Dash lights, headlights and main beam

[Icedmunkie]

2 questions here for a 72 Firenza:
1) I've been doing the finishing touches to the electrics but having issues with the dashlights.
Headlights are working fine, power to and from the thermal connector but fuse 4 has no power, nor does J5 back to the awkward switch that randomly makes everything dark for no apparent function or reason at all.

The manual says Fuse 4 is powered from the thermal connector but there are no spare wires or anywhere I can see it connecting too?

Anybody have any ideas?

2) I've fitted relays to the headlights but the wiring to the relays it rather warm, not hot just warmer than I expected it to be. I've taken the feed from the white wires on the bulkhead connector which are now redundant as no coil is being used, this is not warm at all. Any ideas or where have people taken feeds from for relays? Also where would you take it for any additional spotlights?

[droopsnoot]

1 - As I read the diagrams in my Haynes (not sure if you have single or twin headlamps, but they both seem the same) the power goes from B5 (bottom of fuse 1, unswitched battery supply) into the thermal cutout switch, then the other side of the thermal cutout goes to the input of the lighting switch. When you have lights on, the output goes from the other side of the lighting switch into the bottom of H5, where it then provides power to fuse 4. So in that way fuse 4 is powered from the thermal cutout, but via the light switch.

2 - I have relays on both my cars, though they are both newer than yours so maybe things are a little different. I've taken the main power feeds (i.e. the high current line that you're switching to provide power to the lights) from the spare large spade connectors in the cable that runs from the battery positive terminal to the starter motor. In the black plastic block where the cable is fixed to the back of the battery tray, there are four large spades, two (on mine) to the fusible links and two unused.

I can't tell whether the wiring on mine gets all that warm because the fuse and relay board is mounted in the engine bay where it's always pretty warm to start with. The white coil supply wire isn't all that big, though - the original headlamp supply wire that goes through the column stalk is twice the thickness (28/.012 vs. 14/.012 at the coil).

[Icedmunkie]

1 - As I read the diagrams in my Haynes (not sure if you have single or twin headlamps, but they both seem the same) the power goes from B5 (bottom of fuse 1, unswitched battery supply) into the thermal cutout switch, then the other side of the thermal cutout goes to the input of the lighting switch. When you have lights on, the output goes from the other side of the lighting switch into the bottom of H5, where it then provides power to fuse 4. So in that way fuse 4 is powered from the thermal cutout, but via the light switch.

Looking at my wiring diagrams they are the same bar the twin headlight has a some extra wire extensions, which won't affect is issue. That is how I have read it, so my next port of call is to check if the power is getting to H5 and if not trace the wiring back to see why. That makes sense to me. I will have a look later on.

2 - I have relays on both my cars, though they are both newer than yours so maybe things are a little different. I've taken the main power feeds (i.e. the high current line that you're switching to provide power to the lights) from the spare large spade connectors in the cable that runs from the battery positive terminal to the starter motor. In the black plastic block where the cable is fixed to the back of the battery tray, there are four large spades, two (on mine) to the fusible links and two unused.


I can't tell whether the wiring on mine gets all that warm because the fuse and relay board is mounted in the engine bay where it's always pretty warm to start with. The white coil supply wire isn't all that big, though - the original headlamp supply wire that goes through the column stalk is twice the thickness (28/.012 vs. 14/.012 at the coil)

I did think of taking it from there but that then meant to relays were always active rather than switching off when the ignition is taken off, I did think that the thickness might be an issue, so will look at your method and see how that works. I am guessing you have had no issues with the relays being powered permanently? I may need to double-check my wiring, to see see how I can get around this with my relays.

I have noticed that the wiring has been altered on mine to the twin lights so that both sets of lights are on when main and dip are used ie all four lights are dipped and all 4 lights are main. Which I think is not correct, which may explain the extra draw. I have thought of a LED headlight conversion but for four lights it gets quite pricey to do it correctly. .

