View Full Version : Help! Battery Not Recharging!

06-12-2008, 10:44 AM
I recently completed the restoration of my 62 TR4, which included the installation of a new wiring harness, battery, and voltage regulator. I also cleaned up the generator and installed new brushes. With the battery fully charged, the car fires right up and runs all day, and there's no drain on the battery while the car is running or sitting. However, each time I start the car, it depletes the battery's power a little bit until it won't work anymore (lasts about 10 starts or so). Jumping the car will get the car running, but with no consequence to the battery (it won't recharge). Once depleted I have to hook it up to my trickle charge, after which its good for another 10 or so starts. Additionally, the ignition light doesn't come on when you turn the key, but rather will glow randomly while driving sometimes (usually when the battery is running a bit low).

So, with a new voltage regulator installed (I also tried using the previously working original as well) and a presumably functional generator (I haven't checked it, but the car runs fine so I presume its working), and a functional ignition light system (the bulb isn't burned out at least), does anyone have any ideas as to what's going on? Do I need to re-polarize the system to negative ground (already was before I installed the new harness and regulator)? If so, does anyone have instructions for how to do this without burning out my brand new harness? Do I need to go back through my wiring and check for mistakes? Could the generator be the problem? Greatly appreciate your thoughts.


06-12-2008, 10:56 AM
Polarity: It's a good practice to repolarize the generator whenever it's been disconnected from the system.

You might have a mis-wiring issue, but I sure can't see it from here. Recheck everything.

"...and a presumably functional generator (I haven't checked it, but the car runs fine so I presume its working)"
The car is running fine on the battery. The gen could be stone dead and you would be getting exactly the symptoms you are describing -- except the red light should be glowing. Definitely, check the generator.

Andrew Mace
06-12-2008, 11:44 AM

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Additionally, the ignition light doesn't come on when you turn the key, but rather will glow randomly while driving sometimes (usually when the battery is running a bit low).[/QUOTE]Yes, something definitely is wrong; the IGN light should glow brightly when the key is turned on and, with a generator, "extinguish" once the engine is running. Depending on various factors, it might glow ever so faintly at idle, especially if there is a significant load (i.e. headlights on), but that's it.

06-12-2008, 12:39 PM
Repolarizing is not the problem; but could certainly be a wiring mistake or (more likely IMO) an intermittant connection somewhere.

I would focus first on the light not working with the engine stopped, just because it's the easiest to troubleshoot and hopefully will lead you to the problem.

Get a voltmeter of some sort (a cheap DMM from HF works just fine) and connect the appropriate lead to a good ground (ie negative lead if the car has been converted to negative ground; positive lead if you are running the original positive ground). Preferably get the ground right at the battery, then meter to the other battery post just to be sure it's making contact. Radio Shack sells some inexpensive "test jumpers" with alligator clips at each end that are very handy for this kind of testing (I always carry a couple in the car along with a cheap DMM).

Then with the key on, touch the other meter lead to the 'D' terminal on the control box. This should show no voltage (or only a few millivolts). If you find voltage here, either the generator is completely toast or it's not grounded properly. Check again to the generator case and to the big terminal on the generator to identify that problem. Could also be that the control box is shorted or the cutout contacts are stuck closed, but that's unlikely IMO.

If 'D' has zero volts as it should, then the light is not working properly. Time to fish it's bulb holder out of the lamp and check the voltage right at the bulb holder. The brown/yellow wire from the control box should still show 0 volts; if not there is a problem with the wire or where it's connected (should be to the 'D' terminal on the control box that you already checked). The white wire should have 12 volts on it; if not there is a break in the wire or a bad connection where it joins the other white wire at the ignition switch. If one has 12v and the other 0v and the light isn't on, then the bulb is bad (could be intermittant) or (more likely) not making good contact with the bulb holder. If the light came on as you fished it out, likely it's the bulb not making good contact.

That ought to get you started, write back with the results and we'll go to the next step.

06-12-2008, 03:13 PM
Thank you all for the input. I think its unlikely that the generator is stone dead since the battery shows no depletion between starts and I've driven the car 20 plus miles (to work) many many times without incident, so long as I keep the car running. Additionally, I can jump the car with the battery completely dead and then drive it for 30 minutes without incident.

Still, the generator could perhaps be putting out a diminished level of juice, enough to run the car but not enough click over the regulator and charge the battery... Hmm...

I'll check and recheck the wiring and run the recommended tests and let you know how I fare.

