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Headlight puzzle

Posted: Sat Sep 07, 2019 1:15 pm
by Steven Unterman
Hi folks,

I have a 1965 356C. Years ago I installed one of Joe Leoni's headlight relays and a couple of years ago I installed a pair of Jeff Fellman's SMD headlights. For what it's worth the car is the original 6 volts A few months ago I noticed that one of the headlights seemed to flicker a bit. Figured it might just be a poor connection but then a month or so later both headlights just quit working and wouldn't come on when I was driving the car. What seems odd to me is that a couple of weeks ago I noticed that with the car off and no key in the ignition I can pull the light switch on and both headlights turn on just fine.

Any thoughts among those of you who know these cars better than I do? Any help would really be appreciated.

Thanks,
Steve

Re: Headlight puzzle

Posted: Sat Sep 07, 2019 2:44 pm
by David Jones
Rather a strange problem and I would think that checking the voltage of the generator is where I would start. If you had an AC component on the generator output I guess in theory that would cause a flickering LED. Reverse polarity would put them out but if that occurred then the battery would not charge. Set your voltmeter on AC and see if there is an AC component on the DC value. Not enough voltage to trigger the SMD while running will also do it.

Re: Headlight puzzle

Posted: Sat Sep 07, 2019 9:16 pm
by Martin Benade
Is your running voltage too low (below 6 v) for them to light but the car still manages to start?

Re: Headlight puzzle

Posted: Sun Sep 08, 2019 2:46 am
by Harlan Halsey
I would check your grounds.

Re: Headlight puzzle

Posted: Sun Sep 08, 2019 12:29 pm
by Steven Unterman
Really appreciate the feedback. Sounds like this might be a low voltage problem. Unfortunately I'm electrically challenged. It's my understanding that to check this I need to have the car running. Do I touch one lead of the voltmeter to the D+ terminal of the generator and the other lead to any random ground on the chassis? Do I use the ground on the regulator or do I use the D+ terminal on the regulator and any random ground?

Thanks in advance for any help.

Steve

Re: Headlight puzzle

Posted: Sun Sep 08, 2019 12:38 pm
by David Jones
Check at the battery across + and - terminals with and without engine running then with engine running at at least 2K rpm check at the regulator across Bat+ to gen ground then with engine at idle check same. With engine running at revs you should see the voltage rise to a max of 7.3 volts. That may not occur until you reach 3K rpm but you are looking for at least the voltage to rise by at least 0.5 volts above battery voltage with engine off. If all looks well the proceed to check voltage at the headlight fuses with engine running at 2K or above rpm. With a digital voltmeter it does not matter which way round the terminals are as long as they are across battery positive and a good ground.

Re: Headlight puzzle

Posted: Sun Sep 08, 2019 1:08 pm
by Steven Unterman
Thanks, David. If I recall you helped me trouble shoot some problems I was having when I got my 356 years ago. When you talk about checking at the regulator "across Bat+ to gen ground" I'm assuming that's the terminal on the upper right of the regulator to the ground terminal on the top of the generator. Is that correct?

For what it's worth I also have a lead from the B+ regulator terminal that goes to a relay for a third brake light, but I'm thinking this shouldn't make any difference.

Appreciate your time with this. Will let the group know how things turn out.

Steve

Re: Headlight puzzle

Posted: Sun Sep 08, 2019 2:23 pm
by David Jones
Steve, I usually put my ground lead on the gen case as that should be as good a ground as you get anywhere. The Bat+ on the reg is better than going to the Gen + as that will show the battery voltage until the regulator relay closes then you will see it rise higher than battery voltage though either will work in reality.

Re: Headlight puzzle

Posted: Tue Sep 10, 2019 8:50 pm
by Steven Unterman
OK - the plot thickens. Although the headlights haven't come on the last few times I tried, when I drove the car yesterday they came on. At idle the passenger side seems dimmer than the driver's side and sporadically flickers. When I rev the car both lights appear equally brighter and there is no flickering. There are 6.19 volts across the battery terminals when the car is off. This goes up to 6.76 volts at 2000 rpm. At idle (around 700 rpm) regulator Bat+ terminal to generator ground is 6.04 volts. At 2000 rpm this increases to 7.1 volts. Any thoughts? Help is certainly appreciated.

Thanks,
Steve

Re: Headlight puzzle

Posted: Tue Sep 10, 2019 10:03 pm
by David Jones
Check the headlight ground connections Steve. They are in the front trunk on either side. They come through the tube for the horn mount/fender brace at the inner fender wall and must be clean and make a good ground.

Re: Headlight puzzle

Posted: Wed Sep 11, 2019 12:30 pm
by Greg Bryan
Steve - you might try substituting the conventional headlight lamps for the SMD headlights to see if the problem goes away or persists. It sounds like the SMD headlights are just on the threshold of their operating voltage, and sometimes they light and sometimes they don't. I seem to remember other threads from the past with similar issues.
Of course, you have received lots of good advice above regarding checking connections and grounds. You may be fighting a number of voltage drops across various components although the Leoni kit should eliminate most of the common ones.

Re: Headlight puzzle

Posted: Fri Sep 27, 2019 12:30 am
by Steven Unterman
Hi Folks,
I spent a little bit of time cleaning up the ground connections in the right front truck. Also removed the right headlight and tightened up the receptacles for the 3 pronged connector and viola! the lights are bright and don't flicker any more.

Appreciate everyone's in put with this. Haven't used 356 talk in many years - great resource.

Thanks,
Steve

Re: Headlight puzzle

Posted: Fri Sep 27, 2019 11:13 am
by Wes Bender
I knew a gal who used to play one of them there violas...

Re: Headlight puzzle

Posted: Fri Sep 27, 2019 11:54 am
by Steven Unterman
I guess I should have included the little accent mark over the "a" but then again I grew up in Oklahoma - not that there's anything wrong with that.

Re: Headlight puzzle

Posted: Fri Sep 27, 2019 12:01 pm
by Steven Unterman
Plus that would be VOILA. Okies rule