Thread: headlight problem - electrical confusion

If you have power on high beam but no light from a known good light then you need to check your earth.

As a bit of a devils advocate, when you say you replaced the connector you didn't reverse the ground and main beam wires?

Just because you have power to the light, to make a circuit it needs to return to the battery (by one means or another), and I have seen some really weird electrical issues caused by bad earths.


Richard

Another vote for Earth problems. The headlight loom has an earth on each site that is a PITA to get too, it is under in the wheel arch.

Also, you have have an earth problem at the relay (if you have them fitted), however as you have a live positive wire at the globe any relay should be working OK.

Test the earth by disconnecting the plug from the globe and check continuity with a multimeter from the black wire to some clean metal on the body.

Ok thanks I'll check the earth.

Flagg I dont understand your suggestion for checking the earth.

Another confusing symptom at the fuse box. I don't have power on the right side of one low beam fuse. Ive swapped fuses around but get the same result, so its not a bad fuse. Maybe I need a new multimeter.

If you're multimeter has a buzzer try the earth on the headlight plug to some bare metal on the motor. If should buzz if it has an earth, otherwise you have a bad earth.

Do you have power on the other side of the fuse? Just make sure when you are testing the fuse you have a good earth otherwise you won't get a reading either.

I would continuity check the fuse, and whilst you have it out check where it plugs into for any contamination (rust etc) as that will stop power from getting out of the fuse.

Do yourself a favour and find a good earth to test from - I suggest extending your meter leads and working from the battery terminal.

Test your voltages back to this point to confirm you have power where you need it.

Then test for continuity (ie the ohms setting on your meter) from this point to the relevant earth connections to make sure you have good earths to your headlights, etc.

It sounds to me like you either have a bad earth some where or you've burnt out a common feed wire.

Two other things - dont assume your fuses are good just coz they have voltage on both sides - remove and test/visually inspect th and don't assume a new globe isn't blown - test it on a known power source.

Hope this helps.

I swapped both fuse and globes over and each worked when fitted elsewhere.

The h4 plug came with wiring ie black for earth, but double checked and looks correct.

I think a bad earth is on the money for why there is power but no light out of high beam. Thanks everyone. Now to find where the problem is.

The low beam still has me stumped. I will unbolt the fuse panel to look behind one night this week.

Yes I do have power on the left side of the fuse but not the right. I have power on the right side of other active fuses.

What sort of Defender/County/Perentie have you got, as I know my new Puma has blade fuses compared to the County which has the old glass ones.

My County with the old glass ones has a fuse (on the radio) that loses connection on the right hand side every 4-6 months. Fuse has power, holder does not. usually spinning the fuse a few times fixes it for a while.

These old glass fuses can become disconnected internally and will intermittently reconnect.

If you have a military rover with black out lights then you may have other issues caused by these. My old ex-army Series 3 got re-wired when the wiring caused me one too many problems, and i never had another electrical issue after that.

If everything else works you may just have a resistive joint (or even the earth). You can test for this with your multimeter on ohms and test between 2 points, both the fuse to the connector on the H4 holder, and, the earth on the H4 holder to your vehicle earth/battery should be zero (or close to) on the lowest setting.

If you need a hand happy to assist, if you want to come for a drive.


Richard

Originally Posted by rar110

I swapped both fuse and globes over and each worked when fitted elsewhere.

The h4 plug came with wiring ie black for earth, but double checked and looks correct.

I think a bad earth is on the money for why there is power but no light out of high beam. Thanks everyone. Now to find where the problem is.

The low beam still has me stumped. I will unbolt the fuse panel to look behind one night this week.

Yes I do have power on the left side of the fuse but not the right. I have power on the right side of other active fuses.

If yours is the same as my 110, your headlight fittings will have 3 wires:

Blue,Pink - LHS Low Beam
Blue,Grey - LHS High Beam
Black - Earth

Blue,Black - RHS Low Beam
Blue,Orange - RHS High Beam
Black - Earth

If your headlights usually only come on with the ignition on, or the engine running then do what needs to be done for them to come on.

Switch your Multimeter to Voltage mode and place one lead on your alternator and the other one on one of the socket clips. It should how a voltage on either low or high beam depending on the position of your headlight switch.

If you turn the multimeter onto Ohms (resistance) or buzzer if it has it and now check the earth wire - it should show very little resistance or make a noise.

If it does not, then check your indicators, because (on my 110 at least) they share an earth with the headlights.

When you say you only have a voltage on one side of the fuse - this is normal with the fuse removed. If you have glass fuses it is not unusual for them to fail or work periodically so replace, and if you have blade fuses then you should be able to see if it has blown but check it with a multimeter anyway to be sure.

If the earth is OK, and they still don't work properly then my guess would be a relay. Physically where that relay is located will depend on where it was installed as I don't think they are a factory fitting.. but you will have to check continuity of it's earth as well, as well as the other wiring and whether it is faulty itself.