Intermittent battery telltale II

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Intermittent battery telltale II

Postby Vaughnc » Thu 03.10.2019, 00:13

Hi all,
I would like to ask for help with the (red) ignition/battery telltale light. I did ask earlier in the year (May) and received a lot of helpful answers.
HOWEVER I now have some more specific symptoms that I had not noticed at that time. Maybe someone recognises them?

The battery light sometimes - not always - comes on dimly after a short-medium journey.
Normally the light is extinguished after a short stop before setting off again. But today it re-illuminated every time I restarted the car after a few short stops of just a few minutes.

When it starts to glow dimly it will becomes MUCH brighter when I undo the seat belt. At the same time the rev counter jumps by 500rpm. As soon as I reinsert the seat belt the revs drop back to normal and the light dims right down - almost extinguished.

I have had the battery and alternator tested and these are OK. Battery is quite new (old one was simply v old and needed to be replaced).
Alternator charges at 14/14.2v. Alternator belt tension is good. Alternator is relatively new.
Spark leads have been changed twice (original set had degraded, 1st new set had a loose connector that fell off). The latest set seemed to solve the light for a week or two then the problem returned.

It seems to me that something is getting hot after a drive and some electrical property is changing as a consequence. I can't find anything loose.

Is there a possibility of heat affecting the ignition system somewhere, perhaps the coils?
Could it be a wiring issue in the dash instrument panel?

Any help gratefully received as always!
KR, Vaughn
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Re: Intermittent battery telltale II

Postby muley » Thu 03.10.2019, 07:26

Hi Vaughn

Sorry to hear you are still having this problem (sorry, challenge).

I can't help thinking it might be caused by a dodgy earth somewhere ~ you did have one cause a problem with the boost gauge?

Just a thought

Regards

Jim
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Re: Intermittent battery telltale II

Postby Tuga2112 » Thu 03.10.2019, 07:35

Just to clarify.
When you say the revs drop when you put the seat belt.
You mean the needle drops a bit. But the car's engine continues to rev at the same speed, is that right?

My alternator light follows the same behaviour, but it's always fun when the car is running, just a little brighter when the belt is not plugged.

A bad ground could cause that,
Does your car have an aftermarket alarm system installed?
I've noticed from my experience that aftermarket alarms installed in 90s cars usually piggy back into whatever wires are close by. Which cause interesting voltage drop/rises in wires that would otherwise run exclusively at either 0 or alternator output voltage

I know this is not helpful info but may be something worth keeping in mind as you progress your diagnostic.
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Re: Intermittent battery telltale II

Postby Vaughnc » Thu 03.10.2019, 08:13

Thanks Tuga/Muley

Just to clarify - the revs remain constant - it is just that the rev counter needle that jumps 500rpm when I unhook the seatbelt and returns to normal when reconnected. At least I now know that's not a problem unique to my car!

Yes - the car is fitted with an aftermarket alarm. That possibility just had not occurred to me. I will certainly look into this!

A friend who owns a 60's Elan thinks it is an earth problem. I would need to figure out which earth connection is the culprit. No idea where to start with that.

Another slight possibility is I fitted a USB charging point in the dash via the cigarette lighter wiring. I may be clutching at straws here.

The turbo boost gauge problem was probably the wastegate actuator. No problems since tinkering with that AND (I believe this matters) the car has been "properly" used since I bought it. I really think some cars perk up when used regularly with the occasional thrash:) The car had almost no mileage for several years before hand.

Thanks again guys!
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Re: Intermittent battery telltale II

Postby Rambo » Thu 03.10.2019, 08:51

You say the alternator is "relatively new" Vaughan ? I can't remember if I asked you this before, but did it come from ACW Electics in Wimborne by any chance ?

If so, there was a batch or 2 of alternators that were well dodgy in the last 18 months or so :?
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Re: Intermittent battery telltale II

Postby Fredjohn » Thu 03.10.2019, 09:46

If something totally unrelated to an item causes an electrical issue with that item and elsewhere, my experience with fibreglass cars would tell me it is an earth problem.

As a few have already said before me.

I would suggest starting with the electrical manual which shows the wiring diagrams. I think there is also a schematic of all the earth connections, so you can check them one by one.

