Charge Light Wiring Issue

[Jeff Troy]

Hi, Friends,

I know that I'm often the one passing out the advice, but I am having a really strange problem that has me - and the local German VW air-cooled professional - completely baffled.

My GT has been on (and occasionally off) the road for more than 44 years. The charging system has always worked, but since the last rebuild I finished a week go, it doesn't seem to be doing it correctly.

Previously, I would start the engine and the warning light bulb (exciter) would light and then go out, as it should, telling me that the charging system is working properly. Now, the bulb is on whenever the car is running and does not go out, and I don't know if the charging system is working -- but I think it's probably not.

I have always used the generator warning light, and my personal notes show a RED (+) wire from my instrument-panel-mounted bulb to 4A on the main fuse block, and a BLUE (-) wire from the bulb to the alternator (I use the alternator with the internal voltage regulator).

Bulb is good. Wires are good, not frayed or damaged in any way. Alternator is good, and we also connected a new one just to be sure (same results). No blown fuses, All seems to be in order.

The Bradley GT Wiring Manual makes no reference to the warning light, so I looked at thesamba.com and saw that the warning light in a Beetle should be powered by the BLACK/YELLOW wire from the VW steering column. There is also something in the GTII manual about what MAY be the warning light, but it isn't clear. The GT manual shows the BLACK/YELLOW wire in a dotted line going to the Bradley harness's RED wire to fuse 1A, which is tied by a jumper to fuse 3A. The manual shows another dotted line connecting the RED Bradley harness wire to the GREEN harness wire going to +L on the amp gauge. As far as I know, that circuit is always hot, even when the car is at rest.

My car has the RED and GREEN Bradley harness wires connected, but I can't remember if the BLACK/YELLOW wire is also connected there. The engine starts and runs fine as always, but the charge light and possible charging issue truly have me puzzled.

If one of you VW wiring gurus uses the exciter bulb, would you please tell me how it should be hooked up? My panel mounted bulb does not ground at the base; it has a (+) pole (RED wire) and a (-) pole (BLUE wire). The BLUE ground is not an issue; it goes to the correct terminal on the alternator.

My questions, in the shorter form, are:

1. Where should the RED (+) wire from the bulb be connected,

2. Should the BLACK/YELLOW wire from the VW column be connected to the GREEN and RED Bradley harness wire as the GT wiring manual suggests with its dotted lines, and

3. If the exciter bulb is connected to an always hot circuit, it must be the voltage regulator that takes it out when the charging system kicks in, so why wouldn't my bulb now behave as it always has, instead of always remaining lit?

Bottom line... HOW IN THE F DO I HOOK THIS THING UP?

Thanks in advance, and warmest regards,

[Gary Hammond]

Hi Jeff,

1. Where should the RED (+) wire from the bulb be connected,

I don't have a wiring diagram and my ignition switch is on the dash instead of the steering column. But the red (+) wire from the bulb needs to be connected to a positive voltage source that's always on only when the ignition switch is on.

Now, the bulb is on whenever the car is running and does not go out, and I don't know if the charging system is working -- but I think it's probably not.

You mentioned that your ammeter is still hooked up. What does your ammeter show? If it's charging, the ammeter will tell you this. If it's showing constant discharge, then the alternator is not putting out current to the battery and load. That means only the battery is carrying the load.

3. If the exciter bulb is connected to an always hot circuit, it must be the voltage regulator that takes it out when the charging system kicks in, so why wouldn't my bulb now behave as it always has, instead of always remaining lit?

If your blue wire is accidentally shorted to ground somewhere the light will stay on and the alternator will not put out current.

Gary Hammond,

[Jeff Troy]

Hi, Gary,

Thanks, bud. I'll check that.

Please email me ([e-mail]) with your mailing address.

Warmest regards...

[jspbtown]

Hey Jeff....Exciter wiring is easy.

So...two wires to any bulb right? One positive and one negative source. One wire comes from a keyed ignition source. It should provide + current when the key is in the "on" position. It can really come from anywhere.

Now to light the bulb you need a - source. That comes from the Alternator/Generator. That wire comes from the D+ terminal on the alternator (integral regulator).

So....when the car is turned on (but not running) the bulb gets + from the keyed source. And it gets the - from the grounded alternator. When you start the car and rev the engine (you must rev the engine to about 2000 rpm) this "excites" the alternator coil and the - signal is overcome by the + signal and the light goes out as it now has two + signals and no ground.

Sounds like some wire chasing is in your future. I would start at the bulb. The wire that supplies the ground is likely the culprit or the alternator is messed up.

[Jeff Troy]

Thanks, guys,

During the recent rebuild, I rigged a second exciter in the engine compartment (perhaps as a courtesy to some unknown VW mechanic?). I disconnected this today (Saturday) and retraced the remaining wires.

The hot wire from the remaining dash-mounted bulb goes to fuse 2B on the main block: that circuit is hot only when when the key is on. The negative wire from the bulb goes to the small + (D+) on the alternator. The light comes on when the key is on accessory and when the starter engages. Unfortunately, after the engine started, the light remained on.

I let the engine idle for a few moments to see if the bulb would go out, and I revved the engine a bit to give it a reason. Still, the light remained on.

I tried this only once, and may not have revved as high as 2000, so maybe it will work correctly when I try again tomorrow (Sunday).

If it doesn't work, the problem could be in the alternator. I'll let you know as soon as I know.

THANK YOU BOTH AGAIN for your help. This is a really silly thing to be plagued by after 44 years and hundreds of thousands of miles on this car. It's almost embarrassing. I know every piece of my Bradley inside and out. It's crazy that something so basic that has always worked has now become so troublesome.

[Jeff Troy]

Hi, Jeff and Gary,

Thank you both again.

Jeff, your explanation of WHY the ground wire from the bulb goes to a hot terminal was significant.

Turns out that yesterday's rewire was correct. I tried it again today, this time revving to roughly 2200 and the light went out.

Just to sure, I shut it down, waited a moment, and turned the key to on; light on. Started the engine; light on. Revved up; light out. Perfect!

Two more cycles confirmed. All good.

THANK YOU BOTH, my friends.

[Gary Hammond]

Hi Jeff,

The circuit thru the light bulb gives the initial amount of current to energize the field coils in the alternator. The more current thru the bulb, the lower the RPM at which the output becomes self sustaining at a voltage a little above the battery voltage. If you change the warning light bulb to one that is a little higher wattage (more current), it will require a lower RPM to energize the alternator.

You didn't replace the incandescent bulb with an LED bulb by any chance did you?

Gary Hammond,

[Jeff Troy]

Hi, Gary,

No. It's a generic, one-piece lamp from one of the auto houses of the day, maybe 1979 0r '80 during one of the early restorations. Bulb is not replaceable; it's a bulb, case, and terminals all as a single component.

They may have been around, but I had never seen an LED piece back then.

Warmest...