headlight wiring weird voltage?

[Phizinza]

Ok first up, only those who have played with or understand Subaru (and most other jap car makers) headlight wiring will know what I'm talking about...

 

When the steering column dip switch is on low beam the Red/White wire from that to the headlights (highbeam) should be disconnected and no current or voltage as it is then an open circuit. But no, theres about 6V with a 60mA current draw still. Its the same when on High beam the low beam Red/Black wire has 6V's on it.

I've noticed this a while ago in my old Brumby but its been annoying me while doing a relay mod to the headlights in my 83 sedan. What happened was that 6V was enough to hold the relays on. I've found the solution with these resistor relays (they have a resistor in between both pins of the coil which draws that current away so the relay can turn "off").

But it still bugs me I can't find where this power is coming form. On the high beam it makes a little sense because the high beam light is earthed on one end, and because the headlights are common positive this could let power be drawn through the headlight and the dash light to feed that relay. But on the low beam it should be a straight wire from the dip switch to the headlights. My manual says it doesn't go anywhere else. But I'm not willing to open up the entire loom to find where this wire goes and where this power could be coming from.

 

Anyone else noticed this? Anyone know what causes it?

[TomRhere]

The voltage you're seeing is coming thru the filaments of the headlights. Yes, they are being fed with 12VDC, but the resistance of the filament wire(s) is dropping that down to 6VDC.

 

You will have that voltage on the wires from headlight to switch, as the switch makes the connection to battery - for the circuit.

 

Now, that will only stand true if the bulbs are plugged in. If you're seeing voltage on those wires with the bulbs un-plugged, seems there would be a wiring issue. But I'm thinking you don't have voltage when they're un-plugged.

 

edit:

 

FYI. There are alot of DC electrical devices that will operate at a lower voltage than what they are rated for. We use 24VDC control devices on our machines at work. Most of them will operate on 3 to 28 VDC. We use resistors and or diodes to keep things properly switched and controlled.

Edited April 1, 2009 by TomRhere
added info

[Phizinza]

... Here's a circuit diagram of my headlight wiring, now modified with relays.

 

I've drawn a red line on the Low beam's negative. Now if that switch that turns to high beam and low beam wire is no longer connected (I've confirmed the dip switch does break the circuit 100%). Surely there is no way the coil on the relay can have power if that negative through the dip switch is broken (keep in mind the original wiring no longer goes to the headlights)?

[naru]

If your diagram is correct,the high beam relay coil is grounding through the indicator bulb w/the dip switch in the low beam position.

 

Also,the indicator won`t light in the high beam position as there is a direct path to ground through the dip switch.

 

Did you really rewire everything?Looks much different than stock.

[subiemech85]

would it work better if the relay was used to send power to the bulb, and the old wiring to trip the relay?

 

battery 30

sealed beam 87

old wire for sealed beam 86

ground 85

 

IIRC 87B is a second 87 that will have power from 30 when 87 does

87A will have power from 30 when 87 does NOT

[Phizinza]

The headlights are common positive. So keeping that in mind, you cannot run the low beam and high beam light through a relay to ground. I've just run them to the original headlights positive.

My headlights are now common negative, and the relays "30" is connected to positive. Just like the diagram shows.

 

Basically, right next to the battery I cut into the loom. I cut the four headlight wires, R RL RW RB. I then connected R and RB through 85 and 86 one and RL, RW on the other. Then the headlight side of RB went on the first relays 87 and the RW went on the second relays 87. The headlight side of R and RL (originally the common positive for the headlights) then went to ground on the battery. I added some wires from battery to a fuse box then onto the relays 30's. So only added wires were the fused 30's and extension for the R RL off the headlight to the battery negative.

Of cause I also added the spot lights in which have a switch in the cabin that lights up when the spotties are on, so this needed to be wired like it is in the diagram for the light to work in that switch. The require two wires going from the spotties relay to that switch and some grounding wires.

 

Heres a stock diagram I setup

[Cougar]

Naru is correct. You need to move the indicator lamp lead to the other side of the relay coil and the ground side of the lamp will run through the swtich.

[Phizinza]

Yes, I understand that and I realise it could (probably is) cause the problem on the high beam side of things... But there is the same voltage on the low beam. Now I'm only going on what my Gregory's manual tells me and that is the wire from the dip switch to the head lights has no more things connected to it. So from the dip switch to my new low beam relay there should be a straight wire with no connections.

[Cougar]

I see you changed the drawing. The way you now show it the low beams should work ok when the dip switch makes the ground connection for the low beams. As a note, I assume you have checked the current rating for the dip switch and it can handle the current load for both of the lights.

 

The indicator light for the high beams is still not connected correctly. You have a common power lead to the lights and though you may have the low beams selected there is still going to be current flow through the high beams because the indicator light makes a path to ground for them. You need to connect that light in parallel with the high beams so no ground is made until the dip switch is turned on.

[Phizinza]

I didn't change the drawing.....

 

Just ignore the spot light wiring because I have the same problem without all that wiring.

 

I posted a standard wiring diagram, and also my modified one which is above (the first one I posted).

 

Oh, and BTW the "dip switch" is what I call the original high low beam selecting switch the all cars come with that is on the steering column. It is rated for BLOODY high amperage. And all it is doing now is switching a relay that needs little more then 50mA.

 

 

So heres a diagram without the spot lights...

[Cougar]

You still have the high beam indicator light connected wrong. Current will run through the high beam relay coil and the light when the dip switch is on the low beam selection and when on the high beam the dip switch will bypass the light to ground. Just tie that light to one of the leads of one of the high beam lights and it will work ok.

[Phizinza]

....... That is how the high beam is wired standard, I did not wire it like that. I know that is where some leaking current can come from but I do not understand how the low beam wire has the same voltage and current as it has no light, nothing, attached to it in the diagram.

 

Please read

But it still bugs me I can't find where this power is coming form. On the high beam it makes a little sense because the high beam light is earthed on one end, and because the headlights are common positive this could let power be drawn through the headlight and the dash light to feed that relay. But on the low beam it should be a straight wire from the dip switch to the headlights. My manual says it doesn't go anywhere else. But I'm not willing to open up the entire loom to find where this wire goes and where this power could be coming from.

I want to ignore the highbeam for now (like I tried to make clear in all my other posts) because it is not related to the low beam wire having 6v when it shouldn't

[Cougar]

I'm not sure where you are testing the voltage at and what you are using to test with. I assume you are looking at the ground side of the light with the circuit open. You may not have a high impedance voltmeter and your test equipment is loading the circuit and causes an error in the reading. A digital meter should not have this problem.

Edited April 4, 2009 by Cougar

[Phizinza]

Ok, found the it. Sorry for discrediting your high beam light theory. My manual doesn't show this, but the high beam light is actually connected between the high and low beam wires from the switch to the headlights. So when your on high beam the indicator light is connected to ground through the high beam wire and to positive through the low beam wire through the low bead filament through the original headlight relays.

 

Man do they want it to be confusing when making these cars. Would of made sense if my manual didn't show the low beam wire going from the switch to the low beam filaments without any interruption.

[Cougar]

Glad you got it connected right. As a note, in the later factory maunal like for my '88 model, the power wiring to the headlights is drawn incorrectly on one of the main wiring pages. It shows the power wire going to one side of the two headlights instead of in between the two lights that really have a switched ground on the other side of the filaments to turn on the lights.