Strange little charging issue on a '65 4.2. Initially all fine, charges about half scale on start-up but after approx 5 mins the needle starts flickering back & forth across the meter and ign light flickers with regularity. Ignition light actually remains on all the time despite ammeter showing charge. Any thoughts, anyone ?
Thanks,
Anthony
Worn brushes?..
I agree. And it is an easy fix as they are accessible.
Disconnect the battery first!
Certainly could be brushes, but I suspect the voltage regulator, based on the fact that it acts up after slightly warm. You could try testing the alternator on the car while warm to see if it acts up then, by bypassing the voltage regulator.
Tom
The ignition light on earlier cars is unrelated to the alternator. It’s controlled by an oil pressure switch on the right side of the engine. If the problem is a flickering meter, it may be brushes, or carbon fouling on the commutator. If the problem is an always-on light, it’s the pressure switch.
Is the red ign light as strong as before turning the key to start, or is it about half as intense in colour when driving?
Thanks indeed for the replies, guys.
Michael - yes the light is always on, but I have oil pressure on the gauge so presumably the switch is ok; maybe there should be another wire from it, though ?
Peder, if there’s any difference in the light’s intensity, it’s barely detectable and certainly not half. That said, the light pulses regularly in tune with the flickering ammeter.
We have an agric. engineers a mile or so away, with a guy who’s very good on alternators, starters etc., so he said to take the car along there one day. Today I went out and the flickering didn’t seem as bad (permanent light though), which might point to brushes.
Will keep y’all updated !
Not sure why this reference is here?
Anthony,
You may have misunderstood. The sender for your oil pressure gauge has nothing to do with the oil pressure switch which drives the red “Ignition” lamp on your year of E-Type. They are completely separate independent circuits. If your Ignition light is always on, I would suspect the oil pressure switch (mounted in one of the oil gallery plugs on the RH side of the engine), or the wiring to it. If it is pulsing in time with the ammeter it is probably just reflecting the fact that your alternator output is “alternating” 
. You may find that if you turn on your headlights, they also keep time to the music!
And to emphasize, the light has nothing whatsoever to do with your alternator or ammeter, It isn’t even related to the oil pressure gauge. There’s a separate switch in the oil gallery which drives the light.
Anthony, what did you ever find?
Tom
Belated thanks, David and Michael.
Well, it would seem that I simply don’t have this other switch. I have the regular oil pressure switch C23016 (no. 35 on p 54 of the parts book), and only the one wire on the loom with no spare connectors. And there doesn’t seem to be any other switch mentioned in the parts book. I suppose I always assumed that the light would only come on if the pressure dropped to zero.
The ammeter seems to have settled down a bit now so I’ve left it alone, although I’m not convinced it’s charging much as the lights don’t get brighter against the garage wall when you blip the throttle.
Edit: I stand corrected ! Just had a look under the bonnet - there’s the sensor on top of the oil filter housing which is connected to the gauge, then just to the right of the housing is an extension thingie terminating in a bolt, which should presumably hold the switch C23016 but has never been there all the time I’ve had the car. So I’ll get one of these, although still no sign of any connecting wire in the vicinity…just have to cobble something up. Although if there’s no switch there, it surely cannot be earthing to switch on the light ?
Nothing, Tom ! I’ve just left it alone as it seems to be working ok, although might think twice about a night journey.
Generator output varies at low engine speed but I believe that alternators have fairly consistent voltage at all speeds. In any case a voltmeter is the best way to check.
Yes, you’re right - will put the meter on it, thanks.
I had this exact problem in my car. Drove me batty. Fortunately, I am a systems engineer and decided to slay this one, and at least comfort those who lay awake nights before the ride…