Dead Headlights (1 Viewer)

[B y r o n]

First off I have to say that those of you that are good with electrical, my hats off to you.

Yesterday I took my '73 FJ40 to a friends for dinner, no issues noticed but it was still daylight. When I go to leave, it's dark now, I have no headlights! Every other lighting device is working perfectly. Lucky for me my KC Daylighters got me home after I adjusted them to blind on coming vehicles.

Today I've been trying to track down the source of the issue. Here is what I've done so far:

Checked both fuses and they are good.

Check both headlights and they are good.

Removed, disassembled, cleaned, lubed and reassembled the headlight switch. I did find that the illumination bulb was toast so a replacement will be picked up locally tomorrow.

I have power at the fuse panel on the power side but show no current flowing through the fuse when the light switch is in the run position.

I've tried the dimmer switch in both positions and nothing. I'm not ready to tear into the column to clean and lube it just yet.

I've search a bunch of threads reporting the same issue and the best info so far seems to be a bad ground. One poster mentioned that the headlights grounded to the fender. I've followed the harness from the headlights back to the firewall and can find anywhere the white/black ground wire comes out of the bundle to ground.

If anyone can point me to the spot this happens so I can double check the ground I'd be grateful.

 

[4x4veteran]

If you bypass the dimmer switch will the light work?

 

[Martyt]

I will need to get my headlights and brake lights going when I get my rig back from the shop. A bad ground is a very likely cause of non-functioning electrical components. Coolerman has really good schematics on the FJ40 electrical (my Haynes shop manual has an electrical schematic as well); those should point you to the OEM ground location (not that you have to be wed to maintaining the ground contact point there). I am going to have to do the same thing.

 

[thebigredrocker]

I have power at the fuse panel on the power side but show no current flowing through the fuse when the light switch is in the run position.

The lights fuse should have +12v on both sides even with the light switch off. Maybe try a different fuse.

 

[Fallon 40]

I had a bad dimmer switch.

 

[Tim71FJ40]

Always check grounds. Lots of electrical issues on these is a bad ground.

 

[B y r o n]

The lights fuse should have +12v on both sides even with the light switch off. Maybe try a different fuse.

I found the problem with the 12 volts only on one side. I remember testing with the ground probe to the bolt at the bottom of the fuse block and finding 12 volts. I then moved the positive probe to the right side and moved the ground probe to the left side of the fuse. DAH!

I haven't had time to dig deeper has had to do some work on my mower.

No one can tell me the location of the grounding location for the headlight wiring?

 

[thebigredrocker]

Pretty sure the headlight plugs each have harness WB ground wire. So perhaps they connect in the harness and go to ground at the voltage regulator. I know coolerman told me on my 71 that is the main harness ground.

Yeah I spent most of sunday messing with my riding mower. It’s a triple blade 50” deck. The discharge chute has been prone to clogging since new. While sharpening I had moment. I layed 6 long weld beads at a 45° on the top of each blade just after the leading edge. She slings grass about 10 feet now

 

[BeerM3]

My ‘76s nearest ground to the headlights is on the passenger fender (look for the white wires with black tracer) where the ignition coil is/was. But x2 what others hinted about the dimmer after you’ve checked the easy stuff first. Those steering columns are anything but watertight and mine didn’t work until the old corroded signal assembly was replaced. Unplug the signal plug from the harness and use the wiring diagram to jumper the plug and see if that narrows it down?

 

[cuencanolenny]

I found the problem with the 12 volts only on one side. I remember testing with the ground probe to the bolt at the bottom of the fuse block and finding 12 volts. I then moved the positive probe to the right side and moved the ground probe to the left side of the fuse. DAH!

I haven't had time to dig deeper has had to do some work on my mower.

No one can tell me the location of the grounding location for the headlight wiring?

One thing a person never has to worry about "non original" is grounding. CE Electric in AZ put me on the right track. I have five grounds; 1) Battery to Block, 2) Battery to Frame, 3) Block to Frame, 4) Body to Block, 5) Body to Frame. Another shortcoming of the FJ40, as with many autos, is running the power to the headlights through the headlight switch instead of relays. Right headlight is from the battery, left headlight is from the alternator (my alternator is old style, located low left on the engine).

