how do dash guages work?

[WabTheKing]

ok from my vems ecu i have an out put for

water temp, one wire
rev counter, one wire

other wires i need to trace are

speedo wires, does this run through the ecu or straight to the dash on a standard car?? and how many wires

petrol guage, does this run through the ecu?

oil temp/ pressure not too much of an issue, neither is volt meter

how many wires do the guages use to work??? given that i only have one wire outputs from the ecu

cheers
will

[GT500]

They are variable earths, so ecu to gauge , gauge to earth.

All wires are one colour for one job on an Audi.
I think the speedo is purple and white or black, check it on the sender don't go through ecu on my UR
Rev counter is a pulse from coils

Get back to Uni!

[johne]

Water temp, oil pressure, oil temp and fuel gauge all work in the same way. They have a single wire which connects to ground via their associated sensor. This sensor changes its resistance in response to whatever it's monitoring. For some gauges the resistance goes up as the measured parameter goes up, for others it goes down but the principle is the same. All the above gauges are three wire devices, +12v, ground and the sensor wire just described.

The speedo sensor feeds up to the dash instruments and as well as working the speedo is buffered and fed out to many places such as cruise control, rear diff lock etc. Single wire, lilac in colour I think.

The rev counter is a pulse signal with the number of pulses corresponding to the RPM

On our cars with two engine temperature sensors, one for the ECU and one for the gauge I see no point in you using the temp. O/P from the Vems unless you no longer have the sensor on the inlet water rail. Just leave the water temp. gauge as it is.

AFIK the petrol gauge doesn't touch the ECU. Check S2central.com for ECU pinout information.

[WabTheKing]

non of the orginal sensors as changed to a v8 from 3b

[GT500]

non of the orginal sensors as changed to a v8 from 3b

As I said they still will be the same colour! look at either loom...

[TH_Trinity]

To test these gauges, can you put the corresponding wire to ground to get a max readout or will that destroy the measuring circuit?