Red ‘L’ dash light does not come on at all.

[Pablo M]

Some part of the charging system isn’t working, for sure. I’ve already ran the battery dead couple times. 
 

Some background:

 

Recently I redid my driver door seal. I did part of it then came back to it days later to finish it. I left door open when I did, not realizing it would leave the interior light on. To be honest, I didn’t even know that worked. Finished seal and went to start it but completely dead-not even a starter click. So far red

light still working. 
Took battery to auto parts store and got it charged. Drove the car around a few times and noticed each start was weaker, until it just wouldn’t turn over. I didn’t notice if the red light was working. 
Took battery to auto parts store and got it charged again. 
Now I’m paranoid about it because the red light doesn’t come on at all at startup. 
 

Weeks ago when I got the 123+ distributor in and got motor running I had constant red light on so I replaced the voltage regulator with new Hell unit, since it was cheap and mine looked original. It was actually that the belt has come loose. 
 

I also recently did some electrical work. Installed a plug and play LED headlight set up. Also added a LED third brake light, wiring it up to the driver taillight. 
Come to think of it, when installing the headlights I did mess with the VR plug. I’ll check that again just in case. 
 

Anything else I should be checking first? 
 

Otherwise really, finally, enjoying the car driving it around. 

['76mintgrün'02]

You could check the L-light bulb to make sure it's not burned out.

 

Have you put a volt meter on it while running, to see if the alternator is charging?

(I usually use my Innova 5568's volt meter).

 

You might want to consider adding a battery charger to your shopping list.  It'd drive me nutz to have to go someplace to charge the battery.

 

 

 

 

[Hans]

How old is the battery?

[Mike Self]

For the alternator/charge bulb not to work at all is unusual (barring a wiring problem or a burned out bulb).  That light has two + (positive) feeds running to it--one from the battery, the other from the alternator.  When the car's not running and you turn the ignition on, the battery's current lights the light; once you start the engine and the alternator is turning fast enough to generate power, it also supplies power to the bulb.  The two + currents cancel each other out, and the bulb goes out.  You may have noticed when you have a heavy current draw (headlights, heater and wipers on simultaneously, for example) the bulb may glow dimly--that means the alternator isn't supplying enough current so the battery's current is causing the bulb to go on.  

 

So...no light means that your battery isn't supplying current to the bulb with the ignition on and the engine off.  First of all, do a load test on the battery.  It may show 12 volts and have no amps at all.  Presuming it's good, start checking the battery terminals and wiring--clean and tight (no bolt on battery terminals).  Then check the ground end of the two battery ground cables--big one to the block, small one to the body.  No ground = no current passing between alternator and battery.  And make sure the external ground wire fastened to the alternator's frame and grounding on the block is intact and not all frayed under the terminals.  

 

Finally, insure the plug at the back of the alternator and the one plugged into the voltage regulator are both nice and snug in their sockets, and there's no corrosion there either...

 

Let us know whatcha find...

 

mike

[conkitchen]

This may not be helpful, however. To quickly check your alt to see if it's putting out the juice. while the engine is running-disconnect the negative ground. If the car stalls your alt is not doing it's job.  

 

As a Sears tire & battery man for a semester, that was the quick trick I was taught. 

 

See tag line below. 

Edited June 23 by conkitchen

[jimk]

12V from the battery side comes from the ignition switch to the hot size if the 3 fuses ganged together in the fuse box.  From the fuse box power goes to the cluster.  Check continuity from the appropriate pin on the cluster to the light socket.

On the other side from the alternator power comes from the regulator to the diagnostic port where it is dual crimped to the appropriate pin on the diagnostic port.  From the diagnostic port the blue wire goes to the instrument cluster thru the 12 pin connector and on to the light.  Check for continuity from the regulator to the instrument cluster main connector pin.

Person doing the diagnostic work should read the wiring diagram for the correct pins.

[Son of Marty]

Make sure the ground wire from the alternator to the block is in good shape.

[John76]

1 hour ago, jimk said:

Person doing the diagnostic work should read the wiring diagram for the correct pins.

Here's a guide that might help.

 

 

 

[OldRoller]

On 6/23/2024 at 9:01 AM, '76mintgrün'02 said:

You might want to consider adding a battery charger to your shopping list.

