Headlights won’t go off

[Buische]

Hoping for some good advice. 1975 914 headlights won’t go off. Used continuity tester on switch posts 15 and 56, and only got beep when switch out fully, so seems fine.

Using Haynes manual wiring diagram. Shows 5 post relay for headlights, but only finding a 4 post relay with wires big enough for headlights on the fuse panel. Also, the wiring diagram on the relay itself (SWF R 200.925) shows 56a closed and F open, suggesting 56a is low beam. This is backward from the manual. Verified continuity between S, 56, and 56 a with relay in my hand and disconnected. F has no continuity with the others. Is as expected from the relay schematic.

I’m lost, don’t know what to think now. Any advice?

[Dave at Pelican Parts]

Are they actually lit at all times? Do the lights retract when you push the headlight switch in?

There is a five-pole relay at each headlight motor which controls it going up and down.

There is a four-pole high/low relay on top of the fuse board. That is likely the one you found. It only directs the power from the headlight switch to the high-beam circuits or to the low-beam circuits.

If the lights stay on all the time, the problem is most likely in the headlight switch or the wiring to the switch. If the behavior is not that, then there could be other problems.

--DD

[Buische]

Thanks. Yes and yes. Headlights stay on even when the light doors close.

The Haynes manual diagrams for all years show a 5 pole relay for the combination relay or headlight relay, same thing, different names early and late. I can see separate relays for the doors in an different part of the diagrams. I’ll post an image later when I get home.

Is it possible Haynes used 911 diagrams?.

I tested continuity between all switch terminals and 56, and found what I expected based on the switch schematic. I don’t know a better way to test the headlight switch without power to the car. I’m in the middle of a significant rewire and radiator relocation effort, so don’t want to connect power until it’s all buttoned up and I’m sure there are no loose hot wires and all is put back the best that I know how.

Any suggestions for bench testing the switch more thoroughly than I described?

Thanks,
Chuck

[Buische]

Another point that may support the theory that the diagrams are 911... wire colors and groups don’t always match, and I can tell they are factory, not some of the “hacktory” wiring I’m trying to clean up.

[Buische]

Ok, got home and looked again at the manual. Up through 74 it shows US with 4 pin relay and non-us with 5 pin. But the single 75 schematic does not specify, and shows 5 pin, so clearly non us. That may also explain a few wire colors and groupings not matching.

Still looking for experienced guidance on how to bench test the headlight switch beyond what I’ve already done.

Thanks.

[Dave at Pelican Parts]

The Haynes manual's diagrams are taken directly from the factory manual. They aren't 911 diagrams.

I'll dig into the diagrams I have and see if I can make sense of them... It's been a while since I've looked at that part of the circuits, though.

In the meantime, here's a look inside the switch with descriptions of its functionality:

https://members.rennlist.com/pbanders/headlight_switch_internals.htm

Courtesy of the amazing Brad Anders, who also has tons of D-Jetronic FI information elsewhere on that website.

--DD

[Dave at Pelican Parts]

OK, so the relevant part of the wiring diagram is pretty straight-forward.

Power comes into the switch through terminal #15. That power comes from terminal X on the ignition switch. When the switch is on (out 2 stops), it sends power to terminal 56, where it goes to the high/low relay which sends it to the fuses for the high-beam or low-beam lights.

If there is no continuity between terminal 15 and terminal 56, then power should not be getting to the lights. At least, not through the normal path. So it must be getting there some other way.

First, have you verified that the correct wires are connected to 15 and 56? 15 should have a solid red wire, and 56 should have a connector that has a red/white (that's red with white stripe) and a black/blue wire crimped into it. The black/blue goes to the fog light switch if one is present. If not, then it should be taped out of the way so it cannot short to anything. The red/white wire goes to the high/low beam relay, terminal 56.

