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Discussion Starter #1
I went through the site and read every speedo question I could find and nothing like this comes up.
Speedometer and Odometer do not work - they did a while back - maybe 2 years ago (the car has not seen 1000 miles in 4 years). Tachometer is working fine.
I went to the pulse generator today and disconnected the cable - I cannot turn the cable with my fingers so it is firmly in the transmission. The blades are cruddy on the connector - I will clean them with dielectric grease tomorrow. My question is - what should the readings be across the blades? Using an ohmmeter what should I be looking at? If the pulse generator comes up bad - and I know they are somewhat rare - how much are they and who has them? I have looked and no one seems to have them in stock.
What should me readings be back into the car? I have not pulled the speedometer yet.
I am going to start into this tomorrow - tired and mechanical have never gone together well.
Any help would be appreciated.
 

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You can find them popping up on eBay sometimes, here's one. You can also find them NOS from Centerline or from Highwood Alfa, not sure if that one is NOS or what. Before you consider replacing the pulse generator make sure all connections are clean, I go a step further and replace connectors when they are worn rather than cleaning them (especially if original to the car). Often a bad connection will look completely fine but in reality be too worn to function.

I have little experience working on Alfas beyond S2 so I can't be further assistance debugging the one you have. I would wait for others to chime in with test procedure before jumping the gun on replacing yours. Have you verified the speedo cable turns when the car moves? Perhaps it feels firm because it has seized in the transfer tube, if that's the case it may need to be replaced. Definitely make sure the drive cable is functioning.
 

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As I have a NOS spare Pulse Generator (PG) to hand, I went to the garage and did some tests

The 3 pin connector from PG
pin 1 is ground wire (black)
pin 2 is 12v power wire from fuse #7 (white, or can also be pink-black)
pin 3 is the signal output wire to the speedo instrument (grey)
Pulse generator plug.jpg

you cannot test anything without the PG being powered up.
here are my tests results with it on the bench:

you need a battery source and a drill with something that fits the speedo input drive hole. A vise to hold the PG steady is useful.
I used a small Motorcycle battery that was not fully charged, showing only about 7V

I clipped a lead from battery positive to pin 2
and from battery negative to pin 1
then with my DVM set to 20 kOhms (kilo ohms), I clipped the DVM leads to pin 3 and to pin 1 (doubling up with the battery negative lead)
then I spun the drill on slowest speed

result: fluctuates but output was around 10-12 k Ohm..
now I know that is not very scientific, but good enough to show the PG is putting out a signal
(imo, these things are either working or not)

In another post I mentioned voltage output between 0,2V and 7,08V that I read on a spanish forum, but I could get no reading in volts mode, either DC or AC...so I am going to edit/correct that.
 

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Discussion Starter #4
SteveSpiderGuy - Thank you very much- I took a very small jewelers' file and cleaned the contacts and then hit them with cleaner. When I put them back together I used dielectric grease - to no avail. I am going to put the car on the ramp the check the cable just to be sure.
 

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Discussion Starter #5
SpiderSerie4 - Thank you very much - I am going to bench test the PG later on today. The figures give me something to work with to at least know if I am getting a signal out of the generator. It is scientific enough for what I am trying to do.
 
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