The best charger I've found in years. Light, easily stored, 25 amp charging, float charging, battery reconditioning, starting juice (says 75 amp but it's more like 60 amps). $50-90 depending on source. 

3 years so far, no issues.

BC25BS | stanley12volt

WWW.STANLEY12VOLT.COM

 

[Pablo M]

Thanks everyone for all the useful and helpful suggestions.

I started the diagnostic process with the bulb. Was good. 

Battery is 3-1/2 years old but checked out at 13v across the terminals with key off.

All the main grounds looked good.

Went to the voltage regulator even though it was new (or because of it) and pulled the plug to check for resistance/continuity and two of the male blades came out with the plug. Cheap Hella VR I had swapped in when I thought it was bad (ended up being belt that came loose). So, I grabbed the old one to connect it back and it worked! The 'L' charge light is working again with the old, original voltage regulator.

 

Problem solved: bad Voltage Regulator

Edited June 26 by Pablo M
added info

[SVK289]

Hello!

My problems also started with a non-working Red light on the dash, on my newly-acquired '74. Then the battery died and I changed it. It died again and I got the alternator rebuilt. Now the Red Light came on - but wouldn't go off until I hit 2,000 RPM. It would come on again if I dropped engine speed to below 2,000. But the voltage would climb to 14.5 with increasing engine speed. Thanks to the help of @Mike Self, I got through all this troubleshooting.

 

Checked all the wires, ground, etc. and then determined it had to be VR. I got a new Echlin VR-503 (after reading several blogs here), and put it in instead of the relatively new Beru VR. Now the voltage is more stable (around 13V at 2,000rpm), drops just a little (0.5V) when I turn the headlights on. However, the Red Light doesn't want to go off. After the engine starts, it is constantly dimly lit. 

Any other Gremlins to go after?

 

BTW, not sure if it is related, but my Oil light doesn't come on at all, with ignition-on. 

[SVK289]

On 6/26/2024 at 12:56 PM, SVK289 said:

Hello!

My problems also started with a non-working Red light on the dash, on my newly-acquired '74. Then the battery died and I changed it. It died again and I got the alternator rebuilt. Now the Red Light came on - but wouldn't go off until I hit 2,000 RPM. It would come on again if I dropped engine speed to below 2,000. But the voltage would climb to 14.5 with increasing engine speed. Thanks to the help of @Mike Self, I got through all this troubleshooting.

 

Checked all the wires, ground, etc. and then determined it had to be VR. I got a new Echlin VR-503 (after reading several blogs here), and put it in instead of the relatively new Beru VR. Now the voltage is more stable (around 13V at 2,000rpm), drops just a little (0.5V) when I turn the headlights on. However, the Red Light doesn't want to go off. After the engine starts, it is constantly dimly lit. 

Any other Gremlins to go after?

 

BTW, not sure if it is related, but my Oil light doesn't come on at all, with ignition-on. 

@John76 Any suggestions?

[OldRoller]

Sounds like an internal alternator issue, likely a leaking diode in the trio keeping just enough juice on the dash light circuit to illuminate the bulb dimly. Pull it and have the rebuilder check it out.

No oil light should not be related. Possibly a loss to ground on the sender wire or a bulb out.

[John76]

5 hours ago, OldRoller said:

Possibly a loss to ground on the sender wire or a bulb out.

+1 on the oil light. 

An easy check is to disconnect the lead on the oil pressure switch and ground it when the ignition is on.

If the light comes on, replace the pressure switch.

If the light does not come on, check the bulb in the dash pod.

 

16 hours ago, SVK289 said:

Now the voltage is more stable (around 13V at 2,000rpm),

Where are you taking the voltage reading? Best place is right at the battery terminals when engine is at 2k rpm.

I used the original Bosch VR but could never get close to 14v at idle speed (900 rpm).

Then I switched to a solid-state VR (Hella) and now idle volts are above 14v. No dim alt. light ... even will all lights and accessories on. If you have a voltmeter on your dash/console, tap into the +12v to the rear window defroster switch and a good ground.

 

 

 

 

 

 

[SVK289]

Thanks, @John76 and @OldRoller. I've been out of the country last few weeks and haven't been able to try out your suggestions. Hopefully this weekend.