Understanding Headlight Function

[sidevalvepete]

I am endeavoring to up skill on how the headlights function on my late 30s mopar. In particular the relationships between the bulb, bulb holders(cable and socket assembly in the parts book),reflectors and glass lenses. My vehicle is a right hand drive version and perhaps this  is a factor too. One of my original headlight lenses was cracked and I haven't been able to get a replacement yet, hence my quest to understand how they work.

 

I bought a matching pair of USA domestic lenses to see if they would work, to match my 1938 Dodge. They fit the bucket and are identical in shape to my single original lens but have a different pattern. My original is held on the left and as well as the different pattern it has "EXPORT" embossed on it under the Made in USA script. See picture....

My reflectors, like the single original lens, have "EXPORT" stamped on them. So the car was equipped with the complete EXPORT light assembly. The two versions are listed in the parts book. The parts book also has a different bulb for the EXPORT version. As are the cable and socket assemblies. See difference in picture. The reflectors, cable and socket assemblies and bulbs fit together one way only that I presume aligns to make the beam at its brightest, focused and with the low beam dipping and maybe to the side. I say to the side because this would explain the need to be different between left and right hand drive vehicles. Is this why the lens options differ too? I have put Mazda 2331 bulbs in which are correct for the USA domestic headlights but align at about 2.00 o'clock not 12.00 o'clock like they should. An unmarked bulb I removed from car at disassembly is on the left in picture...

 

Does anyone have knowledge or technical data about this subject? Nothing in my Shop Manual or 1936-42 Mopar Service Manual to help me. My next step if nothing comes from this enquiry is to set up the car with a light board in front and do the trial and error thing with a range of different bulbs.

Apologies for the long winded post but trying to make my conundrum clear.

[dpollo]

I have faced this problem with a right hand steering 38 Dodge  which the owner brought with him from NZ when he came here in 1980.

 

It also had one cracked Export Lens which we changed to a generic North American  one.  The bulbs are prefocussed either 2330s or 2331, I cannot recall which but the terminals are  90 degrees different from 2330 to 2331.   These lights dip to the left as one would expect.   How that is accomplished , I cannot say.   If it were up to me, I would set the lights up to LHD standard which leaves you back where you started for advice.

 

I just thought you should know, your car has a twin   .  originally sold by Amuri Motors.

Edited January 28, 2021 by dpollo
spelling

[Andydodge]

The RHD/LHD difference is usually in the actual glass lens and the way the flutes are cast , at least thats with the 7" sealed beams, also the RHD bracketry that the reflector sits against should have the adjustment screws etc on opposite sides to that on a LHD car........interesting about the differing bulb holders.....have learnt something today...............andyd    

[greg g]

It probably related to the design of the components as to where the light goes in the patterns of light output.  The US lens will shine most of the light to the right side shoulder and away from incoming drivers,where as UK type of lenses would favor the right sholder. Also US regs probably also favored a lower fit off line for high beams.

 

I have euro conversion lamps in my Studebaker truck Got the from a friend who had put themin an MGB. But when he had them in his car he was always getting flashed even on low beam.  He discovered the were right hand drive highways and directed the light right into oncoming drivers eyes.  Since I don't drive at night, they aren't an issue.  Several people have remarked on the foreign looking head lamps.

[sidevalvepete]

11 hours ago, dpollo said:

 The bulbs are prefocussed either 2330s or 2331, I cannot recall which but the terminals are  90 degrees different from 2330 to 2331.   These lights dip to the left as one would expect.   How that is accomplished , I cannot say.  

You have given me a start. I know the 2331 bulb matches the US setup so will source some 2330 bulbs to try. If I go completely US configuration I will need matching reflectors and bulb holders for this model. Thinking about the high beam/low beam, left and right hand drive differences in beam angle and design of lens pattern shows how advanced the thinking and what was supplied into the market for motor vehicles was in those pre war days.

Am still keen to see some literature around this. Thanks to all for replies so far.☺

[desoto1939]

The 2331 bulb US style has the following orientation for low and high beam.   When looking at the socket and the pigtail buttons the low beam button  is at the approx 9 o clcok position and the high bean is at the 3 o clock position. This is what is on my 39 desoto the same 2331 bulbs.  So you need to know the correct bulb for your headlight socket setup.

 

so when in the car  the operation is a left movement for high beam and at right movement back to low beam.  Also the prisims in the glass also help  with the lighting pattern of the beam.

