Headlight Problem-No low beams-possible bad combination (dimmer) switch

[keith.abergel]

Hello all, I have dug through the old threads but cant seem to find anything that addresses testing the combination (dimmer) switch for the headlights on my '78 280z.

I have narrowed down the problem to the switch, I think. Bulbs are good, fuses are good, continuity of circuit from the switch to the bulbs is good, even the ground return path (red with black stripe for low beam return path, red with white stripe for high beam return path).

The headlight switch shown in in the picture has a white wire with red stripe that feeds constant power from the positive terminal of the battery (through fusible links first). When the dimmer switch for the headlights is in the high beam position, the switch completes the circuit when allowing the white with red stripe wire to feed power to the solid red wire which then goes on to the fuse box, and then splits into solid red (right headlight) and red with yellow stripe (left headlight). However, when the dimmer switch is in the low beam position, the solid red wire does not receive power since the rocker arm does not connect the white with red stripe wire (hot from battery) to the red wire as it does when in the high beam position. Is this how the switch is supposed to function? I already cleaned it thoroughly, contacts between rocker arm and pins are good.

Any help would be greatly appreciated.

[ATTACH=CONFIG]72653[/ATTACH]

Edited July 9, 2014 by keith.abergel

[SteveJ]

If your wiring is stock, here is how the circuit goes:

1. From the positive terminal, the circuit goes through the fusible link and up to the white/red wire and on to the combo switch.

2. When the switch is on the headlight position, the circuit is closed to the red wire that goes down to the fuse box.

3. At the fuse box, the red wire splits to the left and right fuses where it comes out as red/yellow (left) and red (right) and goes out to the headlights.

4. The circuits go through the headlights and come out as red/white (high) and red/black (low). The wires from the headlights merge and go back to the turn signal side of the switch.

5. The high/low beam switch will change which wire (r/b or r/w) is in contact with ground.

The FSM has a clear diagram on page BE-9

So if your low beams are not working, it is likely that there is a problem on the turn signal side of the switch. Moving the high/low beam switch will not affect the connection between the white/red and red wires. You may be using poor technique to measure voltage.

[keith.abergel]

Hi Steve, thanks for the reply. The wiring is indeed stock. The circuits for the high and low beams are exactly as you described. I was working off of that same wiring diagram from my FSM.

I understand that the dimmer switch changes the ground/return path for the circuit; between the red with white stripe for high, and red with black stripe for low beam. What I cant quite understand is how this is accomplished since the dimmer switch seems to be on the feeder (poor terminology sorry) side of the circuit and only opens and closes the power to the circuit (by connecting the white with red stripe to the solid red)? What am I missing here?

Thanks again.

[Captain Obvious]

Not really sure what you're asking, but here's another description of how the headlight system works...

When you turn on the switch on the multi-function stalk on the right hand side of the steering wheel it allows current flow from the battery, through the headlight switch, and to the headlights.

Out at the headlights, at any given time, only one of the two beam filaments is connected to anything. One of the filaments is hanging open (no-connect) and the other filament is connected to ground through the beam selector switch built into the turn signal switch on the left hand side of the steering wheel.

The filament that will light is the one that is grounded. The one that is no-connect will not light.

What your doing when you toggle HI/LO beams, is you toggle which of those two filaments is connected to ground and which one is hanging open.

[SteveJ]

Here's a crude drawing I made many years ago...

[Zed Head]

What I cant quite understand is how this is accomplished since the dimmer switch seems to be on the feeder (poor terminology sorry) side of the circuit and only opens and closes the power to the circuit (by connecting the white with red stripe to the solid red)? What am I missing here?

The dimmer switch is actually at the base of the turn signal stalk. The parts that you're showing in your picture are the switch assembly (two switches on one board) that supplies power to the headlight circuit and the running light circuit. Notice in SteveJ's first FSM copy picture that someone wrote in "ground". RB and RW are grounded there, one or the other by the switch at the base of the turn signal stalk.

I've fixed a problem like yours by spraying contact cleaner in to the base of the signal stalk and working the dimmer lever. It gets gummed up if it's not used regularly.

[keith.abergel]

Zed Head, your explanation combined with Steves diagram cleared it all up. I mistakenly thought that the second on position on the switch assembly was used to switch between high/low beam.

Actually, the high/low beams are switched by pushing the turn signal arm outward which switches the high/low beam circuits ground paths. It was this switch that was worn out and stuck in the high beam position even when the turn signal arm was not pushed outward.

Rookie mistake Thanks to everyone for the assistance.

[SteveJ]

The switch is not operated by pushing it outward. It works by pulling it back toward the driver and releasing it after pulling back all of the way. There should be a click when it cycles between high and low.

[rossiz]

funny - i should have piped up earlier, might have saved you some trouble, but thought i was the only one who made that mistake!

i tore apart my whole harness, added extra ground connections at the headlights up front, took apart the entire combi-switch, everything, and when i was upside down under the steering column putting it all back together i accidently bumped the directional lever and VIOLA!! couldn't believe the whole time i kept twisting the right hand part back and forth expecting it to go from low to hi beam...

perhaps i should have read the owners manual that was in the glove box.

welcome to the club my brother