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anthonye81 05-05-2009 08:51 AM

Finding the elusive VSS
Hello there

I am really interested in the MPGuino, but first of all I wanted to know if there is a universal method to finding the VSS cable/s in any car with electronic ignition? I have a 1995 Alfa Romeo 146 with the 1712cc 16v boxer engine, a car which is not well documented, I don't think it was sold in the US. The only specific information is that the OBD has a Bosch protocol, something prior to version M.2.10.3.

So you can see I don't have much to go on! Is there any hard-and-fast tricks to find the VSS cables, such as tracing them back to the speedometer? I haven't pulled the dash out (yet). I noticed on the MPGuino wiki there was a line saying...

Originally Posted by
For finding the VSS hookup, there are several approaches, but at the bottom of Technical Support is a tool that might help you identify the VSS wire location and color

I've know idea where this Technical Support is. That's why I've come to you guys! Any suggestions would be appreciated, thanks.

dcb 05-05-2009 09:20 AM

There are some links at the bottom, one is to a rostra site that sells a cruise control device in the states, but there are no alfas in it.

Can you locate a schematic for your car (online picture or manual) and post it?

i_am_socket 05-05-2009 09:23 AM

After some googling:

It has a 1994-1997 AR 145 listed right at the top. Yours should be similar. You can also look for guides for after-market cruise control modules.

SVOboy 05-05-2009 10:36 AM

Furthermore, you can try (physically) looking around on the transmission for something like a 3 wired plug going in near the differential. This would likely be a VSS.

Welcome to ecomodder!

anthonye81 05-06-2009 08:22 AM

Thank you guys! I will attack the dash this weekend and see what I can find/irreversibly damage.

I will also look around for a wiring diagram and post it up, it can't do any harm. However my Googling abilities are nowhere near as good as Mr Socket's...

dcb 05-06-2009 09:02 AM

I think there is a haynes manual for your car too (library? Ebay?) and the local alfa dealer should know where to find a speed signal if there is one.

doviatt 05-28-2009 12:50 PM

How about the same question "Finding the elusive VSS" on a '89 Geo Metro?
This should be easy. Every one has done this to their Metros right?
The info I find id's a yellow/green wire under dash near fuse box. My Haynes manual says this is rear defrost relay.:confused:
Haynes manual has no detail about ECM, only general harness and wire info schematics.

wyatt 05-28-2009 04:26 PM

I found my car's wiring diagram after MUCH searching online. It was in a manual for my car. It had a wiring diagram for the ECU (Engine Control Unit, the computer) and showed where the VSS, INJ, and many others were. I got under the dash, pulled the wiring harnesses off, and... they weren't the same as in the manual! I wound up jacking up the front drivers side tire and measuring ohms between each of the wires and ground while turning my tire. It worked, it was the green and yellow wire and the second to last one tried. You know it's the vss because the ohms will go from 0 to infinity and back several times during a revolution. I found the injector by comparing the color of the wires at the injector to those near the ECU and tapping into the injector from under the dash. My 12v came from the fuse box (though I think I may switch it to from the battery since I can't use my high beams with it) and my ground is just grounded to the chassis. I would guess I searched for the wiring diagram for several hours, and actually doing it with the method above took about an hour.

EDIT: I should add, the injector has two wires running to it, with the key on (not engine running) unplug the injector and measure both wires, one is 12v the other is 0v, tap the 0v one. Mine was yellow, maybe with a black stripe.
Also, I think these methods are covered in post #1 of the MPGuino page.

doviatt 05-28-2009 04:45 PM


Thanks for the info.
I've already got a good injector signal I used with my recent tach install.
I'll give it a try with the wheel spinning thing for VSS.
When I measured my green with yellow stripe wire with the engine on, it had 14 volts. That doesn't sound like what I'm looking for. Must be a different color on the '89?
Seems like I've read looking behind instrument panel for where spedo cable plugs in. Does this sound reasonable also?
Thanks, I'll start digging

Edit: my first sentence is unclear and just plain wrong. I used ignition coil -gnd for tach install but found the injector signal on the TB where it should be for the MPGuino hook up.

wyatt 05-28-2009 04:58 PM

I think you could find it that way, but for me at least it was faster to use my voltmeter to test the wires while turning the wheel since I already had the wiring harness pulled off. I pretty much hope I never have to pull those again... what an unnatural position with my feet in the air, head on the floor, and trying to maneuver my hands up behind the dash... That being said, it really didn't take too long.

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