Tacho Rpm Gauge Gremlins

[rikky 37]

My 205 GTi6 is all standard, and running the soldered tacho mod (photo below showing it). When I switched the car on and start it up, the gauge fires all the way round to maximum RPM before finally settling in the correct place, and works as you would expect. So, not really troubling too much as it works fine until first switched on.

 

What I have noticed is that when I switch the sidelights on (with the car running), and then the hazard light or indicators, I get the fluctuation between the revs in the interval between the indicator flashes. So it'll be sat nicely at 1000rpm, then I switch on the sidelights and indicators, and it'll flick fom 1000rpm to 2000rpm, back to 1000rpm, up to 2000rpm, etc, until you switch the indicators off.

 

I'm guessing something fundamentally broke up or damaged on the clocks, so took them out, and noticed the circuit board has had a repair and has an earth spade soldered on. But surely the earth isn't earthing the full strip of printed circuit, it's only the part closest to one end, as there's a break?

 

Going to try some conductive pen/paint stuff on it and redraw between the break first of all as I don't think solder will stick there.

 

So, anyone any ideas or ..? I read on here someone else having the tacho sweep issue on first fire-up but can't find it now. Hmph!

 

Photos:

 

 

[Anthony 1,003]

The symptoms do sound earth related to me so I'd look into that first. If you unplug the rest of the instrument cluster so only the tacho is plugged in, does it still misbehave when other electrics are switched on?

[rikky 37]

The symptoms do sound earth related to me so I'd look into that first. If you unplug the rest of the instrument cluster so only the tacho is plugged in, does it still misbehave when other electrics are switched on?

 

Just tried everything unplugged except the blue 3-pin plug behind the tacho, and the symptoms remain. It fires up fine etc and settles at 1000rpm, but hazards on or other electrics means the RPM goes up and down.

 

The wire repair in my photo above is because the green third-from-end wire on the blue second plug to the clocks is snapped, so that's been joined directly via a spade terminal. But that doesn't look related to the issue.

 

Not sure where to start to look now though!

 

For the blue plug with the broken wire, I found this:

 

C (blue):

1. Battery/charging warning light [7A]

2. STOP light (connected to A4)

3. Handbrake/brake fluid level warning light [70]

4. See A5

5. Direction indicator light, left [37A]

6. Parking light indicator [55R]

7. Dipped beam indicator [R1]

 

But a few of my pins in the plug aren't there.

Edited October 5, 2016 by rikky

[rikky 37]

My broken wire which is bodged back together is in fact the number 3 (Handbrake/brake fluid level warning light, wire no 70)

 

All earths seem ok too..

Edited October 5, 2016 by rikky

[rikky 37]

I've read literally every thread on this subject and can't really find what my issue is likely to be other than a dodgy earth, but have tried manually earthing the clocks again at the tacho plug but its the same. So can only assume it's picking a strange signal up from the loom or there's a tacho clock fault.

 

Should I try a new tacho? Have chopped my existing solder mod through the wire to revert it back to being dead (i.e. how you'd expect it to be with the GTi6 conversion).

 

Should I try a different tacho mod method, e.g. the 4-wire / coil method? I had one off Mei but appear to have got rid thinking I'd never need it

 

I've tried the method of bypassing the boad by linking the yellow wire to the top left pin but this seems to give the same results

 

Anyone?

[Chipboy 0]

Check earths, this could be signal cross talk or fluctuating earth loop.

 

The earth you are interested in is part of the tacho signal, ideally it should be a shielded cable, the old green 205 one is such a cable, this wires back towards the ECU and earths on body at ECU earth point, stopping earth loops.

 

I am about to do this too. the signal then has to be acceptable to the Tacho, this is another subject altogther,

[Chipboy 0]

Also check the 12V supply to the Tacho, it should be stable and if it fluctuates with load then there is your issue, this is possible too.

