280z ‘77 low beam headlights not working.

[240zadmire]

Hello folks,

 

a while back I had issued with low headlights not working and thought the culprit was the battery terminal not firmly secure…. Well, the symptom resurface again.  I made sure all terminal are connected firmly.  High beams work fine but not low beam.  I have the pen test light that connect to a negative and the pen connect to any of the 3 terminal at the head light terminals, seem to have light.  My voltmeter is dead as I the battery is dead 😉

can you explain how do I read the diagram below .

 

do I need to connect the red with black stripe to negative to make the low beams work?

I’m suspect the high beam lever at the steering wheel is faulty 

[SteveJ]

Your suspicions are likely correct. It is probably the switch at the turn signal. It swaps which wire comes into contact with ground. In this case, the switch is not bringing the red/black wire into contact with the ground wire.

[240zadmire]

Well, I took off the multi switches and did a thorough cleaning.  I dismantled everything on the signal blinkers side but to no avail.  I even try to jump the black and one of the red with yellow/white stripe but low beam just won’t work.  Possibly the headlight low beams dead? Strange if they both dead simultaneously .

Fuses are good.  12 volts at the connectors at the headlights.

 

 

any thought?

 

[jfa.series1]

Just as a point of clarification, I am looking at a switch from a '78 right now and the wire colors are different from the FSM diagram. The wires to the beam switch are red/white and red/yellow with black as the ground. If you have not done so already, a continuity test will help diagnose the problem. Touch your ohm meter probes to the black and red/white to check for contact. If none, repeat with the black and red/yellow.  One pair or the other should respond. Pull the switch handle one time to change the beam switch and repeat the ohm test on the pair that did not respond the first time. If you get a response then the problem is not internal to the switch contacts. If no response then the internal contacts probably need attention. With a bit of care, the small phenolic board can be popped out - go slow and easy on prying open the side of the white housing. At least the '77-78 version is more sturdy than the uber-fragile earlier housings!

[240zadmire]

Did the continuity test one red with black stripe against black and red with white stripe against black and has continuity when switching between high/low.

 

I trace the wire diagram and the only missing is the inhibitor.  But isn’t inhibitor is for automatic transmission?

 

the low beam head lights both went bad the same time? I might need to get a new head lamp just for testing?

[SteveJ]

I forgot to ask. Does your car have old style sealed beam headlights, H4 bulbs headlights,  or LED headlights?

[240zadmire]

Yes.  The halogen h4.

 

don’t know if they are related but most of the interior dash light bulbs including the dome light are LED except the fuel empty indicator 

[SteveJ]

Get the to the connector for the high/low beam switch in the steering column. Unplug it. On the dash harness side of the connector, measure resistance from the red/black to the red/ white wires. Report the reading.

Edited September 5, 2021 by SteveJ

[Zed Head]

Unplug this connector, below, turn on the headlight switch and measure voltage at the low beam wire from the main harness side.  The colors should match the wiring diagram.  If you copied the correct diagram for your year it should be red with black stripe.  You didn't say what year car.  If there's no power the problem is between that connector and the lights.  If there is power than the problem is in the switch.

You could even make a fused jumper wire and ground the low beam wire to confirm that low beam will work if grounded.  Or, if you're confident that you have the correct wire just ground it with any old jumper wire.  The headlight will protect the circuit.

[240zadmire]

The year is on the subject line.  It’s ‘77.  I’ll measure it shortly 

stay tune

[Zed Head]

Oops.

[240zadmire]

It’s fixed but I don’t know if what I did actually fix it or by accident…

intraced red/black stripe, red/white stripe and green/black stripe to each connector such as C6 BLACK, C9 WHITE and to the headlamp terminals for continuity …. They all have continuity on those wires.  I believe the ohms for the red stripes were 1.1 and 1.2 ohms respectively.  While I was proving for connectivity test on C9, I accidentally touch other terminal and case a small spark.  That is the only noticeable I made.  Reconnect firmly and seem like both low and high are working as expected.

Still, I have no clue how it is working now.  Last time it wasn’t working because of a loose battery terminal.  Perhaps somewhere, the connectors weren’t firmly connected and/or the ground/earth terminals not firmly secure… I did sand the engine terminal, firewall and one other connector at the AFM just to be sure.  
 

hopefully this the last issue with the headlight…. 
 

btw, I ordered the dapper lighting kit and hopefully they’ll ship in coupe of weeks so that I can upgrade the headlight to be brighter.  So nervous driving at night with the stock headlights

thanks for all the help, as always!

regards