GQ Patrol Head Lights Won't switch on

I have a problem I hope someone can help me solve.
The headlights won't switch on, so I bought a replacement Combination switch which made no difference. (Still not working) I have checked all fuses and they are good and there is electrical continuity between the switch and the light circuit at the light socket. I have checked all relays and fuses in the light circuit but still they won't switch on from the combination switch control.
I have wired up a temporary switch that injects 12v directly into the light circuit from a SPST switch knowing that the lights are negatively ( - ) switched from the cars circuit. This setup gives me headlights now but should not be the long term fix for the problem, the only thing I haven't done is replace the relay tucked up near the firewall right hand side. (Drivers side) When injecting 12v directly into this line the relay clicks ok but not when using the proper headlight switch.
Logic tells me this is probably what the cause of the problem is so that's next on the replacement list.

I just had a thought, I will check the negative contact at the relay but right now it's raining heavily so it will wait.

Has anyone had this problem and found a FIX?

Thanks in advance.
Bernie

When you checked the 2 headlight fuses in the fuse box inside the vehicle did they both have power?

If not, there's a main fusible link out near the battery for the headlights. Check that it's not blown or has a bad connection caused by corrosion.

There is no factory fitted head light relay and the headlights are positively switched.

Like I said in my original post I checked all fuses and they all work, but there are no in-cab fuses for the headlights in my model of Patrol it has Rear demisters fuses at the indicated panel position instead.

I have checked the Fuseable links next to the main battery as well and they are all working, but the Head Light Fuseable link is at Earth potential which indicates that the circuit is Negatively switched and not Positively. Also the High beam relay (blue) will not switch (Click) from the Combination switch on the steering column until I switch my temporary light switch on that puts 12v into the wiring harness, that's when the relay works ok.
Next to that blue relay is a small box and they both mount to the inside of mud guard RHS of the engine bay close to the fire wall, I'm not sure what this box is for.
The High beam relay switches at Earth on as well.
There is possibly a bad earth somewhere in the system, but finding it is proving difficult and I'm just clutching at straws at the moment anyway so I have arranged to talk to a Nissan Tech on Monday and see what he thinks, if I get anywhere I will post my progress here.

Just so you all know the vehicle model, it's a 1996 GQ Y60, 30th Anniversary model 4.2 Diesel

Thanks for your input and suggestions.

I thought it should be 12v Positively switched as well but why would the Fuseable Link circuit be at full Earth potential? Unless there is a short to Earth.
There was no gradual flickering and fail in the lights it was lights out instantaneously which makes me think Fuse too but where is the fuse, and why is the circuit complete but not working?
I'll wait and see what the Technician says.

just note i have had 5 new combo switches that didn't work from the box. took em back ended up using a floor switch. (had a different prob in my laser)

How did you check the fuses. I hear it all the time "yeah I checked the fuses and there all fine". Normally when they recheck them they find a blown one.

Use a test light and check on both sides of the fuses. The headlight fuses are the two bottom fuses on the LHS column. They should be 15amp fuse.

Once again do you have power at these fuses?, with the headlights switched on. It is common for the fuse holder to melt and a common fix is to put either an inline fuse or circuit breaker normally mounted near the 3 blue relays beside the fuse box.

The blue relay out under the bonnet could possible be for spot lights if fitted or someone could have added to the high beam.

Your multimeter will pick up an earth potential through the bulbs. If the fusible link is connected to the positive battery post how can it be negatively switched?

You problem can't be an earth problem if you connect 12 volts positive and the lights work.

Going by what you have posted so far you either have a blown fusible link or a bad connection at the fusible link.

What Yendor said... if the Headlamp Fusible link is at earth then it is knackered.
You can't have +12 volts on one side and earth on the other of a fusible link.

Best way to fault find in a low resistance circuit like lighting is with a test lamp.
If it lights one side of the link and not the other then thats the issue.
Ditto the fuses, then the combination switch then the headlamp plug

The "blue relay on the firewall" is aftermarket if it is anything to do with the headlamps.
Many people will put relays in the lighting circuit to give more power to the bulbs and save the combination lamp.
It may also have been for aux lighting

Thanks guys for your input, the problem is solved. Woohoo!

I had gone through all the difficult stuff only to find that it was simply a poor connection at the Positive terminal on the battery, one of the electrical sockets that feed out of the battery had a bad circuit. (Open Circuit in fact) After I went to the auto electrician and told him I had a bad connection at the battery that I had to sometimes tap to get ignition he started there and found the fault.

One of those DOH! moments.

All working now and I'm doing a wire clean up over the next few days to make sure everything else is in good condition.


Cheers