HEADLIGHT ISSUES

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Online GEOFF289

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HEADLIGHT ISSUES
« on: January 17, 2023, 03:22:56 pm »
Here's one for the sparkies. I'm stumped for not just a fix but to understand how this problem can possibly be happening.

Before this story starts everything worked fine in the lighting department in my '66 coupe, except for the dash lights which were pretty faint. I virtually never drive it at night so this has not been a priority but on last year's club trip to Tassie this issue was a bit annoying as we got off and on the boat in Devonport in the dark. With this year's trip coming up I thought I'd address this and install some LED dash lights.

That all went fine apart from some scratched hands fiddling around behind the dash and I thought I'd install a new headlight switch while I was at it. I wisely decided to test it all before buttoning it up again. Dash lights are great, enormous improvement, the rheostat in the switch works nicely adjusting the brightness of the dash lights - but no headlights!

Weird!. I have dash lights, I have tail, stop, parkers and indicators, but no headlights. I have a relay kit in the headlight wiring so the full current isn't going through the switch, maybe the fuse in the relay kit has blown for some reason so I check that but its fine.

Then I checked whether I had high beam. Sure enough, that's fine. Here's where it gets strange. When I hit the dipswitch again the high beam indicator goes off as it should but the lights stay on and as far as I can see they are still on high beam (bit hard to be absolutely sure without risking blindness). Turn the lights off at the switch and then back on. Nothing. Hit the dipswitch and on they come on high beam. hit the dipswitch again and they stay on but indicator goes out.

So I put the old headlight switch back in and test - exactly the same result. Note that this problem didn't exist before I started this project. I know this because as well as the dim dash lights the headlights were seriously out of alignment and I had been adjusting them in preparation for Tassie a couple of weeks earlier. Put the new switch back in and still the same.

So now I think maybe the dipswitch has developed a quite coincidental problem and ordered a new one. Until I could get that I tried bridging the terminals on the plug that connects to it and taking it out of the equation. This reproduced the same problem, indicating to my electrically challenged brain that neither the headlight switch or the dipswitch is the problem, but I put the new dipswitch in anyway and still have the issue.

So can anyone explain this? It makes no sense to me. Even the possibility that the LED bulbs are interfering with something doesn't seem to me to explain what its doing. I could test this by removing them and putting the old incandescent bulbs back in I guess but would rather avoid the hassle.

As things stand at the moment I could drive it at night by turning on the lights and hitting the dipswitch twice but I'm pretty sure I'd be stuck on high beam. If necessary I can adjust the lights down as far as I can  to avoid blinding other drivers and it'll probably be OK for the short night time driving in Tas in a month but I'd really rather both understand and solve the problem properly.

Offline pmb0186

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Re: HEADLIGHT ISSUES
« Reply #1 on: January 17, 2023, 10:29:33 pm »
You have a wiring error in you headlight relay kit
Get your multimeter out and schematic and follow it through.
You have inadvertently built a latching circuit


 
does anyone remember laughter

Online GEOFF289

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Re: HEADLIGHT ISSUES
« Reply #2 on: January 18, 2023, 07:53:33 am »
Well OK, but this is a plug and play relay kit that has been in the car for years without this problem. It's probably this one, certainly got it from CM.

https://www.custommustangs.com.au/headlight-relay-harness-dual-40a-relays-30a-fuse-2

This weird issue has only arisen when the new LED dash lights went in. From what I posted above you can see that the neither the new headlight switch nor the new dipswitch are involved as the old headlight switch produces the same result and taking the dipswitch out of the equation altogether and bridging the terminals on its plug also produces the same result.
« Last Edit: January 18, 2023, 08:47:25 am by GEOFF289 »

Online GEOFF289

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Re: HEADLIGHT ISSUES
« Reply #3 on: January 18, 2023, 03:47:49 pm »
Further to the above, I would say pmb0186 is correct about the issue being in the relay kit. Today I've taken it out of the equation and plugged (one of) the headlights back into the original car wiring and everything works as it should again.

What I can't understand is why the relay kit has suddenly gone bad like this. All was fine just after Christmas when I was fiddling around with the headlight alignment and the only thing that's changed since then is the LED dash lights going in. Since they are on a completely separate circuit from the headlight switch to the headlights themselves I'm damned if I can see how they could cause this. I can only think its just some inexplicable coincidence.

I did the google short course on latch circuits. I think I sort of get the overall concept but most of it was way over my head.

I think I'll just get a replacement relay kit and write it off to experience.

