348 Strange headlight issue

Is this low (dipped) and high beam? Did you check for power going to both low and high beam fuses?

I don't have a complete wiring diagram for US cars, but there is a single relay supplying power to both Left and Right low beam headlight fuses. It sounds like you have a relay panel circuit board issue. How did you check the voltage? On probe on the fuse (either end) and one probe on ground. Do you have continuity between pin 30 of the low beam relay (socket) and the RH low beam fuse?

Note that sometimes the metal frame of the relay panel is not a good ground.

USA cars have additional low/high beam relays (not on the frunk relay panel) which can affect headlamp operation, but if you're not getting power to the fuse, the issue is further upstream in frunk relay panel itself.

 

I presume you are referring to the low beams when you say "headlights". Do both, LH and RH, high beams work?

The fuses, 11 & 12, for the RH and LH low beams are connected to each other at their incoming power ends and receive power from the relay "e" (see the diagram below, trunk fuse box). So, with ignition "on", if you have power on the incoming side of one fuse you should also have power on the incoming side of the other, unless there is a problem with their link inside the fuse box. So, you should first verify that these two fuses both have power (at ignition "on"). If only the incoming side of the LH fuse has power and the incoming side of the RH does not, you have a problem inside the box.

The next thing to check: I have read that on US models the power from the fuses 11 & 12 does not go directly to the bulbs but first goes to two change-over relays (one for the RH and one for the LH low beam) and from these relays the power goes to the RH and LH low beam bulbs. It is likely that the change-over relay for your RH low beam is faulty. These two relays, being additional for the US market, are probably not in the trunk fuse box but mounted somewhere between the fuse box and the headlamps.

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Which relay did you replace, relay "e" in the trunk fuse/relay box? You should look for the two additional relays I mentioned. They should be somewhere in the trunk, between the fuse box and the headlamp plugs for the high/low bulbs.

 

Relay "e" provides power to both sides so, if one side works, the relay is good. I do not know where exactly these change-over relays are, perhaps someone having a US version 348 will provide info. Otherwise, you need to remove the trunk lining and look around/under the fuse box. If not there, try to follow the harness from the fuse box going towards the headlights.

According to what I have read, on US models, these two relays are there to disconnect the power to the low beams when the high beams are switched "on". I guess this is the law requirement there, the EURO models do not have these. You can try listening for clicks, other than the clicks of the relays "e" and "f", in the trunk area as the lights are toggled between high and low (maybe you would need to cover the relays "e" and "f" with something to muffle their sounds).

 

Just found this picture, the change-over relays are maybe the two sitting at the side of the fuse box (one shown pulled out). You can try swapping these two relays, if they are same, and see if the problem moves to the other side. This type of relay is called "change-over relay" (5 pins, including pins 87 and 87a) and it is easily available. Use the relay diagram at its side and the pin markings to order a correct type replacement relay.

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The relay diagram:
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On second look at the picture I attached above, the two "external" relays may not be additional relays for the low beams. Perhaps you'll have to try to find other "hidden" relays.

 

Not sure what you mean by "one had continuity, the other (?) should have had 12v when on and it didn't". Did both headlights have continuity? If the bad headlight had continuity between the fuse and the plug, then the additional relay should be ok. The relay sits betweent the fuse and the headlight.

What made you suspect that these may not be the headlight relays, Miro?

 

Here is a "work in progress" diagram for USA headlights...

https://www.dropbox.com/t/dV6jHjxPAgNj3q6Y

No wire colours for the additional relays.

 

I think that it was probably seeing your diagram (which I didn't keep) a few years ago for the US headlights what I had in memory as "I have read".

The reason why I suspected that the two relays attached to the side of the fuse box may not be the relays that would switch the low beams off when the high beams are switched on is what I could see looking at the socket of the relay that is shown as pulled out. The socket does not have a female contact in the centre which is for the relay pin 87a (normally closed) which would normally be used to cut-off power to something when the relay is energised (by the signal from the high beams being switched "on" in the case of the US headlights wiring). I also thought that, if the low beams need to be switched "off" when the high beams are switched "on" it would not be necessary to have two relays for the "change-over" as one relay could do the function (unless there is a special reason to have two relays, one for RH and one for LH).

 

Weird. I rechecked the blurry photo of a USA paper wiring diagram someone sent me and it is the same as my diagram.

Although there is a left and right relay, as you say, 87a (NC) is not pinned.

 

I think the picture I posted is of a Canadian model, not US, which uses the two extra relays for other purposes.

 

Canada usually insists on daytime running lights. I guess that might keep the front fog/flashers on?