Why have two ignition power lines?

[cleverusername]

I have been figuring out my electrics and have managed to get a spark by bypassing everything and wiring it with plug leads and crocodile clips.

Doing this left me puzzled by one of Triumph's design choices. Why have two ignition power feeds, when as far as I cant tell the ignition feeds are all combined at the fuse box and it would equally work as well with one feed?

Was it to allow that to use thinner wiring? Redundancy if one wire failed? Or is there something I am missing?

[Carledo]

If you are looking at the double white wire at the fusebox (1 thick, 1 thin) the thick wire is a feed in from the ignition switch as you would imagine and powers the fused ignition circuits. The THIN wire is a loop out to the dash and powers the tachometer and voltmeter which are not fused. Why they did it this way rather than separating the 2 out somewhere more sensible like out of the column /ign switch plug is beyond me! (though it may be because it's difficult/impossible to get more than 2 wires into one of those Rists pins and there are already 2 in that plug ie fusebox and coil)

There are wiring diagrams in every Haynes manual and many other places. But i've taken entire looms apart and rebuilt them to modern standards and to say that the original design is counterintuitive is a gross understatement. For example, the white "coil" wire from the plug below the ignition switch goes, not to the coil, but to a point near the N/S Strut tower where it joins/turns into the White/pink ballast lead then dives back into the loom, back across the dash and out the O/S to the coil on the O/S bulkhead (Slant engines only, the 1500HL has a different arrangement cos the coil is on the N/S flitch)

Edit, one more thing, the non HL cars (Dolomite 1300, 1500, 1500SE and Toledo) have neither tach nor voltmeter and only have 1 white wire at the fusebox.

HTH Steve

[Richard the old one]

If you have not already my article in the current edition of Dolly Mixture issue 220 April May 2024 may I suggest that you have a read as in the article I cover both the ignition circuit and the starter circuit wiring that is used in the 1500HL. I produced it so that I would know what plugs and sockets were actually used in the circuits and could be a source of bad contacts.

[Carledo]

There is, in my opinion, a distinct shortage of usable ignition live feeds in the standard loom, and most of those that DO exist are too small to carry a useful load, something that caused me to do some deep thinking when wiring up the injection, immobiliser and transmission looms in the Dolomega which alone required some dozen extra ignition lives, a couple of which were fused.

My solution was to draw another unfused ign live feed from the fusebox area (I now have 14 fuses here, instead of the standard 2) which acts as a switching feed for a 40 amp relay that in turn powers a bus bar that feeds the individual circuits. I mounted this on a bespoke panel behind the glovebox that also holds the transmission ECU and a number of other electrical bits like central locking, HRW and electric window relays and the control/reciever unit for the remote locking fob.

My only reservation here, is that a single point of failure exists in the relay itself, to reduce this risk, I used an OE Vauxhall (Bosch/Hella) relay rather than a cheap new one and carry a spare in the glovebox! A bonus to this is that that particular type of relay runs several different other functions in the car, but one size fits all!

Steve

[cleverusername]

It looks like I am not the first to mess around with my loom then because I seem to have ended up with two ignition feeds and a third separate feed to the voltage regulator module for the gauges.

What I would like to do is dedicate one ignition feed, unfused, for the coil and use the other for the rest of the ignition system. It seems like a neater solution, I was just concerned about whether the one feed could take the load. The wiring diagram I have seems to show the two feeds converging at the fusebox.

[Carledo]

It looks like I am not the first to mess around with my loom then because I seem to have ended up with two ignition feeds and a third separate feed to the voltage regulator module for the gauges.

What I would like to do is dedicate one ignition feed, unfused, for the coil and use the other for the rest of the ignition system. It seems like a neater solution, I was just concerned about whether the one feed could take the load. The wiring diagram I have seems to show the two feeds converging at the fusebox.

Feed to the voltage reg (mounted above the fusebox) SHOULD be a green lead off the fused side.

I frequently draw unfused ign live power from the spare tags on the fusebox to operate stuff like EFi, EI, leccy fans and the like and have not, so far, run into overload problems. An ECU doesn't actually draw much current to run it! The only downside is that a moderately intelligent theif could move the ign power lead to a permanent live tag and start the car! Thankfully, most theives aren't that bright!

