Non-working Or Intermittent Tacho, R33

[JimX]

I typed this up into the DIY forum, but it seems to have disappeared or needs to be approved or something. So in case it's gone into the void or it doesn't quality, I've copied it into here as well.

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I had an intermittent tacho, which gradually declined into a full non-working tacho for the past month or so. After finally getting the time to rip the cluster out again and doing what I described below, the tacho started working straight away. I'm not 100% sure this is what fixed it but I'm fairly confident it has. This procedure may apply to different cars with similar setups, just check the correct pins and plugs etc. It's fairly straightforward.

Diagnosis:

What I found is the metal tag on the black loom plug that goes into the tacho (the lower one on the side with 2 plugs on it, the right side as you look forwards) was sitting a bit lower than the other 2 on either side of it. Since this plugs into a socket which has a stiff plastic sheet for holding the connectors, I imagine that the 2 higher tags were lifting the sheet up and out of the way to make the contact with the tacho signal wire dodgy at best, and depending on how the car flexes and moves as you drive, possibly breaking all contact.

Procedure:

1. Remove the instrument cluster (not covered in this DIY, should be somewhere else in this forum)

2. Find the plug that goes into the tacho. On mine (R33 GTR) it's the lower plug on the right side looking forwards.

3. Find the tacho signal wire pin/tag on the loom plug. On mine, it's the pin that goes into something labelled "TAM" in the cluster socket, which is a track that goes directly into a bolt that holds the tacho on. The signal pin on mine sits between 2 other metal tags in the only group of 3 tags on the black plug.

4. Clean the metal tags and the copper track contacts with some electrical contact cleaner, plus maybe rub clean with something non-abrasive.

5. With a pair of jeweler's screwdrivers or similar (safety pins should be fine), very gently prise up the metal tag on either side of the middle, where the bend in the metal is, to make it flush with the 2 on either side of it. Try to keep the pressure uniform on both sides to avoid over stressing the metal.

6. Plug the dash back in and test it before reassembling everything, to make sure it works, or that you haven't made things worse.

7. If it's all now working, reassemble everything and have a celebrationary beer for having saved yourself a couple of hundred for a new tacho/dash cluster.

7a. If it's still not working, at least now you have ruled your loom/plug as a problem, and can more easily send your dash out for repair or replace it with another one.

One more amateur diagnosis check:

When I had everything apart, I checked the resistance on the tacho signal wire for the hell of it. The resistance went quickly from some high value to open circuit, each time I tested it and swapped to the earth next to it and back again. Since my tacho now works, I imagine this reading is indicative of a properly working tacho signal wire. If you have an earth here instead, or it doesn't skip from high resistance to open circuit, or some uniform low resistance value, then you might have a problem with your signal wire. I'm not an expert here, so this is just speculation and something for you to try while it's all apart.

NOTE: DON'T DO THIS WITH THE IGNITION ON!!! I always check voltages before resistance, to make sure I'm not buzzing out a 12V live feed.