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OrangeMax
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Speedometer Pin-out

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
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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.
 

James

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

John Vine
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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
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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
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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
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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 

*driving*Max

John Vine
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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
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Here is a drawing of my current Speedometer pin out

*driving*Max

John Vine
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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
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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