Sat nav speed sensing

[Patfallon]

Hi does anyone know the right wire to connect to for speed sensing on sat nav. is it behind the instrument panel or can it be found in the centre console / cruise. 1988 5.3 convertible vin 150014. thanks.

[Mark_B]

Hi Patfallon a warm welcome to the forum.

I'm pretty sure a satnav calculates your vehicle speed from the decoded satellite signals, coming down from 'up there'.

Maybe you'd meant the lights sensing? (for night dimming) That's either of places mentioned.

On my TomTom Go300, I select 'display speed' in a menu somewhere.

[Patfallon]

Thanks Mark you are correct they do download from satellite, however, plumbed in versions of sat nav can also be connected with a speed sensor, either mechanical connected into the speedo drive cable, or, where there is an electronic speedo into that wiring. the benefit is that when you go through tunnels or for other reasons lose the satellite signal the navigation still reads your speed and estimates your tracked position. when the satellite view returns the pick up is almost immediate.

[greeban]

That's very clever! Was using my portable sat nav on the train the other day - got to 128mph. Quite impressive for 'British' railways.

[dhdove]

Graeme

That's all very well, but what did you do in the tunnels?????

DH Dove

[Mark_B]

Graeme was maybe looking for somewhere to pick up a speed signal from the revolving wheels?

I must admit I'm getting far too dependent on my satnav, I sometimes get lost when in tunnels, luckily I can follow the other cars and find the exit.

There's a speed signal that's fed to the back of the Trip Computer, in amongst the wires going to it, not sure which one. It's 5V 'TTL' signal levels electrically compatible with lots of things.

[Patfallon]

Mark I appreciate that I'll pass the info on to the audio man tomorrow when I get my new Becker, looks bland, dull, boring, uninspiring, made for german cars audio unit. But the thing is, its bloody brilliant and for that reason alone it gets to go in the cat.

[Patfallon]

if anyone is interested, the yellow wire to the back of the computer is the one to connect to and it all now works a treat. thanks for the info