92 GQ TD42 - Tacho not working

[Ricardo00]

I recently purchased a 91 (not a 92) LWB GQ and the tacho wasn't working when I purchased it so I don't have any info around how/when it stopped functioning.

Today a mechanic friend did some work on it and I asked him to have a quick look at the tacho. He reported back that he "wiggled" some of the leads coming off the alternator and it seemed to start working and was working when he dropped it off however I just moved it out of the driveway this afternoon and the tacho moved briefly when I first started it but then nothing after that.

My mates no auto sparky so I figured I should do some research my self.

I understand some of these have a tacho operated from a sensor and others run from the alternator, can I test the output? how do identify which one I have?

Are there any common causes for the tacho to not work?

I imagine the best way to identify the cause is by a process of elimination, what tests can I do? (I have a multimeter)

Thanks in advance :)

[97_gq_lwb]

Might be easier to get someone in the car watching the tacho whilst you wiggle the wires and connectors around the alternator and visually check them.
Mine has a sensor on the front of the engine for the tacho.
Heres a pic of a blanking plate where my tacho sensor is
http://www.dustinmcmurray.com/wp-content/uploads/2012/01/blanking-plate.jpg

[Ricardo00]

So I went for a short drive today, when first started truck Tacho wasn't working then started working when driving up the road, stopped briefly at the lights then started going when I drove off so it appears I currently have an intermittent issue.

Had a look in what I believe is the same location 97_gq_lwb has shown above (below thermostat housing, to left of the alternator and to the right of water pump) and it looks like I have a similar plate however with a pair of cables coming out of it. Should the tacho sensor be sitting behind this or am I looking in the wrong place?

[97_gq_lwb]

that is your tacho sensor yes

[Ricardo00]

Thanks, should I presume the sensor is ok since the Tacho works intermittently?

[97_gq_lwb]

I would think so more likely a bad connection or a wire shorting maybe even dry solder joints on the tacho itself unplug it at the joiner and check it for bad connections.

I can't be 100 % but i think one side is earthed from memory and the other you can get a slight reading of some sort on khz on the multimeter.
With the engine running ofcourse lol.

[Ricardo00]

Sweet thanks, I'll check all the connections I can find and go from there.