problem with new caerbont speedo

[pensioner]

My 2003 7 speedo has always read 10 mph higher than the car is traveling. After contacting Caerbont,I tried re setting the dip switches to no avail, and after messing about they suggested I replaced the speedo with the latest version so I ordered one.

I thought that this would be a relatively painless change, but after fitting it, and trying to calibrate as per the instructions, 

I tried to calibrate using the Drive to set facility, and although I could access the DTS screen, and select the 00000 option, after driving one mile, the display remained at 00000 and then reverted to set ppu. In addition, although the needle twitches, it did not deflect full scale when switching on while pressing the reset button,  and although there is a default set of 008380 the needle does not move when the car is driven.

I went back to Caerbont, and they told me that they thought that my speedo was driven from a gearbox mounted speed sender.  This is an unusual sender in that it requires a 470 ohms resistor to be fitted from the speedo signal input to ground.

They sent me a resistor, and along with some other work I asked Tom New he could fit the speedo for me.

After wiring in the resistor, ~Tom has has had about as much luck as I did.

Before i give up and send the new unit back, is there anyone who has done this or is able to offer any suggestions.

Many thanks

[Jonathan Kay]

Do you have a gearbox or a wheel driven sensor?

Did the previous unit work consistently even though it was inaccurate?

Jonathan

[SM25T]

Certainly on my electronic speedo from 2002 there are 4 internal switches but also a small potentiometer inside, which I understand can be used for fine tuning.

[pensioner]

Yes the old one is fine, and its driven from the gearbox

 

[Jonathan Kay]

Have you got:

1. The wiring diagram for fitting that resistor? 
2. The Workshop Notice on improving the wiring? (Can't remember if that includes a test routine.)
3. The original speedometer, and when did you last test the sensor and wiring by reinstalling that?

Jonathan

[pensioner]

Hi Jonathan

I don't have a wiring diagram for the resistor, only that it has to be mounted from the speedo signal input to ground

I dont have these

WN460 - Rear ARB and Wheel-speed Sensor

WN572 - Speedometer sensor groundwire installation

And the original speedo was re installed and working after I couldnt get the new one to work in February, and has been in situ and was working up until yesterday when in went into the garage, so I am pretty confident the wiring is ok

 

[Jonathan Kay]

I'd ask John Vine for a copy of WN572.

There's a related post about matching the sensor and speedometer from ChrisC.

And the original speedo was re installed and working after I couldnt get the new one to work in February, and has been in situ and was working up until yesterday when in went into the garage, so I am pretty confident the wiring is ok

I see what you mean, but it's also possible that something blew during the work.

Jonathan

PS: it's great to get quick direct answers! :-)

[pensioner]

The resistor supplied by caerbont was 470 ohm, the one shown is a 68 in chrisc post.

 

I guess we wont know if the installation was damaged until tom refits it tomorrow.

Thanks for your suggestions

 

[Rex]

My story is very similar. My 2002 car initially read 20% high. I flipped the four switches and that reduced the error to 10%.    After reading so many horror stories, I finally came up with a solution.  Many of my solutions seem to be crude and this is no exception. I located some stick-on numbers that came very close to matching those on the speedo face. I used 20, 40, 60, 80, 100. I moved these all 10% to the right and was able to cover up the old numbers by placing the new ones on the glass. O.K. it's not a work of art--but it is perfectly accurate. I wish I could send you a picture. Unless you were looking for it I doubt you would notice it. Laugh if you will, but I finally know what speed I'm travelling!

[SM25T]

Have you tried adjusting the internal potentiometer Rex ?

[Jonathan Kay]

Laugh if you will, but I finally know what speed I'm travelling!

I wouldn't laugh at all. The Letraset method is excellent if you don't want to go through a full calibration for any reason.

Jonathan

PS: The ergonomics of display of speed in many cars is very poor in addition to the inaccuracy.

[Rex]

I couldn't find the potentiometer.  Maybe mine doesn't have one. If I had found it I probably would have made matters worse. Simple solutions for simple minds I guess.

[pensioner]

Thanks to Caerbont, we finally got this resolved.

My K series has two wires from the gearbox sensor, a red and blue which is connected to the output from the gearbox sensor on one end, and to pin six on the speedo plug on the other.

The  other wire, light green, needs a 12 volt supply, which Caerbont added to the internal wiring in the speedo connected to pin 8.

They also added a 470 ohm resistor between pin 5 and pin 6 as that is also required for the gearbox type sensor.

 

 

[Jonathan Kay]

Did they give you a wiring diagram?

Jonathan

[pensioner]

Hi Jonathan

Its not quite that simple, certainly from someone who has only a basic understanding of electrics.

The speedo is actually now wired exactly as the K series circuit diagram https://www.graduates.org.uk/docs/201626_EU3_wiring.pdf

However that only works because Caerbont have  added the internal resistor and a 12 v feed out from pin 8 of the gauge.

As I understand it, the gauge is wired and configured differently depending on the sensor, ie gearbox or wheel.

The resistor could be fitted externally to the gauge, and I suppose it wouldnt be difficult to wire in a 12v supply, if you understand what was required. The installation would be different however with a different sensor.

Hope that makes sense

 

 

 

[Jonathan Kay]

Thanks

Jonathan