Which model was your car originally? This affects all sorts of placements in the loom and where some wires end up. Knowing will let me visualize better where stuff is supposed to be and what it does. Then I can take some pics.

I just had a look at a near stock '78 Sprint I have here. The smaller white lead at the fusebox on this car powers near enough everything to do with the engine, including tach, voltmeter, ign light feed, choke light feed (and, I suspect, all the other lights in the warning cluster) and the actual coil feed itself. So it's multi purpose!



This car has Lumenition Optronic, you can see the red lead that powers it off the unfused ign live and how thin it is! Also, what the leads to the voltage stabiliser SHOULD look like. The double dark green is power in from the fused side of the box with a loop out to who knows where and the light green goes to the dials.



Where the ign live for the coil goes in it's travels from the fusebox is a bit moot. But where it ends up is here! Not too easy to see, but dead centre on the pic, 2 wires stick an inch or so out of the loom, one white and one pink joined together in a black insulating cover this is the end of the 12v bit of the coil feed and the beginning of the ballast lead (the pink bit) On other models i've seen, this junction may be anywhere from where it is shown here to out under the bonnet where the heater fan motor wires exit the loom. The other end of the ballast lead is at or near the original coil position. so you can choose to run ballasted or non-ballasted depending on the demands of your chosen system.

PS just blown the pic up and it LOOKS like 2 white wires joined together! But one is actually a light pink colour!

HTH Steve

[cleverusername]

It is 1500HL loom which has been adjusted because stuff on the Sprint is in different locations.

The green wire to the voltage regulator is correct? Explains why the gauges work.

I am basically trying to get things wired so they are reliable. However good Lucas electrics were, after all these years connectors and terminals are beginning to corrode. So the ones which are dodgy are getting replaced.

[Carledo]

Our cousins across the Atlantic call Joe Lucas "The Prince of Darkness" because of the unreliable nature of his products!

Pretty much every electrician over here grumbles about Lucas wiring too.

Honestly, I don't think it's too bad at all, colour coding is accurate and consistent and even after 40-50 years, most things will still work if given a clean up.

I've worked on several 60s and 70s American cars and I can tell you the wiring and electrical parts on those are a shambles compared with Lucas products. Nothing works! Wiper motors NEVER work, guages rarely and alternators and regulators are more likely to be duff than not. Just from a few years sitting in the sun. Yet they complain about our stuff!

Yes the 1500 loom isn't the best one to start with if you are using a Sprint engine, just about every underbonnet wire is in the wrong place!

An utterly simple solution is to draw a 12v feed from the unfused ign side of the fusebox to the coil and run a 12v non ballasted coil, forget the ballast resistor and the wiring complications that go with it and go with the KISS principal! Points or a normal sort of EI unit will be just as happy unballasted (Happier in the EI case)

Steve

[cleverusername]

Our cousins across the Atlantic call Joe Lucas "The Prince of Darkness" because of the unreliable nature of his products!

Pretty much every electrician over here grumbles about Lucas wiring too.

Honestly, I don't think it's too bad at all, colour coding is accurate and consistent and even after 40-50 years, most things will still work if given a clean up.

I've worked on several 60s and 70s American cars and I can tell you the wiring and electrical parts on those are a shambles compared with Lucas products. Nothing works! Wiper motors NEVER work, guages rarely and alternators and regulators are more likely to be duff than not. Just from a few years sitting in the sun. Yet they complain about our stuff!

Yes the 1500 loom isn't the best one to start with if you are using a Sprint engine, just about every underbonnet wire is in the wrong place!

An utterly simple solution is to draw a 12v feed from the unfused ign side of the fusebox to the coil and run a 12v non ballasted coil, forget the ballast resistor and the wiring complications that go with it and go with the KISS principal! Points or a normal sort of EI unit will be just as happy unballasted (Happier in the EI case)

Steve

I've figured out what was going on, the wiring diagram in my manual is wrong. There is only one ignition power feed, a big old fat white wire. The other white wire is not a feed, it actually powers the instruments.

Anyway all is well now. As for using the 1500 loom, it didn't take much modification at all. The battery had to be moved but the only major issue there was a new feed to the starter, which I solved with a heavy duty cable run round the front.

Most things are in pretty much the same place.