Just in case, can anybody provide precise instructions on how to polarize the system?


06-12-2008, 05:34 PM
If the battery has sat unused for a length of time, it could be sulfated. A heavily sulfated battery will take a charge, but not to it's full capacity. Small trickle chargers will indicate a full charge, but it is not.

If you have a hydrometer I would bet it will show a low charge.

If your charger has the ability to charge at a set rate rather then the normal taper, hook it to the battery and over charge for 6 hours. Periodically check the water level. This is called an equalization process and will force the sulfates back into solution.

Saved many a "bad" battery this way.

06-12-2008, 06:21 PM
The first LBC I worked on was an MGB with a charging system fault. We could drive that car for days on end without recharging the battery. Don't be fooled into thinking the generator is working just because you can drive the car 20 miles and start it 10 times. If the battery is in good order you can drive a long time without a functioning generator or alternator.

Take Randall's advice and start by figuring out why the charge warning lamp is not coming on with the key. Progress through the system from there.

06-12-2008, 06:23 PM
Speaking as one who has done exactly that (because my generator was toast and I had to earn a paycheck to replace it); it's quite possible to get 10 trips to/from work on a good battery with no generator action at all, if you don't run the headlights, etc.

If the generator is working at all, then it doesn't need to be polarized. The polarization (aka residual magnetism) is only important when you first start the engine; and gets refreshed as soon as the cutout contacts close (connecting the generator to the rest of the electrical system).

But one way to polarize it is to remove the wire from the F terminal on the control box, and touch it to the A terminal. Only needs a moment, so no need for a permanent connection. You may get a small spark, don't worry about it.

Another method, the one generally given in the books, is to momentarily connect a jumper from D (or F) to A (or A1, or the hot post on the battery). But you'll get more sparks that way and it overloads the armature and brown/yellow wires (which is why it's important that the connection be made for only a moment).

IMO a badly sulfated battery wouldn't even start the car once, so I doubt that's the problem.

06-12-2008, 06:31 PM
A $10 multimeter and a helper (to rev the engine slightly) will quickly confirm whether the generator is putting out enough juice. I, like others above, suspect you'll find it's not... You can go a long way just on battery with these cars, particularly if you don't do a lot of night driving!

06-12-2008, 08:07 PM
To a fellow New Englander, welcome to the Forum.

Get that car running well and soon. We have a lot of British car club activities up here in th summer.

06-13-2008, 05:48 PM
I had the same issue, ign light and all, that lasted for about a month or so before my starter just stopped working one day. No problems after the new starter was installed. I have no idea whether the two were actually related, or just dumb luck, but maybe a shoddy starter is draining more of your battery than it normally should each start?

06-22-2008, 09:30 AM
Thanks for everybody's previous advice. I'm embarassed to say that the ignition light problem was a simple connection under the dash that came loose. I re-did the connection and, sure enough, the light came on...

And stayed on. As with all these things, solving one problem leads to the discovery of another. I recharged the battery fully and ran the car for a while, but the light did not extinguish. The battery doesn't seem to be depleting as it did before (though I can't really tell because I haven't run it very much since the 'fix'), but does anybody know why the light would stay on?


PS, Anybody in the Boston area can give me this advice in person at British Car Day at Larz Anderson Park next Sunday. I have the blue surrey top TR4.

06-22-2008, 10:02 AM
The light indicates that the output voltage of the generator is never coming up to battery voltage (which normally should happen in the first second or two after the engine starts).

Could be either the generator or the control box is at fault. Or both, as control box problems can kill the generator.

First check the obvious, like the fan belt is tight (I had a lot of trouble with the front lower generator mount coming loose) and the wires from the generator to control box are securely attached at both ends, not cracked or broken (especially near the exhaust manifold).

Then try polarizing the generator, as above.

If still no joy, try removing the generator wires from the control box (terminals D and F) and temporarily jumpering them together. Also connect a voltmeter from the junction to ground. Start the engine and keep an eye on the voltmeter as you rev it just a little bit (1500 rpm). According to Lucas, 0 volts indicates a problem with the brushed or armature (could also be an open wire to the generator). 2-4 volts indicates a problem with the field circuit, either an open coil or again an open wire. 15 volts or more indicates the generator is working (meaning the problem is in the control box). (BTW, try not to let the voltage go over 20 volts, as that can damage an otherwise working generator.)

I've got a PDF copy of the Lucas testing instructions; PM me your email addy if you'd like a copy. About 2Mb. Someone has it up on a web site, but I forget who offhand.