They say that trouble comes in threes.....

[antijam]

...and the case of my C3 they currently (pun intended) seem to be electrical. First the clock stopped, then the battery isolator isolated at the wrong time, now I've just noticed that the ammeter has ceased to function. I'm not sure quite when this first happened - I don't normally give the ammeter much attention. I guess it could be a side effect of my fiddling about to sort out the first two problems. Whatever the cause, it needs sorting. Before accessing the meter I did check that the alternator was actually charging, which it is, but with no deflection of the meter. Putting the lights on and sounding the horn produces no negative deflection either.
So, it's off with the passenger side lower dash panel (again!) which gives me access to the back of the ammeter. The meter is wired with a two-pole connector, one wire being black, the other black/white. I remove the connector and check continuity between the two spade terminals on the meter. It's open circuit so the meter is duff. While I'm there I check voltage at the plug; there's 12V on the black lead but 0V on the black white. There should be almost identical voltage, at around 12V on both, so something else is wrong too.

The ammeter wiring circuit is shown by this diagram...
The supplies to the ammeter are protected by fusible links. Since I'm seeing 12V on the 'B' wire that part of the circuit must be sound. Since there's no voltage on the 'B/W' wire I'm inferring that the fusible link in that part of the circuit has failed. The diagram indicates that the fusible link is situated in the wiring between the bulkhead connector and the horn relay connections. I don't know what the fusible link looks like and so far checking the wiring in the engine bay has not shown anything obvious. I'm wondering if I'm looking for just a single length of wire or whether the link is actually some sort of module perhaps? Can anyone help me identify it and if so, how is it replaced?
I have a new meter coming from the States but in the meantime everything else in the car seems to work so I'll carry on driving until it arrives. To replace the ammeter the whole centre instrument cluster has to come out (yet again!) and that's not a job i'm looking forward to, but before attempting the replacement I do need to sort out the supply to the meter.

(Would'nt be any fun if it was easy, would it?)

 

[Oneball]

The fusible link is a piece of wire spliced into the loom. They’ve got two round plastic tubes at the splice I think. You replace with another length of the correctly rated fusible link wire.

 

[teamzr1]

The design of the fusible link is that its wire is 4 awg sizes smaller than the wiring to which it is attached.

This means that when a dead-short occurs, the [smaller] fusible link wire will 'fry' instead of the regular wiring to which it is attached. Further, the fusible link wire is sheathed in a non-flammable material (so that IT cannot catch fire) and the terminal ends are inert so that they cannot catch fire nor become hot when the fusible link melts.

There needs to be four fusible links:
1 at the starter solenoid (14 AWG brown = 80 Amp?)
1 at the horn relay (16 AWG Black = 60 Amp?)
2 at each end of the ammeter wire (20 AWG orange = 40 Amp)

That fits as with the wiring drawing you show as the 2 fuse links a the AMP meter

Wiper Relay



Starter

 

[antijam]

Thank you guys - at least I know what I'm looking for now. Some PO of my car went liberally round the engine bay with a black rattle can - all the engine bay wiring is a uniform matt black, which doesn't make identification easy. Most of it does seem to come off with some hard thumbnail action, so I'll be busy for a while!

 

[teamzr1]

As mentioned, fuse link is sheathed in a non-flammable material so would look and feel different
and is smaller gage size

 

[Custom exotics]

If you have uprated your alternator to one that can output more than the ammeter gauge is capable of handling then bypassing that gauge might be more appropriate

 

[antijam]

Thanks to the advice on what to look for I finally locate the appropriate fusible link. It's sheathed with orange fire-resistant insulation which I strip off to expose the wires. Sure enough its broken, so to verify that it's the full cause of my problem I solder the two ends back together.....



...and recheck the voltage on the ammeter plug. Now have 12V on both poles of the plug so I now know my problem. Question is, what to do about it. Fusible link wire is very rare over here but still available in the States. To import a short length is going to cost around $40 which seems expensive. Only source I can find in the UK is Claremont. Tom has a reel from which he'll sell a foot for £20. Problem is the cross sectional area identifies it as 14 AWG and I need 20 AWG. There's no point in replacing the link with the same gauge wire as that of the circuit it's trying to protect, so what other options do I have? Seems that a common alternative is to replace the link with an inline fuse but I'd need to work out the appropriate current rating to do this. While pondering this I'm still idly wandering the web and all of a sudden come across this. A guy in the UK has a reel of 20 gauge fusible link wire and sells a 20 cm length for £6. Seems to be the answer and I place my order.

So, once this wire and my new ammeter arrive I've got the happy task of stripping out the centre instrument console again to regain a working ammeter. In the meantime I'll carry on driving. We have the annual village car show next month where my other cars ( MG and Daimler) have both won their classes for the last two years....



To stop me showing them again the organisers have made me a judge this year, so I'm going to turn up in the 'Vette...

 

[teamzr1]

A Question I would have is what caused a 20 amp fuse link to melt ?
What caused that much of a current draw ?
Possible some wire has degraded and went to ground or like starter pulling high load

Yes I agree you have to go with the correct wire gauge and unless you know the cause that link could blow again
so best is to get enough length, so you have spare fuse link if needed

 

[antijam]

A Question I would have is what caused a 20 amp fuse link to melt ?
What caused that much of a current draw ?

If I'm honest 'Team' I think it was probably my own fault for fiddling around the back of the instrument panel trying to fix the clock without isolating the battery first. I'm old enough to know better but I quite possibly caused an inadvertent short unplugging live connections and letting them come into contact with a ground. Anyway, from now on I'm not doing any more electrical work without first isolating the battery. ( I really do not want to strip down the instrument panels again!)

 

[Roscobbc]

Horror stories are known about mechanic working close to a car battery in the engine compartment........wearing a metal bracelet or watch with metal strap.......I can recall many years ago dropping a ring spanner in the engine bay, it falling across the battery terminals and 'firing' back out again at a high rate of knots...... fortunately missing everyone!

 

[teamzr1]

If I'm honest 'Team' I think it was probably my own fault for fiddling around the back of the instrument panel trying to fix the clock without isolating the battery first. I'm old enough to know better but I quite possibly caused an inadvertent short unplugging live connections and letting them come into contact with a ground. Anyway, from now on I'm not doing any more electrical work without first isolating the battery. ( I really do not want to strip down the instrument panels again!)

OK, that makes sense
You should be fine than in just replacing that fuse link