Headlight Gremlins

[PKD]

My 1976 280Z headlights won't  turn on. We had the dash out to work out some other issues when we put it all back, the running lights work, as the turn signals, but there is no headlights. Checked the switch with multimeter and have full voltage at all wires when lights are turned on. The voltage turns off when off. No problems there. High beams don't work either. Checked voltage at high bean wire input at switch and only get 3.5 volts. Checked at Relay, the direct power is at 12+ but the input wire was also at 3.5volts for both high and lows. What did I disconnect or not reconnected properly under dash that could cause this?? They worked shortly after a drive around the block but stopped working the next time we went out for a ride!! Going nuts trying to find problem. Even changed the relays but no change. Checked under grill, pulled the connectors to left and right headlight and had no voltage at front of car. So the problem lies between the switch and the relay. Any ideas?  Has this happened to anyone else that pulled the dash?? What connectors should I check?? I checked everything at the steering wheel.

[Zed Head]

Did you check the dimmer switch?  At the base of the turn signal.  It's a common cause of "no headlights".  It's the ground point for the lights.

[PKD]

20 minutes ago, Zed Head said:

Did you check the dimmer switch?  At the base of the turn signal.  It's a common cause of "no headlights".  It's the ground point for the lights.

How would I go about checking it? I did turn the knob all the way up then down, but to no effect. Does it short out the lights? Is it a wire that hooks up somewhere under the dash or to the light switch?

 

[SteveJ]

Go to the downloads section on this site and get the factory service manual for the 76. There's a link in my signature (provided you're a luddite like me using a computer instead of a smart phone).

Once you have a copy of the FSM, go to page BE-11. It gives a breakout of the headlight circuit.

Instead of measuring random wires, target the circuit. For instance, do you have 12 VDC to ground at each of the headlight fuses when the switch is on?

Also, there is not a relay in the factory wiring for the headlights. Where is it located? What factory wires are connected to it? Is there only 1 relay? Normally there would be 2 for the headlights. 

[Zed Head]

41 minutes ago, PKD said:

How would I go about checking it? I did turn the knob all the way up then down, but to no effect. Does it short out the lights? Is it a wire that hooks up somewhere under the dash or to the light switch?

Steve makes good points.  The wiring diagram in the Body Electrical chapter of the FSM is your best bet.  It shows a little drawing of the dimmer I think as part of the schematic.  And, as he says, there is no relay.  Just wires to the switch then the fuse box, the lights, the dimer, etc.  So that needs figuring.  

Pretty sure that there's a separate specific wire with its own connector for thew ground (not a short) of the headlights.  It would be shown in the schematic.  Maybe it worked loose.

No offense, but you'll have to get up on your electrics terminology.  A "short" mans the electricity got away from the path it was supposed to follow.  Took a short cut.  It's all about proper paths, making the electricity work.

[PKD]

2 minutes ago, SteveJ said:

Also, there is not a relay in the factory wiring for the headlights. Where is it located? What factory wires are connected to it? Is there only 1 relay? Normally there would be 2 for the headlights. 

Nope, not much OEM in this little beastie! The previous owner wanted a track car he could drive to the track. . . pretty unsuccessful due to all what he ripped out. I am re-hooking as I go. The headlights are a little more modern so it required new relays. He took a late model box and installed it in the engine compartment. There are two relays as you supposed. The engine out of a 82 is completely rebuilt with the turbo in mind. The ecm is mega squirt, in which I am trying to interface with given it runs so rich i gag on the carbon monoxide at every light or stop sign.  The drop in power on the input is definitely under dash somewhere between the switch and relay. If the voltage is dropped, would that not indicate some sort of short or reduction of voltage through bad connection?

[Zed Head]

The path.  it's all about the path...

[PKD]

5 minutes ago, Zed Head said:

The path.  it's all about the path...

Yep, thus the question, what could lower voltage between switch and lights. How would the dimmer effect this? Checking the resource Steve mentioned as we speak.

[Zed Head]

All I can say is, yep, follow the path.  Good luck.  

[w3wilkes]

2 hours ago, PKD said:

How would I go about checking it? I did turn the knob all the way up then down, but to no effect. Does it short out the lights? Is it a wire that hooks up somewhere under the dash or to the light switch?

 

I think that he meant the low/high beam switch on the blinker stalk, not the dash light dimmer knob.

[PKD]

2 hours ago, Zed Head said:

Did you check the dimmer switch?  At the base of the turn signal.  It's a common cause of "no headlights".  It's the ground point for the lights.

 

15 minutes ago, w3wilkes said:

I think that he meant the low/high beam switch on the blinker stalk, not the dash light dimmer knob.

Ding ding ding, guess its getting too late for me to comprehend that the reference of "dimmer switch" had another meaning other then a rheostat. I went crazy looking at the path and seeing no correlation between the two circuits. . . duh. OK, to answer that question Zed, yes, that is where I saw the 3.5 volts that followed to the relay with the same results in voltage. This hi/low switch, does it foul(IE needing cleaning) or is it broken and requires replacement? Voltage leading to it is definately 12+volts, going to the head lights is 3.5volts. Path confirmed. Finally, any clue who would have a replacement of this switch, affordably,  if not repairable??

[Zed Head]

It's a switch.  100% to one path, or 100% to another.  They get dirty.  You can take them apart and clean them or just squirt contact cleaner in and work the contacts.