Resistance wire in the loom.

[dann01]

It's the one in the loom with the clear insuraltion, and when it goes, it burns this, and the loom tape insulation on the outside, and will allow you car to start, but then immediately die.

Mine blew because I run a 12 volt coil, not a 9 volt, and up until the drive was working fine. But over time, it gets hot, and there you go. So, if you wanna use a 12 volt, this either has to be bypassed, or replaced with non resistant heavy wire.

So, spent yesterday stripping the loom from the dash and investiagting this... You would be forgiven for thinking it was just a few inches long, and crimped into the ignition circute... Yes, it is, but it's about 2 meters long, and goes all over the shop.

Note, the Haynes wiring diagrams are not bad, they do at least explain which wires this thing is patched between.

[droopsnoot]

I got rid of mine on the HPF because it was getting warm. I only noticed because I'd had the dash loom out to repair a historic fault (someone had burned the dash lights wire out) and before I put all the trim back in I ran for a few trips with the loom easily accessible. I asked around, and no-one was really sure whether it should get warm - some referred me to general physics, if you're reducing the voltage the energy has to go somewhere, so it comes out as heat; others just said it shouldn't get warm. It does "meander" quite a bit, as you've noticed - the length of that section is important to produce the correct voltage drop.

So I disconnected the resistance wire from the fuse box, used a switched 12v wire for the coil, and added a cheapo ballast resistor on the coil mounting bracket, where it doesn't matter whether it gets warm as it's bolted to the engine. I've left it all in place because I didn't fancy stripping the loom out, but it doesn't get used now.

I'm surprised yours went because it was a 12v coil, though I always have trouble getting my head around these things. Surely running a 12v coil from a 9v supply will just mean it's not producing as good a spark as it should, as the output voltage is relative to the input?

Trouble is, to be sure you've fixed it, you've got to do a run of the same distance...

[dann01]

Well, it has to be said, the engine sure kicks in a lot stronger on starting now, and having left it running for a while, nothing in the loom, which I have left open where I have spliced and soldered in the new wire, gets hot at all.

As for another long run, I am taking it to the club AGM and national at Beamish the first week end of September. From Somerset, that will be a fair few miles, so that will be the pudding test.

Dan

[MattyE]

Dragging up an old thread here, but I recently bypassed the resistance wire in the loom on my Firenza with good results!
im using 1.5ohm a ballast resistor as i have a standard lumenition system which is optimised for a 3ohm resistance (1.5ohm coil + 1.5ohm ballast resistor) looking at the viva wiring diagrams, the standard resistance wire is 2ohm and thats when new, corrosion and age related deterioration will only increase that resistance further with the end result of lower than optimal coil output voltage...

it took a while of diagram reading and head scratching, but the actual operation is dead easy and took only 30mins tops! ive drawn up a quick ms-paint-tastic diagram to show what i did



end result has been smoother running in general especially from cold starts and less engine 'lugging' when under load! i was suprised that i could actually notice the difference from such a simple change - gotta love free/cheap improvements!!

[droopsnoot]

I'll have to look at mine, I don't remember it being quite so complex when I did it.