 

But if you have an export the beam might have been different in that the 2330 socket is more of a standard of up and down lkight a more modern high low beam operation.

 

In the 2330 the pigtail button are at 12 and 6 so high beam is at 12 and the low beam is a 6 and also the prisims in the headlight glass also affect the beam spreading of the light.   Basically the two sockets are the same but th eonly difference is in the orintation of how the two buttons are setup in the socket.  You can chnage out the button kust by getting the proper pigtail inner parts for either up/down or left/right operation.

 

I have done this on several of the prefocus sockets. Have learn this trick several years ago. from Don Axlrod how specialised in 1939 and back headlight.

 

 

Rich HArtung

desoto1939@aol.com 

[sidevalvepete]

Many thanks Rich. Will use this info as I finalise this. Will get some 2331 bulbs and work out if I need to alter the orientation of the sockets. As you can see in my Parts Book, the Export version is different across lens, bulb, socket and reflector. To complicate it further,  the Part no.s for the bulbs have a Chrysler no. and not 2331, 2330 etc. Would be good to cross reference these numbers somewhere.

[sidevalvepete]

Also, do you have Don Axlrod's contact information. Would be interested in tapping into his knowledge...

[Dan Hiebert]

This is an interesting thread.  I am of the understanding that the light patterns would be dictated more by the prisms molded into the lenses than the bulbs or reflectors.  The bulbs just provide for the needed intensity.  Or else, why would one bulb fit so many applications, i.e., 2331 is also what our Terraplane uses.  I have a period original box for aftermarket lenses for Model As (it has the original Model A lenses in it, I'm assuming the aftermarket ones were put on the car) that touts an improved light pattern over the original.  It doesn't explain why, tho, and of course I don't have the originals to compare.  Maybe a difference between mass production considerations and the aftermarket's presumed ability to make a more refined product - because they don't necessarily have to mass produce it on the scale the car company did.  How the light hits the road would be subject to ever increasing Govt. (both domestic and foreign) safety regulations, how the bulb plugs in or how the circuit works would be differences (or advertised improvements) in engineering.  Just my thoughts.    

[Pete]

Both my 1939 and 1938 Mopars use the 2331 bulb. From my reading there is some indication that Harleys and some Fords use 2330.

 

[desoto1939]

The prisim or the cuts inthe factory glass are used to diffuse the light beam.  So try this to understand the importance of the correct lens.  Take a  flat lens in a flashlight the beam is straight out wards.  But if the lens had cuts or prisism it  spreads the light beam as needed also thus witht he correct bulbs either2330 or 2331 the movement of the filament inside the bulb directs the intensity of the beam to the correct cuts inthe glass..

 

Do not over think the issue.  The use of the correct bulb and the correct lens is so important that they work together to get the correct pattern on the road.  So if you used the 2330 in the car that was to use the 2331 then the high beam would not work correctly and the lights would not be aimed correctly and you would have lights blinding the oncoming car at night.

Her is a page fromthe MoPar standard parts lisiting catalog fromthe section on Lights  refer to the part number 128155  adn this will indicate the correct light bulb that was used a Mazda 2550  with candle power 50-21...

 

I have this catalog for all of the various small parts on a CD

 

 

 

Rich Hartung

Desoto1939@aol.com

 

[sidevalvepete]

1 hour ago, desoto1939 said:

The prisim or the cuts inthe factory glass are used to diffuse the light beam.  So try this to understand the importance of the correct lens.  Take a  flat lens in a flashlight the beam is straight out wards.  But if the lens had cuts or prisism it  spreads the light beam as needed also thus witht he correct bulbs either2330 or 2331 the movement of the filament inside the bulb directs the intensity of the beam to the correct cuts inthe glass..

 

Do not over think the issue.  The use of the correct bulb and the correct lens is so important that they work together to get the correct pattern on the road.  So if you used the 2330 in the car that was to use the 2331 then the high beam would not work correctly and the lights would not be aimed correctly and you would have lights blinding the oncoming car at night.

Her is a page fromthe MoPar standard parts lisiting catalog fromthe section on Lights  refer to the part number 128155  adn this will indicate the correct light bulb that was used a Mazda 2550  with candle power 50-21...

 

I have this catalog for all of the various small parts on a CD

 

 

 

Rich Hartung

Desoto1939@aol.com

 

Excellent! Thanks for your help Rich. And your library!