Speedometer Pin-out

[OrangeMax]

Greetings,

I've acquired a Caterham project car. The speedometer is not working. It gets power. The sensor is gapped correctly and lights up on all trigger wheel teeth. I've dome the ground modification. The sensor wiring harness has 12V incoming, good ground and continuity on the signal wire. I'm beginning to consider that the plug may not be wired correctly. I have a diagram of how my plug is currently wired. I'd post it here, but I'm not sure how to upload the picture to this forum. Below is the pin out:

#1 Green (12V with ignition on)

#3 Black (ground)

#4 Red/White (Dash Lights)

#5 Ground

#6 Red/Blue (Sensor Signal Wire)

I've noticed that on a few wiring diagrams that #7 is used for the Red/Blue sensor wire. Thoughts?

Also where is a source for the 8 pin plugs and the connectors used with them. Thanks!

[aerobod - near CYYC]

It is often the case to use a 1000ohm pull-up resistor on the sensor line, if it is not built into the speedo for a 5V Hall effect sensor input, much like is needed on the RPM feed between the Tach and ECU.
 

[ChrisC]

Yer I was going to say has the resistor been removed, it's common practice with race cars.

[John Vine]

What year/model is the car?  I'm assuming we're discussing a Sigma variant?

Could it be that the sensor is wired into the loom incorrectly?  The connections are usually:

Sensor   Loom

Blue       Black (earth)
Black     Yellow/Black (pulse signal)
Brown    Green (12v supply)

Note that, perversely, the sensor Black is not the earth but the signal wire.

(For info on how to upload photos, see the Forum User Guide.)

JV

[R300 FNL]

I'm rewiring my speedo at the moment. I have the older (2-wire) sensor and was told the red/blue signal wire goes to Pin 7 (red blue) but you have the newer 3 wire sensor so I would say your signal wire is correct and goes to Pin6 (white/black).

Unlikely but maybe someone knows if the red gauge wire Pin3 requires a connection.

The other thing to check would be the calibration of the gauge.

Press the reset button for 2-3 seconds, the LCD will show the calibration number currently set. Each digit within the calibration number will flash in turn for approximately 2 seconds. (my gauge was calibrated to 8380 pulses per mile)

[John Vine]

Re #5:

Good point about the calibration code. 

For a table of typical codes (for a 3-wire sensor driven by a reluctor ring), see Part C of this Guide.

JV

[OrangeMax]

Thank you all for this information. My Caterham is probably unique in that it's mostly homogenization of different years/specifications. The fellow I purchased the car from had it running, and its fast and fun. But there were a few things he had not figured out. The chassis is an Arch motors unit dating from 2006. The wiring harness as close as we can figure might be sigma? The tach, according to the Caterham Dealer I've been working with dates to a Rover K series circa 2002. The engine is a Duratech 2.0, COP, barrel intake and Cosworth ECU. The former owner was building his version of an R400, I believe. 

Insofar as the Speedometer challenge goes. I have checked the wiring on the sensor plug and all the connections are correct. Yes, I agree that the use of the black wire for something other than a ground is a boobie trap. The former owner did create his own wire harness from the sensor to the main harness and he didn't use the factory colors for the wires. So I'm going to need to take the tunnel cover off and see what he spliced his wire job to. There is continuity from the signal wire to the red/blue wire pin #6 on the speedometer plug. Giving the information I'm going to try moving the red/blue wire from #6 pin to #7 pin as the Caerbont  document shows

MAX 

[John Vine]

Thanks for the background info.  In my motorbike days, that would have been called a "bitsa"!

Can you post pics of the speedo  -- front and rear -- to include Caerbont's part number?  That may give us some clues.  

And good luck sorting it all out.  Sounds like a fun project.

JV

[OrangeMax]

Here is a drawing of my current Speedometer pin out

[John Vine]

This is what the Feb 2015 Assembly Guide gives for the Sigma speedo wiring:

 

The signal wire is YB 178, whereas yours is Red/Blue.  But it does connect to pin #7 rather than #6.

JV

[John Vine]

Re #1:

Also where is a source for the 8 pin plugs and the connectors used with them.

You could try MES (Motorcycle Electrical Services) Ltd in Warwick on 01926 499756.   I believe they make a lot of CC's harnesses.