[rikky 37]

Thanks for the input, will be giving it another look over at some point. Have looked at the FAQ on the wiring for the instrument cluster here - http://www.205gtidrivers.com/articles/m-instrumentpanel.html - but looks to miss a few pins out and also my clocks only have 3 of the 4 pins present (seems common). So should I assume it's 12v, earth, and signal? I've checked all my earths as best as I can really. All the earths on both headlight corners, main earth, gearbox earth, steering column earth, rear left light earth..

 

I guess I could bypas the loom and run a length of wire to the tacho signal direct from the GTi6 loom to the clocks to test that?

 

Like I said it behaves until you turn sidelights, hazards, or any power draw on.

 

I'll get a multimeter on it tomorrow

[rikky 37]

You mention the green earth is part of the tacho signal - is this on the 205 loom then, and if so, where? From the plug forwards? My wire in the 205 side of the loom (112) is blue and goes right to the tacho. I do have a spare redundant wire, think it's 112B or 112C (Yellow) at the back of the tacho but it goes nowhere and seems to be fairly common.

 

With the 3 tacho pins, I have manually earthed it, give it a constant 12v live, and wired it direct to the speedo wire from the GTi6 and it's exactly the same.

 

Can you elaborate on the bit about the earth that's part of the tacho signal? What's this, and where is it?

 

Surely if it's got power, earth, and a decent signal direct from the GTi6 ECU, with the solder mod, it should work? I think normally people just run the coil tacho mod thing direct to the Wire # 112 and that's it (no solder). I'm thinking the solder mod or something on my tacho isn't working (even though I re-did it) or the tacho itself is damaged

Edited October 12, 2016 by rikky

[petert 588]

The outer shield on the green cable is earth. Thus the three pins on the tacho are signal, earth and +12V. I don't think the tacho has anything to do with the cluster. If you've made changes, then possibly you have no earth.

[rikky 37]

I have took the tacho out of the cluster entirely so it's just the tacho in my hand with no other instrument cluster plugs connected to anything, and like I said above I hard-wired the earth and +12v, and connected the signal pin to the signal wire on the GTi6 loom - with the same results. (this is with the solder mod as per your thread - so yellow wire here it passes into the board, bridged to the top left solder joint) - Revs work fine, stable, and accurate until you switch anything on like hazards or flash the driving lamps, and then it fluctuates (but re-settles back to where it should be)

 

Not following 100% on the green outer shield bit.. are you saying that the remnants of the ECU side (which is all the GTi6 bits, joined to the 205 brown plug) could have the earth wire in there which has potentially been soldered badly or wrongly to something? To be honest I've been really careful with the wiring side of things, most wires went like for like to the right numbers, everything else works perfectly, gauges and all, and I triple checked it all before soldering anything. The only thing I noticed was some things were in different physical positions in the plugs to the wiring diagrams in the guide here but it's all gone together smoothly really.

 

I'm thinking I damaged the tacho soldering the bridge wire onto it but I'd have thought I would have no signal whatsoever if that was the case?

 

For an electrical novice, what would your course of action be if you were me?

Edited October 12, 2016 by rikky

[Chipboy 0]

Highly unlikely to have damaged the tacho, unless its very dry and a static zap did somehting. Soldering irons are gerneally earthed. The outer shieath is a shield that forms a coaxial cable designed to reduce interference to signal wires, it should be earthed at one point / end. So it should not connect at the tacho to anyhting bu at or near the connection tot he GTI6 loom it should be earthed as is the ECU? I have to do this too so I will lok at your references and see if I can get my tacho registering at all!

 

Given the problem occurs when a load is switced on it likley to be power related not shielding the only exception to this is induced interference bit this is only a remote possibility. By power elated I mean both positive supply and the earths, this is typical signal type issues and you just need to persevere.

[rikky 37]

To put this to rest..

 

Picked up a Spoox tacho adapter off someone local on here the other day, fitted today and works perfect, so consider this solved