Oil Pressure Gauge Wiring

[AdamQ]

I'm using an old-style oil pressure sender on a recent loom (simply because I had a new and unused spare sitting in a box).  As far as I remember, the white and brown wire used to go from the sender directly to the gauge via the grey plug.  On recent cars, according to the wiring diagram, it appears to go to the tacho and thence to the gauge, changing from white and brown to white and green at the tacho.

I can't check with the ignition on as I'm waiting for the battery to arrive, but with the ignition off there doesn't appear to be continuity between the wires.  Does anybody know what goes on within the tacho with the two connections?  Is there some sort of warning light function?  Or a buzzer or something?  

A simple solution (famous last words) would be to extract the wires from the tacho plug and join them together, but I guess I'm just curious as to why there's been this change ...  Plus I don't want to mess anything else up or create any other problems.

[CharlesElliott]

I’ve yet to fully document this but the wire into the tachometer is a normal voltage feed, but the output from the tacho to the gauge is a pulse (I’ve had an oscilloscope on it) so you’ll need to use the signal going into the tacho rather than the output.

[AdamQ]

Hi Charles,

Many thanks for that.  Extrapolating what you say suggests that the gauges for the 'new' senders are different to the gauges for the 'old' senders in that they expect a pulse signal rather than a steady voltage feed - is that correct do you happen to know?

I'm using an old-style sender with an old-style gauge, but also have a new-style gauge - as soon as the battery arrives, I'll do some experimenting.

Your words 'I’ve yet to fully document this' interest me considerably - does your documenting happen to include a 'conventional' wiring diagram for the more recent cars?  I can't resist asking as such a thing would be of immense use in my opinion ...

Thanks again,

Adam

[Jonathan Kay]

I try to collect all the 7 wiring diagrams known to man... what would you like?

Jonathan

[AdamQ]

Hi Jonathan,

I've got the diagram from the 05.2012 assembly guide that you kindly sent me a while ago.  What I'd really like is a 'conventional' version of that - i.e. one that shows each wire - I'm also not convinced it's complete - e.g. I have a BN wire which I think might be for oil temperature but I can't see it on the engine harness diagram.  Also, the R400 engine harness diagram in particular in the manual appears to be a scan and, by way of sod's law, always seems to lack clarity in any given area in which I'm interested - but that's a minor gripe really and I'll snap out of Victor Meldrew mode now ...

Adam

[Jonathan Kay]

I’ve yet to fully document this but the wire into the tachometer is a normal voltage feed, but the output from the tacho to the gauge is a pulse (I’ve had an oscilloscope on it) so you’ll need to use the signal going into the tacho rather than the output.

Is this the scheme known as "EFI harness"?

Thanks

Jonathan

[Jonathan Kay]

What I'd really like is a 'conventional' version of that - i.e. one that shows each wire - I'm also not convinced it's complete - e.g. I have a BN wire which I think might be for oil temperature but I can't see it on the engine harness diagram. 

I don't think there are any conventional diagrams with wires going point to point for recent harnesses... except for Andrew's beautifully annotated versions. So you have to spot the numerical identifiers.

Caterham do tend to stick to "standard" wiring colours so that can help, but I think that you're past that stage on this problem.

Jonathan

[Richard Price]

'Think you may find that the old sender is simply not compatible with the new loom/instruments.

the old senders are resistive, but I believe current cars use solid state senders with a voltage output.

easiestvwould certainly be to use a sender with an output compatible with the loom and instruments