Offline pmb0186

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Re: HEADLIGHT ISSUES
« Reply #4 on: January 18, 2023, 07:21:49 pm »
I can’t see how what you are seeing would be caused by a fail relay
Had a look at the kit and if plug and play why don’t you remove it for testing
If it is the kit the headlights will function correctly when removed
does anyone remember laughter

Online GEOFF289

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Re: HEADLIGHT ISSUES
« Reply #5 on: January 18, 2023, 07:44:41 pm »
I can’t see how what you are seeing would be caused by a fail relay
Had a look at the kit and if plug and play why don’t you remove it for testing
If it is the kit the headlights will function correctly when removed

And they do.

Online SMH00N

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Re: HEADLIGHT ISSUES
« Reply #6 on: January 19, 2023, 08:31:11 am »
So if you remove the relay kit and you have both headlight circuits, something has failed. Change the relay, check the wiring hasn't been exposed somehow when you were working, use your multimeter to check what headlight circuit comes on when you hit high beam, or is on normally. Have you thought you may have actually blown both low beam filaments at the same time? That's pretty desperate, but I been there where you are now too so desperate men do desperate things :)

One random thought I have - I put LED dash lights in I sourced from Jaycar. These had a polarity, and if put in backwards they wouldn't work. Didn't affect anything I could tell, 'cept they didn't light up. Perhaps something is inter-related?

Online GEOFF289

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Re: HEADLIGHT ISSUES
« Reply #7 on: January 19, 2023, 08:54:21 am »
Thanks Stephen.
 
It does look like its an issue with the relay kit and must be just coincidence its failed now. The low beam filament in the one light I plugged back into the original car wiring is fine. Even with both of those blown I don't see how the high beam would light up in both dipswitch positions. In the low beam position it should just be directing power to a blown bulb.

The LED kit instructions mentioned the possibility of polarity issues but I just plugged them in quite randomly and they work perfectly so don't think that's an issue.

The whole thing is weird. Today I'm going to just check the earthing of the relay kit, given that weird electrical things in these old girls are often down to earthing. If I find nothing amiss there I'll just get a new relay kit and write it off to experience.

Online GEOFF289

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Re: HEADLIGHT ISSUES
« Reply #8 on: January 21, 2023, 03:17:57 pm »
I laid the relay kit out on the bench this morning and bench tested it by applying power to the relay trigger wire and the power in terminal on the plug that connects to the car's original wiring and testing with a multi meter.

This pretty much replicated the mysterious behaviour when it was in the car so I think we can conclude the relay kit has developed a fault and its just coincidence its chosen now to do it.

For the time being I've just returned the lights to how it left the factory until I can get a replacement relay kit and be bothered to install it. As I said at the beginning I hardly ever drive it in the dark and then only for pretty short distances so I'm not too fussed about that.

Offline 66FBK

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Re: HEADLIGHT ISSUES
« Reply #9 on: Today at 01:05:31 pm »
I am a Technician and sometime I am stumped by fairly basic electrical gremlins you can get in car electrics. Most come back to bad earths but when you start introducing new devices such as relays and LED lights , then things really get interesting. I chased crazy electrical symptoms years back after and engine swap like lights flickering, radio noise, random starting issues  and sparking gear lever ( yes sparks) until I realised I had not connected the engine earth strap. You will often see one headlight with both high and low beams glowing orange. That is a bad earth or -ve to the light. I added a relay for the electronic ignition to my early XP Ford after realising it was only get 10v to the coil via the resister wire. This worked well until it would not turn off after the key was turned off. A bit like your head lights. After a lot of head scratching I found the Alternator light in the dash was somehow holding the relay up and keeping the engine running. Because I changed the load on the ignition cct the small 5w bulb was enough to hold the relay up. I put a dummy load resistor on the ignition wire and problem solved. By changing the load of the dash lights or by introducing a diode into the system with a relay, strange things can happen. I hope this helps.
Dave
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Online GEOFF289

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Re: HEADLIGHT ISSUES
« Reply #10 on: Today at 05:02:49 pm »
Thanks for all that.

Although this one seems more inexplicable than most, I'm no longer surprised at the electrical surprises these old girls can provide. Your story about using a relay to address the resistor in the ignition circuit is interesting. When I was sorting out the new engine in mine I had to ensure a full 12 volt supply to the coil and my first idea was a relay triggered by the resistance wire but someone advised against this but I can't remember why. I ran a new resistance free wire from the ignition switch instead. Haven't had any problems on that front.

As I said above, I have bench tested the relay kit out of the car and it seems to misbehave in the same way it did in the car so I think its failed somehow and its just coincidence that it became apparent when I put the LED dash lights in. It could be a year since I turned the headlights on so the relay kit may have failed some time ago.

Anyway, I did put the lights on going through the tunnels on Australia Day and they worked fine with the original car wiring. I haven't got around to getting a new relay kit yet.

Thanks again.