All the manuals are available HERE

Good luck.
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Re: Intermittent battery telltale II

Postby GeoffSmith » Thu 03.10.2019, 10:06

I would suspect the instrument pack earth which runs via Instrument Pack Harness connector C pin 4 so check the earth (there's a convenient connector for the NA clock behind the SE clock with battery and earth on it) with respect to the battery post.

Actually, you could try pulling the handbrake off and on to see if that has a similar effect to the seatbelt.
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Re: Intermittent battery telltale II

Postby Vaughnc » Thu 03.10.2019, 10:51

The alternator was supplied by ACW. However its been checked by my garage, and I can myself see that it charges perfectly OK. Belt tension is good. The battery is also good - always fully charged. Pretty sure its not the alternator.

The car always starts well and runs fine. All lights of any description work fine (except this telltale).

I will try the handbrake suggestion.
I'll check the instrument pack earth as suggested by Geoff. Sounds most plausible
I may look into the alarm wiring (bloody hard to access!).
I may remove the main instrument cluster altogether and check all connections/bulbs. Why? Because last summer I removed the instruments in order to replace the dial faces with new and replace most of the bulbs (some were not working). I was very careful because the connectors all look fragile.

If its the instrument panel I would expect the issue to be apparent all the time, not after a 20+ minute drive.
Maybe something is rattling loose over time, or is affected due to heat build up (from engine or electrically induced). That points to a dodgy connection and/or earthing.

Finally, the radio seems to uses non-standard wiring connected to the ignition. I recall the radio is supposed to draw power from the speaker/fuse box behind the passenger seat. Power is definitely not coming from there and never has been since I acquired the car. Related or a red herring?

Thanks again to all. I'll update you if/when I have more news.
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Re: Intermittent battery telltale II

Postby Vaughnc » Wed 09.10.2019, 01:00

I think I've solved it. Had a couple of trips with NO sign of the battery telltale light at all!
So what did I do? Two things: (1) replaced the ignition coils with new. (2) checked and cleaned a few nearby earthing points. First was a fine black wire leading to an earth connection adjacent to the ignition coils - on the alu frame that the coils fix to. Second the frame that the coils fit into had some corrosion on the metal surfaces - so I cleaned these. Thirdly the earth strap that links the chassis to the bonnet catch on LH side (i.e. near the ignition coil) had frayed so I tightened the chassis connection, cleaned the strap and added a new connecting strap.
Hopefully this has properly solved the intermittent battery light!
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Re: Intermittent battery telltale II

Postby Tuga2112 » Wed 09.10.2019, 13:07

Vaughnc wrote:I think I've solved it. Had a couple of trips with NO sign of the battery telltale light at all!
So what did I do? Two things: (1) replaced the ignition coils with new. (2) checked and cleaned a few nearby earthing points. First was a fine black wire leading to an earth connection adjacent to the ignition coils - on the alu frame that the coils fix to. Second the frame that the coils fit into had some corrosion on the metal surfaces - so I cleaned these. Thirdly the earth strap that links the chassis to the bonnet catch on LH side (i.e. near the ignition coil) had frayed so I tightened the chassis connection, cleaned the strap and added a new connecting strap.
Hopefully this has properly solved the intermittent battery light!


im glad you got it fixed,
i need to try to clean up the same earth connections you mention. hopefully i can get it resolved.

i always wondered if replacing the bulb with an LED alternative would be a simpler solution. since in reality, if theres a voltage drop between battery and alternator while the alternator works, the bulb would come out dimly. where an LED installed in the correct direction would not give such false positive.
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Re: Intermittent battery telltale II

Postby dapinky » Wed 09.10.2019, 16:11

Tuga2112 wrote:i always wondered if replacing the bulb with an LED alternative would be a simpler solution. since in reality, if theres a voltage drop between battery and alternator while the alternator works, the bulb would come out dimly. where an LED installed in the correct direction would not give such false positive.


Now I might well be talking out of my arse, as I'm no electrician......

...... but I am led to believe that the teltale light wouldn't work CORRECTLY with an LED 'bulb'.

