Low Beams Circuit Failure - Wiring Diagram?

[RABID_MP5]

I'm working on a 2000 Protege right now. I think it's headlights are wired the same as my 02 P5. Anyway, the low beams don't work. You do hear a relay click when you rotate the switch to the headlight on position. And 12 volts then appears at the headlight bulb socket. The thing here is, it seems to be that the 12V is being applied to the "ground" of the bulb. Then the "hot" bulb leads for low and high are alternately grounded by the high/low part of the light switch, thus completing the circuit and lighting the appropriate bulb filiment(s).

I figured this by extensive analysis. It took awhile since it defies what I assumed to be true. Anyway I'm dying for either an explanation or better yet a wiring diagram that INCLUDES the headlight circuit. I have a diagram for the 02 P5, but it is labelled as a Wiring Diagram SUPPLEMENT. It seems like several sections are missing. Maybe this only includes sections that were revised or something.

Specifically, I need E-1, E-2, E-3, E-4a and E-4b. I'm not sure which shows what I need to see. These sections are referenced in a box on page W, which is included in what I have.

I've got 3 hours in this already. Any help would be MUCH appreciated.

 

[flash75]

The 2002 Protege wiring diagram and shop manual has a link at the top of this forum.

Don't know if it's the same as your car, the 2002 sedan and 2002 P5 have different diagrams. Using ground for switching is normal for most cars. Your lights aren't competing for ground. Check that the low beam filaments have 12 volts at the bulb with lights switched on and in the low beam position.

When the lights are off there will be 12 volts on the wire between the bulb and the switch. That voltage will disappear when the lights are switched on, the filament is the load.

Clifton

 

[njaremka]

so, you are getting 12v at the socket, and the low beams dont work? are the bulbs good?

 

[RABID_MP5]

Yeah I got these to work last night. Apparently the ground for the low beams, which I believe is just a fixed ground to chassis, had been lost due to connector corrosion or harness failure. So I just grounded the low beam filiments off each bulb socket to the car. Easier than chasing it down. It's a fixed ground because the lights switch & relay only give the 12V to the headlamps when the main switch is rotated to the "lights on" position, plus the low filiments are supposed to stay lit when you switch on the high beams. (You also get 12V there when you use the brights flasher.) Luckily it wasn't the high beams, where the ground is switched by the control lever.

I'll recheck the link for the diagram. Again I got one off Ugly Protege a couple years ago, but it's a supplement that's incomplete.

 

[njaremka]

actually, the low beam on the protege's should turn off when you select the high beam. on the protege5 the lows stay on, but on the sedan the lows turn off.

 

[RABID_MP5]

hmm, thanks. Well if so, then I guess that implies my high/low switch may really be defective. (boom02)
Hmm, but I'm getting more light now - IF the 9003 can take having both filaments lit at once and IF the 12V wire, relay, and fuse can take the 60+65W load on high.
I'm real iffy on the second part - only lit them up several seconds testing. But I could rig a relay to get the 12V from basically the battery (like many HID refit guys do). This might even give a bit more light due to less resistance. I'm wondering if running both filaments is OK in itself? I could melt the lamp plastic?

 

[njaremka]

hmm, thanks. Well if so, then I guess that implies my high/low switch may really be defective. (boom02)
Hmm, but I'm getting more light now - IF the 9003 can take having both filaments lit at once and IF the 12V wire, relay, and fuse can take the 60+65W load on high.
I'm real iffy on the second part - only lit them up several seconds testing. But I could rig a relay to get the 12V from basically the battery (like many HID refit guys do). This might even give a bit more light due to less resistance. I'm wondering if running both filaments is OK in itself? I could melt the lamp plastic?

you would be making a LOT of heat in the bulb. i'd be worried about the bulb bursting from the heat, not to mention the housing.

the protege sedan uses a ground-switching circuit, as was already mentioned. it sends constant 12v tot he bulb, then switches the ground wires on and off - for both the low and high. if you have the ability, i would check to make sure you are getting 12v at the bulb connector, then check the wiring from the bulb to the switch, then pull the switch and check the contacts for resistance while switching it on and off.