JV

[OrangeMax]

Greetings, Here is the views of the speedometer as requested

[OrangeMax]

Does anyone know the best way to remove the pins from the 8 pin speedometer plug?

[John Vine]

Thanks for the photos.  That's what Caerbont call an Electronic Programmable Speedometer with a 6-digit calibration code (as described in #6).

I've never tried to extract a pin from the speedo connector.  But assuming it works in the same way as an Econoseal connector, insert a thin-bladed screwdriver (a jewellers' one would be ideal) in the space under the pin (see photo) to lift a little retaining tab inside.  Pull the wire from the back of the plug at the same time and the pin should come out.

 

Re wiring, I've just checked my own speedo plug (2008 Duratec) and it's wired as shown in #10.

JV

 

[John Vine]

Did you manage to display the calibration code? 

JV

[OrangeMax]

Greetings John,

Actually no. I tried the procedure and never got the code to display. It will display the miles, trip miles and I can zero out the trip miles, but I cannot get the code to show. I've tried this on both speedometers that I have without success. 

I have been able to move the signal wire from pin 6 to pin 7. Weather permitting I will test that change out today.

M

[L66TEY]

Thank you John - for posting the link to "Speedometers", I'll now be able to address the jumpy speedo and stuck at zero needle issue. 

Chris

[John Vine]

Re #17:

I hope the guide helps. Do let us know if you fix the problem.

JV

[John Vine]

Re #16:

That's very odd.  Are you following Caerbont's procedure correctly?  It's set out on page 2 of this document. Use Method (i).

As you have a KPH speedo, you'll need to use the appropriate code in the KPH table at the end of the Speedometers guide.

Looking forward to the results of the road test.

JV

 

[John Vine]

Re #16:

Weather permitting I will test that change out today.

If the weather's inclement, you could always put the rear of the car on axle stands, select top gear and (with care!) start the engine.

JV

[OrangeMax]

So the saga of my speedometer continues...John, thank you for reminding me of the recalibration procedure for the speedometer. It's amazing how following the instructions works...sometimes. The code displayed was 008359. It did not match anything on the chart so I reset the code to 024581 (Avon CR500 205/55 x 13). I ran the car on stands in gear, no luck. It would not display any speed. I tried the signal wire both in Pin #6 and Pin#7 without success. I again checked to see if I was getting getting pulses at the sensor. The sensor would light up on all 42 teeth of the trigger wheel. I checked the voltage signal wire at the speedometer. it would range from .4V (no light)  to .7V (light on). So I'm really scratching my head on this puzzle.

I even tried a second speedometer I acquired. It also did not display speed. the second unit was curious as it would not let me access the recalibration feature. I have included pictures of it so maybe someone can say if this particular version omits recalibration?

So any thought of what I can try now? If I can't get this working I'm considering having the speedometer converted to GPS. If that is the case I'd like to find a silver faced speedometer in MPH. Anyone have one they don't want sitting on their shelf?

Regards, OM

[aerobod - near CYYC]

The pulsed signal voltage at the speedo is not in the correct range for it to register the pulses. Do you have the 1000 ohm pullup resistor installed between the 12V and signal wires on the speedo (Pin 1 to Pin 7), if it is not confirmed to be internal to the speedo?
 

[John Vine]

Re #22:

Good call. The required 1K ohm resistor is shown in #10. See also #2 and #3.

Your second speedo (black dial, P/N 71255) certainly looks like one that can be programmed via a pulse code, so I'm puzzled that you're unable to display the existing code.  You could ask Caerbont to confirm.

Should you still need a silver-dial MPH speedo, CC have this one with 20% off.  They describe it as KPH but the pic shows an MPH one.

JV

[OrangeMax]

So, try placing a 1 ohm, 0.25w resistor inline on the red/blue signal wire? Ok, I'll try that!. Thank you for the info on the silver MPH Tach. I will contact Caterham on Monday Morning to confirm its a MPH version. Thanks!

OM

[aerobod - near CYYC]

Re #24, the resistor should be placed across the 12V and signal wire, not in-line in the signal wire. What you can do to temporarily test this without cutting any wires is to insert the resistor into the back of the pins in the plug, one end into pin 1, the other end into pin 7.