[droopsnoot]

I haven't noticed any issues with the power being connected to the relay all the time, no. My modern-ish daily driver has that arrangement for the main beams, I think, as they're active on the stalk even when the ignition is off.

As my cars are both snoots, one of the issues I wanted to overcome was that dipped beam just has outer lights lit, and main beam just has inner lights lit (the outers go out). It turns out that wasn't correct on the Firenza with the beefier light switch (that should light all four), but it was correct on the hatch and I just didn't like it. So I had a look around the web and found a suitable diagram, so now I have "normal" lights where the outers come on with dipped, and all four come on with main. If I flash the lights on the stalk, all four will flash. In snoot lights, though, there is only one filament in each light.

I also wanted to have the relay board set up so that if something goes wrong, I can disconnect it and put the lights back onto the original setup, so the switching inputs use connectors that will plug into the existing loom connectors. I then have a separate loom across the front under the nosecone to the nearside lights, with the original still there but not connected up. If the relay board fails for some reason, I just disconnect it and plug the lights back into the standard loom.

Not a difficult circuit (well, not difficult for me as all I had to do was download it), but a fair bit of work considering that I virtually never take the car out after dark.

[1972nail]

An interesting aside, post '76 Magnums and Viva GLS's had the option of round Cibie headlights which had only one filament each and used the same connectors on the back of the lamps as Snoot and Sports Hatch lights. They too only switched on the headlights in pairs just like the Sports Hatch. All 4 were never on at once.

I remember trying to figure out what was wrong on a GLS my late father in law sold second hand to a client and they complained that the headlights were faulty. I think my father in law took it to the Vauxhall dealer in the end who confirmed it was correct.

[Icedmunkie]

I have got everything working of a fashion...

Alternator warning light is not working but if I earth the wire it works but my alternator fitted doesn't seem to allow this function, but that is a seperate issue.

Indicators work, oil light works but main beam works in a very strange way....

When the lights are off the main beam warning light is on but no power to the blue and white wire it is earthed
When the lights are on the same thing but when I flash or put main beam on the light goes out and I get power to the wire. The lights work correctly in the way they are meant to.

The draw from the switch to the relays is still making the wires warm but not hot which I can keep an eye on for now.

Any suggestions, I am thinking an issue with the PCB board possibly.

[droopsnoot]

Do you have a diagram of how the relays are wired? What PCB do you refer to?

[Icedmunkie]

PCB board I mean is behind the dash clocks where the multiway plug goes into.

So I have two relays:
1 for dipped beam
1 for main beam

All four lights come on with main and dipped.
Relays are 40 amp rated with 2x 20 amp poles

Pin 86 - Fed by ignition live from the now unused white wires from coil (this doesn't get warm)
Pin 85 - Earthed to body near the battery
Pin 30 - this is taken from the normal loom (this does get warm)
Pin 87 x 2 - One to R/H side of car and one to L/H side of car.

[Icedmunkie]

Any further information on this at all?

I'm still thinking there is an issue with the clock as lights are wired up correctly but the main beam works the opposite way!

The alternator light comes on if I earth it directly (can't remember if this is right?) but can't seem to get it to work with a 3 wire alternator.

[droopsnoot]

Sorry, I hadn't seen that you'd added the photograph and wiring list.

As I read it, the relays aren't wired correctly. To me, based on looking at some other diagrams on the web, the pins on each relay should be:

Pin 85 - Earth
Pin 86 - the original switch wire, from either dip or main switch, the one that used to go to the lights. This will be a different wire on each relay to split dip and main beam, I think on mine these are the blue/white and blue/red wires.
Pin 30 - the high-current supply wire input, from the battery via a fuse.
Pin 87 - the output to the lights.

So when a voltage is applied to pin 86, pins 30 and 87 are joined to supply higher current to the lights. The lighting switch has to only carry the current required to operate the relay.

Here's one of the diagrams I looked at: http://www.gtsparkplugs.com/headlight-relays.html

And this is another that I looked at to double-check the relay pin assignments: https://www.mgexp.com/article/mgb/headl ... s_revb.pdf