With the fog light switch off, and the headlight switch off, the only way I see for power to get into this part of the circuit is through the red/white wire from the high/low relay. Two of the connections there go to the headlights, with one also going to the high beam indicator light and also to the fog light switch. But if the latter is off (or not present and the wire is disconnected and taped up) then power can't get in that way.

That leaves us with the S terminal of the high/low relay, which should have a yellow/red wire connected to it. That comes from terminal S on the turn signal switch, which is the high/low beam selector part. But the selector part connects that to a ground or disconnects it, and never connects power to it, so power should not be able to get in through there either.

It appears that you have wires that are misconnected somewhere. I think you'll have to examine the wire colors against the wiring diagram, and if nothing shows up there then you will have to hook the battery up (remove fuses 1-4 so the lights don't drain your battery) and start checking for 12V at various points along the way. Unplug stuff to separate the circuit into pieces so you can test those as you go along.

I hope this helps!

--DD

[Buische]

Thanks Dave. I’ll take another run at it tonight, my main fear being I didn’t detect a bad switch when it is bad but testing method didn’t uncover it. But there is every chance there is a short with a hot wire that I just haven’t noticed yet.

Thanks,
Chuck

[Dave at Pelican Parts]

Don't forget the fog light switch and wiring. It may be possible for power to back-feed into the headlight circuit through that.

--DD

[dr914]

pull the hi low beam and see if they stay on, if so there is a melted wire somewhere, if not then replace the hi low beam and wire correctly as the new relay has an extra terminal

Originally Posted by Buische

Hoping for some good advice. 1975 914 headlights won’t go off. Used continuity tester on switch posts 15 and 56, and only got beep when switch out fully, so seems fine.

Using Haynes manual wiring diagram. Shows 5 post relay for headlights, but only finding a 4 post relay with wires big enough for headlights on the fuse panel. Also, the wiring diagram on the relay itself (SWF R 200.925) shows 56a closed and F open, suggesting 56a is low beam. This is backward from the manual. Verified continuity between S, 56, and 56 a with relay in my hand and disconnected. F has no continuity with the others. Is as expected from the relay schematic.

I’m lost, don’t know what to think now. Any advice?

[Buische]

Originally Posted by Dave at Pelican Parts

Don't forget the fog light switch and wiring. It may be possible for power to back-feed into the headlight circuit through that.

--DD

Dave,

That is interesting. One of the areas with confusing and dubious wiring that I cleaned up. Maybe I need to do basic checks and just wait until I put it all back together in a couple of weeks, and see if there is still a problem.

Thanks,
Chuck

[Buische]

Originally Posted by dr914

pull the hi low beam and see if they stay on, if so there is a melted wire somewhere, if not then replace the hi low beam and wire correctly as the new relay has an extra terminal

That is a really easy check if still a problem when I put it back together.

Thanks,
Chuck

[Buische]

I am now starting to use the 1974 US schematic, crossed out the 1975 schematics that turn out to be nonUS, but don’t say anything. I now see a totally different picture and understand how power could cross over. Glad I know this now because I need to disable the factory fog light wiring. I replaced it with a separate system because what was in there was a mess and I didn’t trust anything. I suspect that I will have no problems now, but will perform the unpowered checks recommended by you guys for insurance.

Thanks,
Chuck

[Buische]

I removed the fog light relay from the circuit, isolated high and low beam wires at both ends, and checked continuity between power wires to cabin and headlight wires. No continuity with ign switch on or off, so not a short in the harness. Looking at notes from disassembly of dash wiring mess, it’s possible the PO added a power wire from an auxiliary fuse block to the wrong place, not having a clue about the system. Notes aren’t good enough to be sure. I expect things to work fine when I put it back together.

Thanks for the help.

[Buische]

In case anyone cares, I wired headlights per the manual and removed all the crap under the dash. Hooked up power finally, and after working through a bunch of corroded connections, found the headlights work fine. So it was definitely related to the "special" wiring added by the PO. I do have to jiggle the headlight switch pull sometimes when I turn on the lights, but I can live with that for now. Appreciate advice offered here.