TimoK

My tachometer is dead. I have now ´79 SC 3.0L engine in my ´71 914 and I use original CDI unit. The tachometer is old used from year 1970. It should work according PO, but I can not be sure.

I tested the black/violet line from the CDI unit, but I didn´t get anything. The engine works fine. What kind of signal there should come out ??? I measured only the voltage between it and ground.

Is there any easy way to test the tachometer ?? Any hints ????

thanks,
timo

Flying Finn

Have you tried w/ some other tachometer? Then you should know if the problem is w/ the actual tach or just wires?

BTW, mukava huomata, etta taalla on muitakin Suomalaisia

si2t3m

Hi conversion friend!

I'm assuming that the 70 tach you are using is for a 6cyl. These tachs need an external ballast resistor as they can't see the signal directly from the dizzy. Sorry.

I had the same issue, I did find an external ballast resistor, but afterwards found a tach from a 72 911 that doesn't need the external ballast. My Purple/black wire is connected to the dizzy. Works great.

HTH

Marc-Andre Morin
70 914-6 conversion 2.2

Paul Brewer

Use a multimeter or a test light to find out if you have continuty in the signal(black/violet wire) line.

The signal, if present, will most likely be less than 1 V, so you will need a multimeter to detect it. If you do detect a voltage chances are good that the problem is in the tach. If you have continuity in the wire but no signal then look more closely at the sensor.

Also, there should be a red or red/black wire supplying 12V power to the tach. Check that too.

TimoK

Thanks all,

I haven´t tested with other tachometer. I do not have an other one. The one I have is from ´70 911 T and it should work.

I didn´t know that it would need an external ballast resistor. Where it should be ?? In purple/black wire between tach and dizzy, or where ??? Is it only a resistor ?? How big ??

I an still worried about the CDI unit. I measured the black/purple wire straigth from the CDI unit with multimeter and the voltage was about 0 V. But, which sensor did you mean Paul ???

The power line for the tach is ok.


Thanks,
Timo

ps. todellakin, hauska tavata taalla muita suomesta !!!

si2t3m

Hi,

The external ballast resistor is a round metal 'can' about the size of a relay but 2 times as high. It's located on the early 911 electric engine console and was also located on the 914-6 relay board (but not on the /4). It has 3 male connector on it. One for ground, and one where the tach signal enters and goes out.

I do know the usual speedo shops can convert your 70 tach to work with the signal directly from the CDI or distributor. (I'm talking about the dizzy because my purple/black wire is connected on it as I have a 3 pin CDI box).

If memory serves me well, we are talking around 150$ to convert the tach. The external ballast goes in the 250$ new. Ouch!

When I was using the 70 tach, the signal was comming from the coil going to the ballast and heading to the tach. Looking closely at the 914-6 wiring on pelican parts and early wiring diagrams from a 70 911 showed me this.

I not sure on when the change was made but I can assure you that the tach I have is stamped 72 and works without the external ballast as opposed to the 70 tach...

Search in the 914 mailing list concerning this.

HTH

Marc-Andre Morin
70 914-6 conversion 2.2

john walkers workshop

an SC tach is the ticket. no resistor required. often those early tachs won't work with the 6 pin SC CD unit.