Headlights causing GEN light?

[PA69Z]

Hello, anytime I turn on my headlights its causes my GEN dummy light to come on in my 69 z28 302 v8 4spd, its original, (things ive tried) I just replace the battery, alternator, and voltage regulator with a delco remi, not the wells 715. The alt is charging fine 14.2v at 2k rpm and then hold there. I been running through the connections to check for lost ground or corroded connections, no smoking guns yet. The headlights work fine both high and low, I'm not popping fuses, I just never saw the gen light come on when the alt and vr are charging fine. Any help would be greatly appreciated.
Thanks, Shawn

[tom]

Is the problem at idle only, or also at speed? Most alternators don't put out much power at low RPM's.

[PA69Z]

Any rpm, if the headlights are on the gen light is as well regardless of speed no other lighting does it (turn signals, brakes lights, interior lights). I suppose there has to be something wrong with the headlight circuit.

[1968RSZ28]

Any rpm, if the headlights are on the gen light is as well regardless of speed no other lighting does it (turn signals, brakes lights, interior lights). I suppose there has to be something wrong with the headlight circuit.

Not necessarily.  I had the same thing happen on my Chevy truck.  I removed and opened up the alternator and found the brushes completely worn out.  I replaced the brush set along with some other small parts = problem solved!  

Paul

[PA69Z]

Interesting, not sure thats it, the problem has persisted over multiple alternators, voltage regulators and batteries (all were replace trying to solve this issue, the VR is the only thing that was actually bad). However I will have to add it to my check list, thanks for the input.

[Everett#2390]

Check the brown wire circuitry.
From the ign sw, there is a brown/white wire to firewall connector, approx. 30 ohms resistance for the length.
You will have to remove the GEN bulb to measure as the GEN bulb is a parallel path, with bulb in place, you will measure bulb resistance, a lower value than the single wire.
Next measure the brown wire from the VR to the firewall, or better yet, the light socket on one side as it should be less than one ohm.

When ign on, engine off, one side of GEN bulb has ign power, the other side/contact is lower value, hence a glowing GEN bulb.
Engine running, VR brown supplies power from VR relay of equal amount of power and GEN bulb goes out.
If there is a difference of voltage in the two powers provided, GEN bulb dimly glows.
With a warm battery, VR cover temp of approx. 130°F, battery voltage should approximately be 13.8 volts, no accessories on, VR may be adjusted alittle high.

[ban617]

 What about your grounds ? Bad grounds will pull alot of amps/voltage also...

[hotrod68]

   I'd suspect the printed circuit as well. I had maddening problems on my '68 with the idiot lights, as well as the turn signals and dash lights. One little short in the printed circuit and it can all go haywire. To add to it, sometimes you can't SEE the short. It looks perfectly normal with no burned places or obvious flaws. Good luck.

[jethog737]

I just purchased my 1969 X77D80 Z/28. When my headlights are on they ever so slightly go bright then dim, bright, then dim. Like every half second they alternate. This occurs at any rpm of the engine. I did notice this morning that behind the engine on the drivers side is a "ground strap" that is hanging from the firewall and not connected to anything. It is a fairly good size strap. Could this be a possible cause? Not enough engine ground? Thanks for your input....  Jeff

[Rick68]

It sounds like the circuit breaker is coming off and on.If that is the case then you have to find out where the short is on that circuit.

[ss jim]

Jethog737, the ground strap end should be under a valve cover hold down bolt. My car had the pulsating headlamps and the voltage regulator was the problem. Jim