My understanding is that when you first switch on the ignition, there is (may be?) no light iluminated as it requires current to flow the 'other way' - but once the engine is running, it will behave as normal.... but I could be completely wrong :)
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Re: Intermittent battery telltale II

Postby lotusflasherman » Wed 09.10.2019, 17:24

dapinky wrote:
Tuga2112 wrote:i always wondered if replacing the bulb with an LED alternative would be a simpler solution. since in reality, if theres a voltage drop between battery and alternator while the alternator works, the bulb would come out dimly. where an LED installed in the correct direction would not give such false positive.


Now I might well be talking out of my arse, as I'm no electrician......

...... but I am led to believe that the teltale light wouldn't work CORRECTLY with an LED 'bulb'.

My understanding is that when you first switch on the ignition, there is (may be?) no light iluminated as it requires current to flow the 'other way' - but once the engine is running, it will behave as normal.... but I could be completely wrong :)


I would say you are completely right :D
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Re: Intermittent battery telltale II

Postby Saltire » Wed 09.10.2019, 18:11

:agree: I’ve looked at putting an LED in, and I even came up with a ‘cheater’ circuit to make it work normally, but I haven’t got round to building and testing it yet.
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Re: Intermittent battery telltale II

Postby GeoffSmith » Wed 09.10.2019, 19:03

The answer is: It depends. If it's a standard LED it will either work as intended (red) or not work at all (blue) depending on which way it's wired, but if it's an 'ac' LEC (green) then it will just work.

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Re: Intermittent battery telltale II

Postby Tuga2112 » Wed 09.10.2019, 20:24

what i was talking about was what geoff described although i dont know if the red or blue is correct because i cant remember the meaning of the symbol as of regards to the polarity.

anyway my though was. LED only lets current in 1 direction. if the voltage on the side of the alternator is lower than the voltage on the side of the battery, the LED is "on"
when the alternator starts to provide a voltage (usually 14v) its usually higher than the battery (12.4) meaning the LED will be off.

i suspect in my case, the 2v is enough to lightly dim the current bulb. what confuses me is the fact i would assume the battery would be at the same voltage as the alternator because its directly connected to it for the purpose of being charged.

i have no idea if the Green thing is in Geoff's diagram :oops: :oops: :oops:
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Re: Intermittent battery telltale II

Postby GeoffSmith » Wed 09.10.2019, 21:31

When the alternator pushes out ~14V to charge the battery, the battery terminal will rise to the same voltage provided the connection is low resistance. If you have a bad connection then any resistance will cause a voltage drop when battery charging current is flowing causing the charging light to glow so e.g. if you have 0.1 ohms and the battery is being charged at 20A there will be 2V across the warning light. An LED will stop this but you are not fixing the problem that needs fixing - cleaning up the connections between alternator and battery would be my first port of call.

The green thing is a bridge rectifier (4 diodes traditionally used in old school ac-dc supplies) arranged so that current will only flow one way through the LED no matter what polarity is applied.
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Re: Intermittent battery telltale II

Postby lotusflasherman » Wed 09.10.2019, 22:44

Tuga2112 wrote:what i was talking about was what geoff described although i dont know if the red or blue is correct because i cant remember the meaning of the symbol as of regards to the polarity.

Think of the triangle as an arrow pointing in the direction that will pass current and the bar the direction that will block it ... so triangle is anode (+), bar is cathode (-).
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Re: Intermittent battery telltale II

Postby lotusflasherman » Wed 09.10.2019, 23:05

Saltire wrote::agree: I’ve looked at putting an LED in, and I even came up with a ‘cheater’ circuit to make it work normally, but I haven’t got round to building and testing it yet.

Just two LED's in parallel with one reversed will provide a light whichever the polarity. You can get them made like that but I've only seen big ones that wouldn't fit without a lot of mucking about with instrument cluster. Direction Indicator would need one too if you were converting to LED's.
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Re: Intermittent battery telltale II

Postby donsladek » Thu 10.10.2019, 01:13

lotusflasherman wrote:

Just two LED's in parallel with one reversed will provide a light whichever the polarity. You can get them made like that but I've only seen big ones that wouldn't fit without a lot of mucking about with instrument cluster. Direction Indicator would need one too if you were converting to LED's.


I agree! I used two very bright green LEDs and a resistor in a twist base for the dash indicator, so I can see them in sunlight. :cheers:
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