TR6 TR6 ignition light faint - this can't be good

[ichthos]

And yet more problems. I have had limited driving time due to constant rain. On my ride tonight I just noticed that the ignition light stays on very faintly. It is so faint that I didn't realize it was on until it got dark out. Is this an alternator problem, and something I should be worried about? How can I narrow this problem down so I know what is wrong? I am hoping to make a road trip this summer and don't want to have to worry about something stalling my trip.
Kevin

 

[tdskip]

Sounds like a case of the alternator fading. Have you checked the volts at the battery when the car is running?

 

[ichthos]

What do you mean by the alternator fading? I haven't checked the battery while the car is running, but it's my bed time. I will check it out tomorrow night and get back. Thanks,
Kevin

 

[Deleted member 8987]

Bed Time?
Oh, yeah, I forgot. Youngsters need their beauty sleep, gotta be in bed by 2100 local.....

 

[tdskip]

Hi Kevin - basically you measure the volts at the battery while the car is running to see if the alternator is keeping it charged.

Assuming that all the connections are tight and everything is connected properly this is a good, and easy, test.

You want to see over 13.5 volts at the battery. Do you have a multimeter handy?

Guys - any better way to explain this?

 

[joejoecat]

Make sure your fan belt is tight.

 

[poolboy]

Since you are also having PDWA problems, I have to ask.
Are you sure it's the red light that you see and not the orange oil pressure light ?
Sorry for asking the obvious, but I don't want to take anything for granted.

 

[TR3driver]

Very faint may not even indicate a problem, only that the alternator is working hard to charge the battery and keep up with the lights, etc.

The light basically compares what the alternator should be producing (sampled by the "diode trio" inside the alternator), to the voltage in the ignition circuit. Normally, with the key on and the alternator spinning, they are both battery voltage and the light goes out. What the light is supposed to indicate is the condition where the alternator isn't working (so the trio output is below battery voltage).

But it can also come on if the alternator output rises higher than the ignition circuit, due to voltage drop in either the charging circuit (between the alternator and battery) or the ignition circuit. A bad main diode (inside the alternator) can also do it.

So, start by verifying that the alternator is working, by checking its output voltage as above. If so, the issue is relatively minor (meaning you can safely drive the car). But if the light still bugs you, start looking for why the alternator voltage is higher than ignition voltage.

 

[DNK]

Kevin, you still running a stock Alt?

 

[ichthos]

I checked the fan belt, and I think it is adjusted correctly. I never am insulted by questions, so yes I'm reporting to you accurately on which light it is. It is the light directly next to the hazard warning light. I will be checking the voltage with the car running when I get home tonight. Yes, the alternator is stock. It is the "it could be" things that bother me before I go on a trip. If the battery is charging at 13.5 for instance, and the light is still on, doesn't there have to be something wrong for that light to be on faintly? I have no idea how to check out the different part on the alternator, Randall. Is this something I need to take in to have checked? I was thinking of taking in my used spare to be assessed anyway.
Kevin

 

[tdskip]

So I don't think we asked when you see the light. If just at low RPM, probably nothing to worry about. If at speed then maybe a bit more of a concern.

Do you have a multimeter handy? Single best way to get a baseline here.

 

[poolboy]

"It is the light directly next to the hazard warning light."

Ok Kevin, but do you mean the red jewel like lamp in the bottom of the tachometer ? One is oil pressure the other is ignition.

 

[lbcs_r_fun]

I had a problem like this on another car, not a TR. The problem was that one of the six diodes was bad. This limited the amount of charge so the light began to flicker and eventually was bright! I replaced the alternator which solved the problem.

T

 

[DNK]

If it was a "B". I would say that was normal.
Let's fix this TR

 

[lbcs_r_fun]

No, not a B, a VW, actually, but it doesn't matter. The Lucas alternators, like most others use a 3-phase, full-wave bridge rectifier with six diodes. If one or more of these diodes fail, the alternator continues to operate but at a reduced rate and can not carry all of the electrical load plus charge the battery. So, as a result, the battery voltage eventually drops below the alternator and at that point the red light begins to shine. The rectifier assembly can be replaced, which is a simple straight forward job. The TR6 repair (Bentley) manual provides some simple tests to determine if the alternator is OK.

So, regardless of the brand of car the alternator <span style="font-weight: bold"><span style="text-decoration: underline">may be the cause. </span></span>

 

[TR3driver]

So, regardless of the brand of car the alternator <span style="font-weight: bold"><span style="text-decoration: underline">may be the cause. </span></span>

That was exactly what I meant by "A bad main diode (inside the alternator) can also do it."

Kevin, my suggestion remains the same: get yourself a (cheap) DMM, learn to use it, do some basic troubleshooting yourself. But if that is more than you can handle, then Yes, take it to a shop and have it checked out. They won't necessarily help with the light glowing faintly, but they can quickly check out whether the alternator is working correctly.

Don't know if they still do, but Sears used to do that check for free. O'Reillys checked my battery for free, so they might do a free charging check as well. Or any shop shouldn't charge more than $30 or so; it's a quick and easy test with the proper equipment.

I don't know all the variations of TR6, but I thought some years had the ignition warning on the dash rather than in the speedo. In either case, it may be possible to see light from some other source that appears to be the ignition lamp. Mine (on the TR3) lights up with the turn signal flashers (because light from the turn indicator bulb shines onto the back of the ignition lamp).

PS, these meters are so cheap, they are basically disposable. IMO every LBC owner should have at least one or two.
https://www.harborfreight.com/7-function-digital-multimeter-90899.html

 

[ichthos]

Went out to test my battery, but found my cheap meter is bad. I will have to pick up another before I can see how things are charging. When I started the car this night, the ignition light came on and stayed on. I noticed that once I raise the RPM even slightly it goes off and stays off. Is this normal? I have owned this car for about five years now. I could never get the RPMs below 1,100 all that time. After some recent work I now have the idle down to 850. So does this sound normal? I am still going to read through my Bentley and get a new meter so I can test my spare and see how my battery is charging this weekend.
Kevin

 

[Deleted member 8987]

Pretty normal to stay off until the RPM's come up, then stay off.....

Sometimes you will find low idle can give a glowing lamp.....

 

[TR3driver]

He meant stay on until the rpm comes up. I agree, not unusual at all.

 

[tdskip]

He meant stay on until the rpm comes up. I agree, not unusual at all.

+3, in other words everything is probably fine. So rather than working through all the potential options let's get a good multimeter on there while the car is running at 1000 RPM and confirm you've got 13.5+ volts.

$5 says you do and all is well Kevin.