 

[Marn0]

The High/Low beam switch on the steering colum is where i had trouble with mine. Dirty contacts. A little hit with some fine emery paper to both sides of the contacts and a blast with contact cleaner and they were good as new!

 

[pbgbottle]

I can’t remember what my exact issue ended up being but I lost my headlights one night also. And eventually my last hope I jumped a short wire direct from battery to the one headlight I figured one was better then none. And bam all my lights lit up both headlights and all side marker lights also. I was able to head for home and had no issues. Obviously I still had an issue to fix. But his may be another option to find your way home with just one headlight direct to battery in emergency situation .

 

[Martyt]

One thing a person never has to worry about "non original" is grounding. CE Electric in AZ put me on the right track. I have five grounds; 1) Battery to Block, 2) Battery to Frame, 3) Block to Frame, 4) Body to Block, 5) Body to Frame. Another shortcoming of the FJ40, as with many autos, is running the power to the headlights through the headlight switch instead of relays. Right headlight is from the battery, left headlight is from the alternator (my alternator is old style, located low left on the engine).

Exactly. It is just a ground— find the best solid ground is the key— if you are worried about OEM ground then run a false wire to that location. If OEM ground is the fender then, in my view, that really is not the best location from a negative standpoint (even if OEM). As I said before, and as others have said, bad ground is usually the issue— not always of course but the first place I would look.

 

[4x4veteran]

Grounds is funny animals.
First learned about the strange things that happen with grounds was with my dad's 57 Ford pickup when I was about 16.
Every once in a while when the door was opened and the dome light came on the horn would honk.
Electricity takes the path of least resistance so the dome ground was bad and it found it's way through the horn ground.
When I was first out of the service I briefly worked at a gas station/garage.
I got the reputation as the electrical wiz kid because when customer would come in with a tail light that was out they would sell a new bulb and couldn't figure out why it didn't work I would simply clean the ground and the light would work.
I got my TLC in 73 and about three years after that started traveling to art shows to peddle my wares.
I was doing a lot of night driving and was having problems with fuses blowing and trouble with head lights and running lights on the Toy and my trailer.
In spite of my genius, I took me a while to come to the conclusion that grounding was the problem.
I gave all the connections a good cleaning and had no problems for many years until one day my head lights wouldn't work.
I right away thought grounds.
Dug in and started checking and cleaning.
Turned out to be the dimmer switch was shot.
Everything was going smooth electrically until three or four years ago when my dash lights would come on when the brakes were applied.
If you guessed grounds you are right.
It wasn't until a short time ago when I had a little ambition that I finally put some relays in for the lights.

 

[cuencanolenny]

You will find this link in many places on mud, here it is again. Daniel Stern Lighting Consultancy and Supply

 

[cuencanolenny]

You will find this link in many places on mud, here it is again. Daniel Stern Lighting Consultancy and Supply

And this is a good place to get quality cables, military style battery post clamps which are sized differently for positive/negative and the covers for them. CE Auto Electric Supply – Automotive Electrical Solutions

 

[73tlcv8]

my 73 only has one headlight fuse iirc. Anyway, the failure modes for me were a corroded faston style connector on the rear of the fuse block, and a bad fuse that looked good. I assume the poor connection of the connector melted the solder in the fuse end cap leaving the fuse element in tact. It looks good but tests bad.

 

[B y r o n]

Well I appreciate everyone's comments and advise.

I took a few minutes today and tried to run a separate ground to one of the headlights hoping that power was getting to them. No such luck so it looks like I'm tearing into the dimmer switch since that is the only place I have not looked.

 

[cuencanolenny]

Is your dimmer on the floor? Pretty universal in my experience. If not, groan.

 

[B y r o n]

Is your dimmer on the floor? Pretty universal in my experience. If not, groan.

Dimmer on the '73 is on the column, turn signal combination.