Signal Isolators(?)

[Gingerbread Man]

Right.

I brought a shift light for my Cat.
Everyone else who brought theirs tapped into the wires going to the tacho, earth, live and the signal feed.

Fine I thought and followed suit. I seem to be the only one who has problems when doing this. The RPM signal doesn't seem strong enough to be able to supply the shift light and the tacho. My tacho goes sporadic and doesn't read correctly.

I've checked and double checked the connections and all are fine. Correctly crimped with male, female and piggy back crimps. The shift light detects the signal and lights up, so it's getting all the right boxes ticked.

After a bit of researching my problem, I've read about similar problems and that a signal isolator (?) is the answer. This would hopefully let my shift light and tacho work in harmony.

Now, thinking that it would be easy (and it should have been) to connect up, the talk of signal isolators and the lark is out of my depth.

I've looked into local auto electricians, but with the prices I've seen, one hour of their time is basicly the cost of the shift light(£60). This doesn't make it worth going to a local pro. So I hoped that someone knowledgeable would be able to point me in the right direction, either with the guidance of making a signal isolator for me, helping me to cobble together one or any alternative would be fantastic.

I've drilled a hole in the scuttle for the wire to go through now, so I've got to have something there to serve the hole a purpose, working or not!

[Gingerbread Man]

Where does the signal for the RPM come from on the VVC. The ECU or the coils? If the coils, I hope I might have a lead.

[Colin Mill]

Hi

I'll have a look at the Circuit diagrams that came in my build manual (circa 2004) and see what might be needed.

What year is your car?

[Gingerbread Man]

Hi Colin.

Thanks for your reply. The car is a 1999 Rover VVC.
I have a few circuit diagrams I could email over if they would help.

[Colin Mill]

Good - If you google "CSM gyro" it will give you a link to our company site and the email is on the about us page. Any info on the shift light you might have would be handy. I'm sure some simple buffer/isolator will do the trick.

BTW - with the original connection scheme where the taco went nuts - did the shift light seem to work OK or was that misbehaving too?

Edited by Colin Mill on Saturday 2nd October 11:00

[Gingerbread Man]

YHM Colin.

[Colin Mill]

Many thanks - I have all the info you sent. It's a small world - the shift light company is about 5 miles from here!

[Fred Gassit]

You could try a 10K resistor from input to Ignition.
IIRC my ACES shift light needed this to work properly.

[Gingerbread Man]

Fred Gassit said:

You could try a 10K resistor from input to Ignition.
IIRC my ACES shift light needed this to work properly.

Hi Fred.

How did you fit this in? Just barebones in line?

I don't understand where you have fitted it? I have signal, live and earth connections which go to the tacho. I tee off these to go to my shiftlight.

[Fred Gassit]

My experience is based on a 2002MY 1.6 K-Series with standard MEMS engine ECU and Caterham electronic tacho.
Looking at the circuit diagram for the 2001MY reveals the tacho has the following connections:
Black = GROUND (0V)
Brown/Yellow = GREY ENGINE PLUG Pin 11 (I guess this is the Ignition warning light signal)
Red/White = LIGHT SWITCH (Illumination feed)
Blue/White = HIGH BEAM WARNING LIGHT
Black = GREY ENGINE PLUG Pin 6. Not connected. May be Supersport Shift Light.
Green = IGNITION FUSED FEED
Green/White = INDICATOR SWITCH
Green/Red = INDICATOR SWITCH
White/Black = GREY ENGINE PLUG Pin 2 (I guess this is the engine speed signal)

Hence I think you need to connect your 10K (10 kilo-ohms) resistor between the green wire (IGNITION - should measure steady 12V with Ign ON) and the black/white wire (ENGINE SPEED SIGNAL).
Please solder the joints and use heat shrink sleeving! (Not Scotch-loks and insulating tape... Urgggh!)