Headlight Power Draw Level?

[rb1971]

My project is almost completely sorted out now, and I'm down to only a few minor issues.

One of them relates to the headlights. Although I rarely drive at night or in conditions where the lights would be required, when I turn them on I get a significant voltage reduction (down to about 9-10), whereas even with every other electric item on (stereo, heated seats, etc.) I am usually at 12-13. The only other item that appears to have this dramatic of an effect are the turn signals, but of course that is intermittent and short-term so I worry about it less.

Haven't had a problem yet where the car wouldn't start, but I was wondering whether this is normal operation, seems like a possible issue (ground, short, etc.), or something else.

Thanks in advance as always for any thoughts.

 

[Stevehose]

Could be bad grounds, old wires with high resistance, corroded bulb connections or a combo of all. Did you add a relay to the low beam circuit? This makes a big difference.

My project is almost completely sorted out now, and I'm down to only a few minor issues.

One of them relates to the headlights. Although I rarely drive at night or in conditions where the lights would be required, when I turn them on I get a significant voltage reduction (down to about 9-10), whereas even with every other electric item on (stereo, heated seats, etc.) I am usually at 12-13. The only other item that appears to have this dramatic of an effect are the turn signals, but of course that is intermittent and short-term so I worry about it less.

Haven't had a problem yet where the car wouldn't start, but I was wondering whether this is normal operation, seems like a possible issue (ground, short, etc.), or something else.

Thanks in advance as always for any thoughts.

 

[Arde]

Is the voltage reported measured at the battery or at the load point?

 

[jmackro]

Is the voltage reported measured at the battery or at the load point?

Good question.

And a second question is: If you are measuring the voltage at the battery, is this with the engine (and alternator) running?

Without a more detailed description of what you mean by "I get a significant voltage reduction (down to about 9-10)" it is pretty hard to give you a meaningful response.

 

[rb1971]

Good question.

And a second question is: If you are measuring the voltage at the battery, is this with the engine (and alternator) running?

Without a more detailed description of what you mean by "I get a significant voltage reduction (down to about 9-10)" it is pretty hard to give you a meaningful response.

With engine and alternator running, measured by the VDO voltmeter installed in place of the speaker grille (which I am pretty sure reads off the battery). In fact, the same thing happens if I am running down the highway at 70mph and 2500RPM and turn the low beams on - to the point where the car slightly "lurches" due to the load increase. (Presumably this is not normal operation.)

I don't think it's bad wiring generally since the whole harness was rewound and the light switch was replaced, but it could be that the bulb holders are corroded (although they looked clean when installed).

 

[61porsche]

Resistance

equals heat. Find the part that's hot. On lights- switches and the emergency flasher. I bet Fritz at the factory made sure it was working once. It's a false belief to throw a relay at it without solving the first issue. It will bite you sometime when you least expect it.( On the road to Vintage...)

It should be on everyone's list for a long sitting car to sytematically go through and clean connections. 40 plus years is a long time to expect that there's not going to be some issues. I always start with new fuses and tightening the fuse block/ grounds.

Now, off I go to fix that stupid radio lead.

 

[adawil2002]

Clean all electrical connections and grounds, could be as simple as a dirty ground or loose ground at the load shedding relay. The lights, turn signals and coil share a ground at the passenger side near the turn signal.

Put a voltmeter on the alternator. Mine put out 14.5 and 13.5 under full electrical load...until it didn't, quit on the way to The Vintage.

How accurate is the gauge?

 

[Stevehose]

Good point - I cleaned all contact points, grounds etc as well as put the relay on.

It's a false belief to throw a relay at it without solving the first issue. It will bite you sometime when you least expect it.( On the road to Vintage...)

 

[Arde]

It can be a weak battery, a weak alternator that does not charge it well, or corrosion at the battery connections proper. If the VDO takes the groung locally rather than through a direct wire to the battery then battery to chassis path could be it.

Corrosion at the bulb sockets is a long shot if you ask me. You can remove the bulbs to confirm that voltage does not drop and prove me right.

Increased electrical load does not cause a car to lurche on a six cylinder car . Only explanation is that voltage drop is affecting coil for example.

 

[rb1971]

Thanks for all the thoughts. I should have probably mentioned that I am running an Optima Gel battery - and although it's neat tech I've never loved it, and my mechanic has had a few problems with his gel batteries on motorcycles in the past year. So after a test today confirmed that the alternator is doing its job, we are just going to try switching to a conventional battery to see if that makes a difference.