage if the wire is properly connected to the coil - terminal.

One publication I find helpful to read is the Fiat publication "Spider 2000 Electrical Diagnostic Manual 1980-1981" Although it is not exactly for your car the principles of troubleshooting and the majority of wire diagrams are very close if not the same. You can find the manual on line and download it.

[gchocevar]

For what its worth, I documented the wires to the front panel from the connector kit on my 79 Pininfarina 2000.
I also had a problem with my instrumentation from a shorted IN4004 diode behind the gas gauge. It seems some of the wires to the front panel may not follow the same color convention as on the other side of the connector (the color which is shown on most of the electrical diagrams.)

Good luck

[kilrwail]

To answer the OP's original question, Palo Alto Speedometer is a reputable instrument specialist, recommended in the Porsche world. Probably not cheap.

[RRoller123]

Palo Alto Speedo is excellent! They repaired my clock and turned it around in less than a week at a very fair price.

[MrBlimp]

For what its worth, I documented the wires to the front panel from the connector kit on my 79 Pininfarina 2000.
I also had a problem with my instrumentation from a shorted IN4004 diode behind the gas gauge. It seems some of the wires to the front panel may not follow the same color convention as on the other side of the connector (the color which is shown on most of the electrical diagrams.)

Great diagram - Thanks.

This seems to match my system. It would be great to know what the three wires are supposed to do and go to. That seems to be where my problem is. Especially since the brown wire doesn't currently connect to anything nor match the wire coming off the coil. I am going to try the other suggestion of connecting to the opposite side of the coil and see what happens.

[MrBlimp]

Have you confirmed you have battery voltage on the + terminal on the back of the tack or the Yellow/black wire on the nylon connector?

YES

Do you also have a ground on the white/black wire at the connector? The ground is shared for the internal dash lighting and the Tachometer section of the instrument.

I believe so but will recheck

If you connect a volt meter to the brown or brown/white wire at the tachometer connector while the engine is running do you have a voltage that is lower than battery voltage?? When the car is cranking but not running some meters will indicate a pulsing or changing voltage if the wire is properly connected to the coil - terminal.

There is nothing on this wire as it wasn't connected to the coil - when I did connect it to the side of the coil as shown in wire diagrams I had a stead 12 volts.

One publication I find helpful to read is the Fiat publication "Spider 2000 Electrical Diagnostic Manual 1980-1981" Although it is not exactly for your car the principles of troubleshooting and the majority of wire diagrams are very close if not the same. You can find the manual on line and download it.

Where can I get this book - I looked on line and can't find a copy anywhere.

[spider2081]

Its on Mirafiori.com in the library. You have to be a registered member of the site and signed in to access their library.
Another location is www.njfiats.org Look under pull down menu "resources" then "Manuals & Guides" its a little over 1/2 way down this list.

when I did connect it to the side of the coil as shown in wire diagrams I had a stead 12 volts.

With the engine cranking and not running the - side of the coil should be a pulsing voltage. With the engine running the voltage should be less than the battery voltage. The higher the rpm the closer to battery voltage, the slower the rpm the lower the voltage and the more visible the pulsing should be. This is with the meter measuring DC volts. Not all meters work the same but this is worth trying.

The + side of a ignition coil connects to the ignition switch and is a constant voltage. The - side of a coil connects to the points or the ignition control module which ever you have. The tachometer connects to the - side of the coil as that is the side switching between ground and open to create your spark and drive the tachometer.

[MrBlimp]

Its on Mirafiori.com in the library. You have to be a registered member of the site and signed in to access their library.
Another location is http://www.njfiats.org Look under pull down menu "resources" then "Manuals & Guides" its a little over 1/2 way down this list.

Thanks

With the engine cranking and not running the - side of the coil should be a pulsing voltage. With the engine running the voltage should be less than the battery voltage. The higher the rpm the closer to battery voltage, the slower the rpm the lower the voltage and the more visible the pulsing should be. This is with the meter measuring DC volts. Not all meters work the same but this is worth trying.

That's what I assumed only NADA

The + side of a ignition coil connects to the ignition switch and is a constant voltage. The - side of a coil connects to the points or the ignition control module which ever you have. The tachometer connects to the - side of the coil as that is the side switching between ground and open to create your spark and drive the tachometer.

I tried both sides of the coil same NADA (and registering a steady 12 volts all the time)

[spider2081]

I tried both sides of the coil same NADA (and registering a steady 12 volts all the time)

This is strange. The - side of the coil needs to be connected to ground ( which it is when the points are closed) and then open when the points open this is when the coil produces the spark. So looking at the distributor cam one can see the points are closed for mor time than they are open. This means the ground is present more time than not. This should cause the voltmeter needle or digits to pulse when the engine is cranking and not running. If you have a constant voltage on both sides of the coil I don't see how you are getting a spark to run the engine.