Low/High Beam Both on -

[JK McDonald]

This weekend I was helping a friend troubleshoot a headlight problem on his 1980 911. As expected, after pulling the steering wheel I found that the Headlight Low-High beam switch contacts needed to be cleaned. But.... once I had everything working again I noticed something very different in the way the headlights were wired.

A previous owner had completely bypassed the steering wheel low beam switch contact. He'd run power to the left/right Low Beam Fuses directly from the instrument panel headlight switch when pulled completely out. The steering wheel control switch still provides power to the High Beam Fuses when it is levered/pushed in. The headlight low beam appears to turn on normally as expected - but when the high beam is selected "ALL Four (Low/High) Filaments are on......

Over the last couple of years of ownership, my buddy evidently passed the Texas Safety inspection with flying colors and hadn't even realized his headlights were not working normally.

I know some of the early U.S. 4 headlight cars would have both sets of their sealed beams come on when the high beams were selected. Other than putting out a Lot of Light - it doesn't seem to have over loaded the electrics ? I did recommended that he at least install a "Headlight Relay Kit"....

Michael

[JSV798]

On my '78SC when high beam is selected low beam remains on. I think this is normal. So, yes I have fitted relays

[proporsche]

if you have the high beam on, the low beam should be off..do some search here how to adjust your turn signal switch...

Ivan

[famoroso]

What type of headlights? H1s, or...?

[JK McDonald]

My friend's 1980 911 has the old standard dual filament sealed beam headlights. I'd assumed that his "Low and High" Beams should normally run off separate circuits (like all my cars) with each filament turning on one at a time.

With both "Low and High" beams burning when the High Beams are selected for several years of ownership - he has never blown any fuses or smoked his alternator... I looked over the wiring harness under the dash and along the fuse panel and didn't find any electrical overload or damage.

To restore his headlights to the original factory operation he does need a new "Turn Signal-Headlight Low/High Beam Switch Assembly", but I don't think it's planned. I have convinced him to order one of the "Headlight Relay Kits" for our next project....

I was just wondering if any one else has seen this issue ?

Michael

[Targalid]

Have I seen this issue? Yes. My old switch needs a yearly adjustment with small cardboard strips to correctly space the contacts or my low and high beams will both light at the same time. I am working on replacing the guts of this swtich with cheap microswitches from Ebay. The switch was the pinnacle of technology in 1970 but not so much these days, 50 years later. I have the relay kit but once the switch has been cooked I think it will never quite be the same.

[dap930]

There is a provision in the wiring harness that allows direct power from the headlight switch to the low beams bypassing the low beam contacts in the high/low beam stalk switch. This allows the low beams to stay on when the high beams are on. This setup is shown connected in the wiring diagram. For USA cars, the wire (yel) from the headlight switch is disconnected and the (yel) wire from the stalk switch is connected to the low beams. So, check that someone has not connected the headlights in the European configuration.

[JSV798]

The headlights wiring diagram on page 970-19 in Bentley shows low beam going off when high beam selected but in Haynes on page 298, fuse 6 (yellow wire - low beam) is connected directly to light switch terminal 56 so low beams will stay on. Yellow wire emerging from dimmer switch terminates on diagram at T1f whatever that means - perhaps someone can explain?

[dap930]

T1f refers to the bayonet connector at the end of the yel wire coming from the dimmer switch. For USA cars, T1f should be connected to T6d in the Haynes schematic. I used to switch my car back and forth to pass state inspection.

[JSV798]

Originally Posted by JSV798

The headlights wiring diagram on page 970-19 in Bentley shows low beam going off when high beam selected but in Haynes on page 298, fuse 6 (yellow wire - low beam) is connected directly to light switch terminal 56 so low beams will stay on. Yellow wire emerging from dimmer switch terminates on diagram at T1f whatever that means - perhaps someone can explain?

Think I can now answer my own question. Recently, the steering column bush failed on my car so had to remove the steering wheel and fit a new bush. There is a fix that involves using a 928 numbered part ( 92834773902 ). While I had the steering wheel off I checked out the dip switch as I have seen threads on how these contacts can get out of line but all was well. Five years ago I installed relays and am relieved that that both the light switch and dip switch have survived. But I was still concerned that when high beam was selected, low beam stayed on. Careful study of the wiring diagrams in the Haynes manual revealed that the 1982 wiring diagram ( page 311 ) showed that the yellow wire exiting the dip switch was connected to fuse 6 and the yellow wire from light switch terminal 56 was absent.
Searching under the dash near the light switch I found a (loose) yellow wire and confirmed with my test lamp that the dip switch did indeed control it. This is terminal T1f. I disconnected the yellow wire on terminal 56 at the light switch and connected it to this spare yellow wire; it so happened that one had a male connector and the other a female connector. I now have a low beam that goes out when high beam is selected as on later cars. You may want to carry out the easy modification yourself.

[911obgyn]

Another project to put on the list for that car is replacing old sealed beam headlights with H4 while you are there. You can pick up a pair for less than 100 makes driving at night so much better.

[HarryD]

Originally Posted by 911obgyn

Another project to put on the list for that car is replacing old sealed beam headlights with H4 while you are there. You can pick up a pair for less than 100 makes driving at night so much better.

Definite improvement.

I originally replaced my sealed beams with the Hella H-4 7" "off road/E code" units.

A few months back, one of the glass lenses got cracked. I was going to replace that unit at a cost of $70+. On Amazon, I found a set of 7" LED replacement units for $50+. They dropped right in and the improvement over the H-4's was noticeable. If you do not object to a more modern headlight in your car, go with the LED units.

Some interesting discussion: https://forums.pelicanparts.com/porsche-911-technical-forum/1159678-diy-led-headlight-conversion.html