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Bandit
Original Poster
1,505 posts
149 months
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Has anyone had any experience with the dashboard wiring? My Cerb has developed a fault whereby the rev counter / tachometer has stopped working. I've noticed the car no longer puts on any miles either. I'm assuming the wire has just become loose, as the other day when I went over a rather large pot hole the thing started working again (but only until the car was switched off). First question - I'm assuming the two things are connected. Can anyone just confirm that the tachometer drive the mileage clock (its digital in my Cerb)or is there going to be more than one wire loose. Secondly, How easy a job is it for me to try and fix? I have the wiring diagram but had not actually taken a look yet. Is the wiring easy enough to get to? Would this require soldering or is it just a physical connector that needs reattaching? Can a rank novice fix this sort of thing? Note: it took me the best part of a morning to change the battery  Thanks for any advice!
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Tanguero
3,302 posts
70 months
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Bandit said: Can a rank novice fix this sort of thing? Maybe. Bandit said: Note: it took me the best part of a morning to change the battery Ummm, make that probably not!  There are numerous plugs and connectors behind the dashboard and the dash its self is a PCB attached to the fascia. In theory its easy enough to take the nacelle off - 2 wing nuts up under the scuttle panel, but it can be a bit of a game getting the wiring out without unintentionally disconnecting something. There is so much behind the dash its fairly unlikely that anything loose will be obvious. If you problem can be cured by fiddling with every connector you can find then yes you can fix it. If its more complicated than that, who knows. Can you read and understand a wiring diagram and do you have a meter and an oscilloscope?
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Bandit
Original Poster
1,505 posts
149 months
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Tanguero said: Can you read and understand a wiring diagram and do you have a meter and an oscilloscope? I'll take it to the garage 
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pmessling
1,109 posts
72 months
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Shot me if i'm wrong, but have i not read that the big fuse can cause the speedo/rev counter to do funny things?
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Tanguero
3,302 posts
70 months
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It certainly can do, but the usual symptom is erratic bouncing up and down rather than just not working. The big fuse is only in the charging circuit, so rev counter symptoms are presumably a result of marginal voltage to the ECU I guess.  If the odometer has stopped reading as well as the rev counter I think there might be two separate issues unless it is an electronic one.
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aide
670 posts
33 months
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If it's a loose connection you could perhaps start buy spraying behind the dash and the ECU connector with contact cleanAnd then a dab of ContralubeCan do this for the rad fan theromostat connector as well as the throttle pot connectors etc etc..
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Bandit
Original Poster
1,505 posts
149 months
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Tanguero said: It certainly can do, but the usual symptom is erratic bouncing up and down rather than just not working. The big fuse is only in the charging circuit, so rev counter symptoms are presumably a result of marginal voltage to the ECU I guess. If the odometer has stopped reading as well as the rev counter I think there might be two separate issues unless it is an electronic one. Before the rev counter stopped working it was a bit erratic (bouncing up and down, not working until i hit about 10mph). My odometer is digital (its a late 2003 Cerb). Could the big fuse be the cause?
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Tanguero
3,302 posts
70 months
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Bandit said: Before the rev counter stopped working it was a bit erratic (bouncing up and down, not working until i hit about 10mph).
My odometer is digital (its a late 2003 Cerb).
Could the big fuse be the cause? Its certainly worth changing it before doing much else.
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ridds
6,540 posts
113 months
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Big Fuse
Speed sensor (on the diff)
Stuck Odo is usually mechanical if it's at *9999 miles. If not then it's purely because you have no speedo pulse.
As for the revs not working I would guess it's a dodgy connection on teh back of the dash or corroded terminals on the output from the ECU. If it were the sensor you'd have some funny engine running also.
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Bandit
Original Poster
1,505 posts
149 months
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ridds said: Big Fuse
Speed sensor (on the diff)
Stuck Odo is usually mechanical if it's at *9999 miles. If not then it's purely because you have no speedo pulse.
As for the revs not working I would guess it's a dodgy connection on teh back of the dash or corroded terminals on the output from the ECU. If it were the sensor you'd have some funny engine running also. Engines running fine. Odo is digital, not mechanical. My initial guess was bad connection on the dash as it suddenly started working againnfor a bit after getting a big jolt after going down a big pot hole.
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Tanguero
3,302 posts
70 months
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The speedo sensor won't affect the rev counter. That is driven from the ECU triggered by the crank sensor pulse.
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Jhonno
734 posts
10 months
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So if it drops out sporadically, it's likely the link from ECU to counter?
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Tanguero
3,302 posts
70 months
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Either that or the big fuse which notoriously causes rev counter strangeness.
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ridds
6,540 posts
113 months
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Bandit said: Engines running fine. Odo is digital, not mechanical.
My initial guess was bad connection on the dash as it suddenly started working againnfor a bit after getting a big jolt after going down a big pot hole. Bahh! Read it as speedo and tacho...  Yeah tacho would be signal from the ECU. Odo, dunno that's a strange one if it's digital. Perhaps as you think a loose connection within the gauge. Perhaps give speedy cables a call and see if they have heard of it before. Does it still display, just not increase?
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Bandit
Original Poster
1,505 posts
149 months
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ridds said: Bahh! Read it as speedo and tacho... Yeah tacho would be signal from the ECU. Odo, dunno that's a strange one if it's digital. Perhaps as you think a loose connection within the gauge. Perhaps give speedy cables a call and see if they have heard of it before. Does it still display, just not increase? Yeah, the odo digital display still shows the mileage... it just hasn't moved on since the tacho stopped working. When the tacho briefly started working again after the pot hole incident, the mileage on the odo started clocking up again which is why I assumed they were linked some way.
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ridds
6,540 posts
113 months
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Would make sense, perhaps it uses the tacho signal as a trigger to say increment mileage to prevent the counter increasing when being towed? Quite why you would need that function I have no idea! Nothing in the drawings here due to it being a change for the later cars.
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Tanguero
3,302 posts
70 months
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I don't think it can use the tacho signal for the odometer - it would have no way of knowing what gear you were in, hence the ratio of road distance to engine revolutions.
Your first guess of a loose connection may well be right and like I said it may well be fixable by unplugging and re-plugging all the connectors behind the dash.
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ridds
6,540 posts
113 months
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Sorry didn't write that very well. Not the trigger itself but perhaps an additional line.
Perhaps the Odometer has to see the wheel speed signal AND a tacho signal for it to increase. Whereas the speedo works with just the speed signal.
I think they have to be linked some how if it started increasing again when the tacho restarted.
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Tanguero
3,302 posts
70 months
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ridds said: Sorry didn't write that very well. Not the trigger itself but perhaps an additional line.
Perhaps the Odometer has to see the wheel speed signal AND a tacho signal for it to increase. Whereas the speedo works with just the speed signal.
I think they have to be linked some how if it started increasing again when the tacho restarted. I see what you mean - yes it certainly sounds like there is a connection of some sort.
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Bandit
Original Poster
1,505 posts
149 months
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Thanks for everyone's thoughts. Given my lack of faith in my mechanical capabilities I'm going to get the car up to the garage to see if they can help. Cheers 
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