Tach install

[TRIX]

Hey. I'm installing an Autometer tach in the Rally car. 1.8t 2000. Does anyone know where to tap in for the tach signal?

Thanks

[MyOtherRidesAVette]

Would this be the lead coming from the Speedometer Vehicle Speed Sensor (VSS) that services the ECM that services the dash tach? That is the only related component tied to that module that I can find. It's a .5 mm² white wire with blue tracer at the VSS and a .5 mm² yellow wire at the ECM.

MORAV

[dmbluebeetle]

The VSS is for just the Speedometer and Odometer. If you tried to use it you would have no Tach reading every time you stopped the car. It might be better to pull the cluster and see what wire is used for the existing Tach and tap off of it.

[MyOtherRidesAVette]

Makes sense to me, and if I had thought about it....

I didn't/don't know what component measures the engine rpm. Haven't been able to find it in the Bentley (this is the information that came up when going to the tach wiring diagram), and could not find any other component attached to the ECM for the tach that would be related. There is one lead, that when clicking on the tail, to take me to another diagram, doesn't. Maybe that's the one.

What component does measure the engine speed. Old skool tachs were attached to the low tension side of the ignition coil, today...?

In doing a little reading, "today the signal for the tachometer is usually generated from an ECU which derives the information from either the crankshaft or camshat speed sensor". Find this and problem solved. Dismantling the instrument cluster is a bad way to do this mod.

I can look later for that sensor.

M.

[dmbluebeetle]

I would think the ECM would have the Tach output to the cluster.

I haven't seen the backside of a VW cluster yet, so I don't know if there is a cover on the back that could be removed to see the circuit board to follow the trace back to the connecting plug to find what wire occupies that slot, which then you could tap into that wire.

[MyOtherRidesAVette]

I haven't found any wiring diagrams for the ECM to cluster, they are shown as one in the Bentley wiring diagrams for the systems, and besides the signal being sent from the ECM, may be modified from the signal coming from the CSS.

Well, now that I think about it, I haven't found schematics for them, but I did see the two 30 pin connectors diagramed somewhere, so I guess I can find THE wire.

M.

[dmbluebeetle]

My first guess would be a pulse width modulated wave form coming from the ECM to the Tach. The Speedo & Odo use that type of signal to operate with.