Unexpected surprise

[Mr B]

Evening all,

Thought I would share this, at the weekend I changed out the Tacho in my 3 litre Capri as I suspected it was misbehaving, anyway whilst I had the cluster out of the car I cleaned up the Tacho connections (3 small threaded poles) I also cleaned up the small washers and nuts that secure the Tacho to the printed circuit as well as giving the main multiplug connection's a light sanding - very light sanding as it doesn't take a lot to damage the copper contacts, but something unexpected has come out this, I had the usual dim ignition/alternator light problem when braking and signalling - this is now completely gone, I can't remember the last time I had a Capri which didn't have this problem.

I should also add that I cleaned up the voltage regulator connections as well.

Anyone got any ideas how doing the above has cured the dim ignition light problem?

Wayne

[stevemarl]

The Ign light comes on when the engine is off because: one side is connected to the battery +ive, the other is earthed straight through the (inactive) alternator, so the bulb lights. When the engine starts, tha alternator generates a voltage so instead of having a live at one side and earth at the other, both sides of the bulb are at roughly 12v so no current flows. I say roughly beecause any wiring, joints, load on the system will affect this voltage balance and small currents will flow, either way, causing faint glowing. You`re cleaning up of connections has just reduced some of the dry/oxidised joints which has removed some of the resistances and consequent voltage drops.
It`s like the instrument voltage regulator, if the contacts from the reg. unit to the main flexible circuit affair get a bit oxidised, you will get a small resistance between the earth terminal of the unit and the circuit it plugs into. As the current for the gauges may be a couple of amps, a small resistance here will cause maybe a volt or so `drop` between unit earth and actual earth. But the 7805 chip on the unit regulates the positive supply and will still continure to give 5.0v acrosss ITS (the chip`s)output pins. This though is effectively added to the 1v drop between the pin and actual earth, so the actual voltage measured at, say, the temp. sender will read 6/6.5v and thwe instruments will read slightly high, yet the regiulator is working perfectly and just needs the contacts cleaning .

(Before anyone corrects me , yes I know it`s more like 14v when running...)

[pbar]

The Ign light comes on when the engine is off because: one side is connected to the battery +ive, the other is earthed straight through the (inactive) alternator, so the bulb lights. When the engine starts, tha alternator generates a voltage so instead of having a live at one side and earth at the other, both sides of the bulb are at roughly 12v so no current flows.

And how clever is that, really the design of such things makes me wonder just how on earth humans can develop such stuff.

[stevemarl]

Paul,
And it is so,so simple, no computer required! o

[pbar]

Paul,
And it is so,so simple, no computer required! o

Very true yes, and is a high tech all computer state of the art modern car any more impressive? To be honest, not really, no!

[Mc Tool]

I dunno so much , just saying to a mate yesterday about our Toyota Blade. We have done just over 130,000km and I have changed oil and filter at less than every 10k, one new air filter ,one serpentine belt ,changed the trans fluid and filter twice, and I took the plugs out......and put them back in (after checking that the gaps hadn't opened up thus retarding my timing ) apart from fuel and tires, that's it. Covering the same distance in crapi would see me , tweaking the carb, checking the timing ,and setting the valve clearance at least 13 times. In an outright drag race the Blade leaves crapi choklng on its lean burn exhaust fumes ,and it goes round corners better and averages 14.6 km/l, I mean I still rather drive crapi ( they are like rocking horse shit here ) but .......

[Mr B]

The Ign light comes on when the engine is off because: one side is connected to the battery +ive, the other is earthed straight through the (inactive) alternator, so the bulb lights. When the engine starts, tha alternator generates a voltage so instead of having a live at one side and earth at the other, both sides of the bulb are at roughly 12v so no current flows. I say roughly beecause any wiring, joints, load on the system will affect this voltage balance and small currents will flow, either way, causing faint glowing. You`re cleaning up of connections has just reduced some of the dry/oxidised joints which has removed some of the resistances and consequent voltage drops.
It`s like the instrument voltage regulator, if the contacts from the reg. unit to the main flexible circuit affair get a bit oxidised, you will get a small resistance between the earth terminal of the unit and the circuit it plugs into. As the current for the gauges may be a couple of amps, a small resistance here will cause maybe a volt or so `drop` between unit earth and actual earth. But the 7805 chip on the unit regulates the positive supply and will still continure to give 5.0v acrosss ITS (the chip`s)output pins. This though is effectively added to the 1v drop between the pin and actual earth, so the actual voltage measured at, say, the temp. sender will read 6/6.5v and thwe instruments will read slightly high, yet the regiulator is working perfectly and just needs the contacts cleaning .

(Before anyone corrects me , yes I know it`s more like 14v when running...)

Thanks for this Steve, I could have sworn I read somewhere that the rear light clusters were the most lightly culprits in causing the dim glowing ignition light, is that information not correct mate?

Wayne

[Mc Tool]

Poor earth connections can cause all sorts of problems. It's well worth the effort to disconnect , clean and refit the various earths, specially instrument or light clusters . Clean em up with wire brush and Emery paper , there are various potions applicable to prevent corrosion.

[pbar]

I dunno so much , just saying to a mate yesterday about our Toyota Blade. We have done just over 130,000km and I have changed oil and filter at less than every 10k, one new air filter ,one serpentine belt ,changed the trans fluid and filter twice, and I took the plugs out......and put them back in (after checking that the gaps hadn't opened up thus retarding my timing ) apart from fuel and tires, that's it. Covering the same distance in crapi would see me , tweaking the carb, checking the timing....

I see your point, totally. But it's so flamin boring though. And micro chips and computer this and techno that just doesn't get the blood pumping. When I take a carb apart I am constantly impressed by the linkages, mechanics, springs, diaphragms and everything else that humans somehow devised to make this work.

