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DRE shift light not showing revs - thoughts?


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  • Support Team

So, having some trouble getting my DRE Shift Lights to show anything.  This is the situation:

  • Power is fine - I switch on the igntion and it lights up, I can apply the settings and they stay there once I have switched off the ignition and the cut off switch.
  • I'm pretty sure that I have the right cable for the rev signal.  I've chopped the white with black stripe cable in the tacho loom - with that wire cut the tacho doesn't show the revs when the engine is on, and when I have the two ends plugged into a block (for ease of diagnosis - I'll crimp it all properly once working) the tacho works again.  With the green DRE cable in the same block the tacho works (so there must be a good connection in the block), but the shift lights remain resolutely dark.  Pretty sure that the green DRE cable is plugged into the block fine.
  • I've set the low point (i.e. the point the first lamp lights ) at the lowest point (2600 RPM ) and have taken the engine revs over this but the lights don't come on (I'll change that to much higher that when I know its working).
  • When I check the max RPM value that should be stored in the memory, its 0000
  • The only thing that does seem to happen is as I take the engine over 2600 RPM the number '6' appears briefly on the LCD display, then goes out again.  

From that, there are a few possibilities I guess:

  • The unit is broken somehow
  • I haven't sorted the earth properly - I'm connected into a black wire and the unit seems to be operating with power, but maybe the earth isn't good enough and is interfering with the pulse signal
  • The wire isn't actually the right one - it performs another function and the tacho not working when it is cut is a co-incidence.

Other thoughts?  I'm going to drop DRE an email to ask them as well.

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Bit late now since you've cut the wire but as mentioned above take a look behind the dash to the far right, lurking behind the light switches in my 420R, were a set of spare set of the required power, earth and signal connections, presumably in the loom for when a factory fitted ACES unit is used.

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  • Support Team

Unfortunately there wasn't a spare wire for the signal (see photos in this thread: https://www.lotus7.club/forum/techtalk/posi-tap-connector-wire-dre-shift-light) so I had to chop into the tacho loom.  There were spare wires for power and earth though so I've used them.

I'm pretty sure that I have the right wire (in that its white with a black strip, following the standard car wiring colours) and that when disconnected the tacho stops showing the revs and when connected it does.

I'll try setting it to one cylinder as suggested by Richard above.

Any other things I could try in my search for a solution?  Could my earth connection be poor, or would the DRE unit not switch on at all if that were the case?

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  • Area Representative

I found the information I sent to DRE when i got mine working on my Sigma way back 7 years ago!:

Car                         Caterham RoadSport SV 150BHP (1.6 Ford Sigma) with a standard Caterham fitted Caerbont Automotive Tachometer


Connections       Red in the DRE to Green

                                Green in the DRE to White with Black tracer

                                Blue in the DRE to Black

                                All the connections are in the multi-plug behind the tachometer


Set the DRE to 4 CYLs but with Stall not activated


Initially I didn’t think it was working correctly because I couldn’t get the revs to display on the DRE (held down the UP button while turning on the ignition) eventhough it displayed 0000 initially it then went blank.


Checked the unit by lowering the first light to come on at 2600 and this proved it was working correctly.

Hopefully these will assist!!

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  • Support Team

Thanks Macca - I think I have stall activated so will try switching that off.  

Its definitely connected to white with the black line (see pic below, not the one I'm holding but the lower one between white/brown and white/green), and I have it at 2600 but nothing is coming up when I take the engine revs up over that.


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  • Support Team

So, the one cylinder setting seems to have done the trick.


Annoying, but at least the lights seems to be working. I have to put the proper connections in now (swapping the blocks for proper crimps etc) and then take it on the road before I'm sure.


What still doesn't work is the max revs display. Apparently my max revs so far is....... 6. Yes. Just 6.

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  • Support Team

It's a nice to have rather than anything vital.  The idea of the max revs recall is that if you say missed a gear on track, you can look back when you're back in the pits to see just how high the revs got to guage potential engine damage.

Useful for those of us with less than Hamilton-esqe track skills!

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