Red Light stays on when I start

[Richard Sjolund]

I started my 1964 C coupe yesterday and the red generator light lit up - and it stays on. The fan belt is turning and the generator brushes look OK. The generator is fairly new and has been charging for less than 5,000 miles since it was installed.

Where should I start? I have a meter and I can check voltages -- but where?

Richard Sjolund
Solon, (Iowa City), Iowa
1964 (September 1963 build) 356 C Karmann Coupe (Ruby Red, color:6402)
On the 356 Registry cover- November, 2005; July, 2018

[WilliamVaughan]

Measure voltage from Generator body terminal D+ (armature output) to case of generator body (D-) with engine RPM at approximately 2500 to 3500 RPM (exact RPM value not important).

Voltage ought to be more than battery voltage. It ought to be 7.2 volts.

(I think your car just wanted more attention.)

[Bill Lawless]

Measure the Battery Voltage when car is not running, then when running.. Should be 1/2 to 1 or some voltage higher when running, this will tell you if the generator is working.
Are the brushes sliding up/down freely?

[Doug McDonnell]

Also check tension on your belt. If slipping it could cause your problem.

[Richard Sjolund]

OK--- The voltage from D+ to D- is about 4 volts. I have a spare voltage regulator and I swapped that - no change, red light stays on.

My generator is from Zims - less than 3 years ago. It is their "Premium Remanufactured" unit .... I had some help to install it in Amarillo, Texas - Thanks to Mike Horton who came to rescue me. I wrote an article about the TAN - Travel Assistance Network - and how it got help for me.

Now I need to replace the replacement --- With core charge and shipping it will be a big hit on this month's car budget ....

My old generator lasted for over 20 years - and it only died because I failed to check the brushes ...

I wrote about that, too:

viewtopic.php?f=1&t=41602#p264733

At least I can get the car to Stalltek for service - 30 miles on the battery is no problem.

[Geoff Fleming]

Another test for a dead or low-output generator, is to loosen the ground strap at the battery, rev the engine to 2,500rpm with the car stationary. Have someone hold that engine speed or use a weight on the throttle to keep it there. Now, with engine revving, lift the ground away from the battery. If the engine dies immediately, the gen. is probably the culprit. If, however, the engine continues to run, it is receiving voltage from the generator and the problem lies with the regulator.
If you have the older, black box regulator, you can remove the cover, ( shut the engine/ignition off for this), you will see three poles with 'fingers' of thin metal on top. Carefully use a piece of paper to slip between the contact points of these fingers. Sometimes one will have stuck and cause the red light to appear. Always worth a try. Replace cover securely before re-starting the engine.

[Richard Sjolund]

Thanks for the tip - - I swapped the voltage regulator with no effect on the red light ....

Richard

[Thomas Sottile]

You can cook a generator if you regulator is the small c type by over loading the generator such as headlights draw gps and phone only the large reg has real protection I have cooked two almost new generators until iswitchto the large black one

[Dave Wildrick]

You can cook a generator if you regulator is the small c type by over loading the generator such as headlights draw gps and phone only the large reg has real protection I have cooked two almost new generators until iswitchto the large black one

My friend, Jim Learmonth, lost 3 generators to this effect of the small silver 6V regulator before Joe Leoni set him straight. The silver regulator cannot be set to a limited number of amps, and when the generator's demand greatly exceeds 23 amps (like wanting 40 or more), the regulator will let that amount pass--resulting in the generator throwing solder from the armature and destroying itself. I replaced the original small silver regulator on my 65C coupe with the big black one about 5 years ago. My 64C coupe came with the big black one--so no worries.

Shifting subjects, a few years ago I had a newly rebuilt generator fail after driving only 75 miles. The red light stayed on as on Richard Sjolund's car. It turned out that the rebuilder had run a wire slightly too short to one of the posts inside the generator. The soldered joint failed from vibration and the wire fell off the post.

[Tim Berardelli]

Gotta ask, Does the light go off when you release the handbrake?

[Geoff Fleming]

Tim...Excellent! You never know, could be something as simple as mistaking that light for the other red one on a C car's gauge.

[Harlan Halsey]

Richard, there are two brushes, the bottom one is quite difficult to access, Each is pushed into contact by a flat coil spring. if either of those springs breaks, the red light goes on. An easy check of the generator is to remove the fan belt, disconnect the connections to the regulator, and connect a battery or battery charger, minus to ground, D-, and plus to D+, Jumper DF to ground. The generator will then run as a motor, drawing about 9 amps. (I once saw a mechanic do that to run the fan, cooling the heads enough to do a valve adjustment!) If it doesn't run the gen is bad. If it runs the reg is bad.
BTW when all is well, you can check the gen/reg system by measuring the voltage between any ground and B+. At idle V=6v. As you slowly speed up the engine, the B+ voltage will rise until limited to 7.2v at about 2500 RPM. Note that all this is easy to do from the engine compartment. Also, you should periodically move all ground connections: battery, chassis, transmission.
Good Luck

[Martin Bruechle]

Used to take sandpaper on a popsicle stick to cleap up a armature (while running), new brushes, sometimes put 12v from the coil to get them going.

[Richard Sjolund]

"Thomas Sottile wrote: Thu May 30, 2019 2:51 pm
You can cook a generator if you regulator is the small c type by over loading the generator such as headlights draw gps and phone only the large reg has real protection I have cooked two almost new generators until I switched to the large black one."

OK. I have a new 6 volt generator on order - and a new black box regulator, too. My pair of small silver regulators will go to the trash.

My car has the the SMD headlights, and LED rear lights. It should be a low amperage draw. I do have a pair of 6v to 12v converters, and I power my GPS and my cell phone on the road.

I have the 6V Optima gel battery - and I'm having my new Black Box regulator setup for that combination.

I'm eager to get Ruby back on the road ....

[WilliamVaughan]

The next voltage test is similar to previous.

The difference is, this time short the DF terminal of the Generator (field control point) to the D- terminal (the body of the generator). With engine at approximately 3000 RPM, the generator should put out more than 7 volts. If it does, then the problem is likely in the regulator.

(Your car's problem could be a dirty contact in the voltage sensing relay of your regulator. )