I went for a drive in my Capri last night as I frequently do, all year round, and I just love it.

You are quite right though, the technology of the time coupled with the fact that these are aging vehicles necessitates constant and frequent messing, fixing and tinkering. But I guess you have to take that as part of the hobby and take it in your stride rather than see it is a negative, much like young Danny on here does, he's a credit to that mindset.

Just my take on it of course

[D366Y]

But I guess you have to take that as part of the hobby and take it in your stride rather than see it is a negative, much like young Danny on here does, he's a credit to that mindset.

Very kind words Paul, thank you!
It's not always the most fun having to work outside in the rain but if it needs fixing it needs doing, regardless of the weather

[pbar]

Very kind words Paul, thank you!
It's not always the most fun having to work outside in the rain but if it needs fixing it needs doing, regardless of the weather

You're a credit to the forum.

[stevemarl]

I read somewhere that the rear light clusters were the most lightly culprits in causing the dim glowing ignition light, is that information not correct mate?

Wayne,
I mean, nothings`s impossible, but I`d say that was pretty high up the list. Rear lights can cause all sorts of problems, as mentioned, due to bad earths. Electrickery will always find the shortest path to earth. If one light has a bad earth it may find another easier way to earth is through the filament of another bulb, hence brakes coming on with indicators etc etc. But that would be confined to that cluster: the Ign light is only earthed through the field coils of the alternator., so no, it`s not really possible.
Steve

[stevemarl]

D366Y wrote: ↑
Wed Dec 18, 2019 8:40 am

Very kind words Paul, thank you!
It's not always the most fun having to work outside in the rain but if it needs fixing it needs doing, regardless of the weather

You're a credit to the forum.

I agree!

[stevemarl]

coupled with the fact that these are aging vehicles necessitates constant and frequent messing,

Paul,
You know my thoughts on this, but I think that`s the key fact - they are now all really very, very old in car terms (the average life expectancy when I last read it was still only 12-13 years - so they are on their 3rd lives!) Waterways and rads have decades of corrosion and sediment, oilways full of sludge; parts are often worn, new `aftermarket` parts are of inferior quality (condensers?).THAT is why people need to keep an eye on, it seems, everything. There were no more vehicles on the hard shoulder in the `80s than today, driving in the rush hour was not as you might expect a matter of weaving your way through between the broken down Cortinas, it was just like today (except `rush hour` didn`t start at 3pm). I just feel the technology gets a lot of unfair criticism because it is now, for the most part on its last legs. In 40 years I only had to get the AA out twice, for a blown head gasket and a failed alternator (ironically I didn`t realise the Ign light hadn`t been coming on...)both on the Viva, the Capri did 39k in 3 years, day in day out (and that includes -10c starts at 4am) without a single issue. To do that with,as Paul says, brass jets and bits of springs is actually amazing!

[D366Y]

You're a credit to the forum.

I agree!

Thank you both!

[Mr B]

I read somewhere that the rear light clusters were the most lightly culprits in causing the dim glowing ignition light, is that information not correct mate?

Wayne,
I mean, nothings`s impossible, but I`d say that was pretty high up the list. Rear lights can cause all sorts of problems, as mentioned, due to bad earths. Electrickery will always find the shortest path to earth. If one light has a bad earth it may find another easier way to earth is through the filament of another bulb, hence brakes coming on with indicators etc etc. But that would be confined to that cluster: the Ign light is only earthed through the field coils of the alternator., so no, it`s not really possible.
Steve

Thanks for your replies on this Steve, your knowledge on this subject is exemplary, trouble is I'm now tempted to take the clusters out of my car's now and clean up all the connections!

Wayne

[pbar]

coupled with the fact that these are aging vehicles necessitates constant and frequent messing,

Paul,
You know my thoughts on this, but I think that`s the key fact - they are now all really very, very old in car terms (the average life expectancy when I last read it was still only 12-13 years - so they are on their 3rd lives!) Waterways and rads have decades of corrosion and sediment, oilways full of sludge; parts are often worn, new `aftermarket` parts are of inferior quality (condensers?).THAT is why people need to keep an eye on, it seems, everything. There were no more vehicles on the hard shoulder in the `80s than today, driving in the rush hour was not as you might expect a matter of weaving your way through between the broken down Cortinas, it was just like today (except `rush hour` didn`t start at 3pm). I just feel the technology gets a lot of unfair criticism because it is now, for the most part on its last legs. In 40 years I only had to get the AA out twice, for a blown head gasket and a failed alternator (ironically I didn`t realise the Ign light hadn`t been coming on...)both on the Viva, the Capri did 39k in 3 years, day in day out (and that includes -10c starts at 4am) without a single issue. To do that with,as Paul says, brass jets and bits of springs is actually amazing!

Good thoughts Steve, and you know what constantly amazes me, I frequently drive mine as you know, and I went for a spin last night, as you say these are old aging cars, classic cars obviously. But thirty years later there is still no messing about, no waiting, you fire it up and off you go, like it's a three week old car, not thirty odd years, driving alongside brand new modern cars, on modern roads, in the cold, in the dark, warm happy and having fun. It's incredible.

[Mc Tool]

My brother has just bought a brand new MX5 limited edition......he always reminds me he is 1st in line should I sell crapi ( he's not ) and I wouldn't swap his Mazda for it. It was modern cars that got me off motorbikes.....stereo , heater, seats , cruise control , but they are a bit blaa. Round here
(NZ) I see more Ferrari's ,Lambo's, McLarens and Aston's ( Porches don't even count ) than Capri's. I am considering getting a T shirt printed to read " No , you don't see many of these " coz that's what just about everyone sez when they see it