Low beam/High beam issues. Possibly PO related.

[mmmb00st]

Quick question that perhaps some of you have run into. My low beams do not function if I pull the headlight switch out to the on position. If I push forward on the stalk and turn on my high beams, all 4 lights come on. At first I thought I had an underlying wiring issue, but the more I discover about this car, the more I wouldn't put it past the PO to have changed the wiring to this configuration on purpose.

Car is an 86' 325e, "I" swapped with all associated swap parts. When all lights are on, I have zero issues with light output. No slightly dimmer lights than others. Could it be my headlight switch? The reason I am questioning myself on that theory is because to the best of my understanding, when you flip your highs on, the lows are supposed to go off until the highs are turned back off. Correct? Which would mean that low and high are on the same circuit currently. The more I try to wrap my brain around why the lights work in this fashion, the more I feel like I'm drifting off into the twilight zone or some shit. Am I overthinking it and just need to replace my headlight switch? Or did the PO wire the low beams into the high beam wiring? Any other alternate realities that could be possible? Some sort of relay jumper?

Thanks in advance for whatever help comes,
-Brandon

[ELVA164]

Quick question that perhaps some of you have run into. My low beams do not function if I pull the headlight switch out to the on position. If I push forward on the stalk and turn on my high beams, all 4 lights come on. At first I thought I had an underlying wiring issue, but the more I discover about this car, the more I wouldn't put it past the PO to have changed the wiring to this configuration on purpose.

Car is an 86' 325e, "I" swapped with all associated swap parts. When all lights are on, I have zero issues with light output. No slightly dimmer lights than others. Could it be my headlight switch? The reason I am questioning myself on that theory is because to the best of my understanding, when you flip your highs on, the lows are supposed to go off until the highs are turned back off. Correct? Which would mean that low and high are on the same circuit currently. The more I try to wrap my brain around why the lights work in this fashion, the more I feel like I'm drifting off into the twilight zone or some shit. Am I overthinking it and just need to replace my headlight switch? Or did the PO wire the low beams into the high beam wiring? Any other alternate realities that could be possible? Some sort of relay jumper?

Thanks in advance for whatever help comes,
-Brandon

First things first: Which headlights do you have? If you have sealed beams or H4 low beams, it sounds like normal operation except the low brands aren't getting power. If you have any type of single filament low beams,
some type of jumper has been used. Either way, the first step is to pull the power wire for each low beam separately, turn the headlight switch on, and see if it's getting power.

[mmmb00st]

First things first: Which headlights do you have? If you have sealed beams or H4 low beams, it sounds like normal operation except the low brands aren't getting power. If you have any type of single filament low beams,
some type of jumper has been used. Either way, the first step is to pull the power wire for each low beam separately, turn the headlight switch on, and see if it's getting power.

Sorry. They are sealed beams. Normally I would test for power at the connector, but I know I'm not getting power when the headlight switch is pulled. I also already know that the low beams DO in fact receive power when the high beam power is applied. So, if you are correct in the understanding that sealed beam lows function while highs are on, then I am absolutely leaning towards my switch and or relay. Based on your extensive knowledge, does this appear to be more of a relay issue, or just a switch issue? I have noticed that when I pull my headlight switch, sometimes some of my interior light will not illuminate properly until I push/pull the switch a time or two. But that's quite rare.

Thanks again, Elva (Michael? Mike? lol)
-Brandon

[ELVA164]

Sorry. They are sealed beams. Normally I would test for power at the connector, but I know I'm not getting power when the headlight switch is pulled. I also already know that the low beams DO in fact receive power when the high beam power is applied. So, if you are correct in the understanding that sealed beam lows function while highs are on, then I am absolutely leaning towards my switch and or relay. Based on your extensive knowledge, does this appear to be more of a relay issue, or just a switch issue? I have noticed that when I pull my headlight switch, sometimes some of my interior light will not illuminate properly until I push/pull the switch a time or two. But that's quite rare.

Thanks again, Elva (Michael? Mike? lol)
-Brandon

Haha, Mike is fine. Sealed low beams have three wires: low beam power, high beam power, and ground. There are two filaments in the bulb. If you know you have power to each low beam wire at the light, then you just need to replace the two low beams. They're cheap and readily available (although I'd suggest an upgrade to an H4 light). If you mean the high beam wire gets power, then that suggests the switch is at least partially working. Otherwise the high beams would only work in the "flash" position on the stalk. It does sound like the rheostat is worn, so the switch may be as well. There are two low beam relays; if you could find or buy a new or known good one, I'd try it in both positions. Hope that helps, at least to start.

[Das Delfin]

With sealed beams there are two filaments in the low beam lights. When you switch on your high beams, one filament turns off and another turns on. So all four of your lights come on with high beams, but it is a different filament and a different circuit than what comes on in the low beams.

Your L/R low beams are also on two different fuses

Try a new low beam relay first. Check to see if your horn relay is the same type and plug that in instead to check

If that doesn't work try replacing the headlight switch

[mmmb00st]

Very good info, fellas. I greatly appreciate it. Knowing that they are dual-filament is important. As the lows only function when the highs are either pulled(flicked) or pushed(on), I wonder if I do actually have a dead fuse or relay for the low beam, single filament side of the bulb. I'll get on to diagnosing.

Thanks for the head start fellas,
-Brandon

[navid41691]

Any update on this? Did you fix the issue? What was it?