11 replies to this topic

[timmy850]

I bought some C-27H7779 8mm performance leads recently and did the responsible thing and measured all the lead resistances prior to fitting. I originally thought some of them were completely faulty as they didn't give a reading on the 20k setting on my multimeter.. 

 

Coil lead:

5.3k Ohms

 

Spark plug leads:

9.0k Ohms

16.0k Ohms

24.0k Ohms

28.6k Ohms

 

I was a bit disappointed as I was expecting performance leads would at least be under 5k per lead. My current Lumenition leads are about 2k per lead, and an old set of Eagle leads are around 1k per lead

 

 

I contacted the supplier and was told that these are normal values for a new set of leads. It would be nice to know what you're buying before it gets shipped across the world

[Steam]

The best test would be to try each different brand lead with a spark plug out of the engine and assess the spark length, size and colour with each one. That will show the best leads thus best resistance.
Personally I now use spiral wire leads which seem to give the best spark and are 3k ohm per meter which means each lead is 2 to 3k.

[68+86auto]

They don't look like good leads. I do however have some the same on one of my minis and haven't found any issues. The burn voltages and times were all even and good. I have never measured the resistance of any leads.

Edited by 68+86auto, 28 August 2025 - 11:29 AM.

[ACDodd]

There is a reason I stock powerspark components, but people still don’t seem to get it.

Ac

[lsto]

I had this, brand new leads, when tested after watching AC's videos and all were between 15 and 24k. Just binned them and bought powerspark ones. So much stuff we are supplied these days is just junk...

[nicklouse]

Shame NGK no longer make leads. They stated the resistance per meter on them so you could measure and measure to check they were still good.

[68+86auto]

There's a reason those are cheap. Quality terminals alone cost more than that.

[timmy850]

There is a reason I stock powerspark components, but people still don’t seem to get it.

Ac

I have heard you recommend them lots of times but it gets expensive to order single items from one store and ship them to Australia when you have a cart full of items from another supplier

And cost of the components can’t be the only factor in the quality as the price difference between the ones I bought and the powerspark ones is £2. When you can’t check them in person before you buy them, the description of “the highest performance” seems to suggest they’d be decent quality

[Spider]

I wouldn't get too hung up on the values you've measured. Most multimeters use around 5 or 8 volts for measuring resistance, if you were to use a higher voltage, 500 or even 1000 volts, you'll mos likely find much closer to the values you'd expect.

[68+86auto]

I wouldn't get too hung up on the values you've measured. Most multimeters use around 5 or 8 volts for measuring resistance, if you were to use a higher voltage, 500 or even 1000 volts, you'll mos likely find much closer to the values you'd expect.

 

I was thinking about that too.

[gav]

Fit them and retest after a few miles, according to the manufacturer it's common to see unusual results if they are tested before being "fired" for the 1st time. The resistances settle down afterward apparently...

[68+86auto]

Fit them and retest after a few miles, according to the manufacturer it's common to see unusual results if they are tested before being "fired" for the 1st time. The resistances settle down afterward apparently...

 

This I have proven with the same part number leads as Timmy had...

 

As I have said before, I don't normally measure lead resistance but have been doing it recently to prove stuff in posts like this.

 

I just tested a brand new C-27H7779 set and selected the lead with the highest resistance. It had 20k resistance. Now one might think that is bad but that is not the case. A low reading cannot be trusted either as I have seen low resistance leads actually have high resistance on a running engine.

 

I installed the 20k lead on cylinder three. The other leads are all quality leads which all currently measure a low resistance.

 

 IMG_20260709_203022_(1080_x_800_pixel).jpg   52.93K   1 downloads

 

The scope pattern is as perfect as can be. A high resistance would show as a downslope at the start.

 IMG_20260709_203443_(1080_x_800_pixel).jpg   45.53K   0 downloads

 

The voltages are even.

 IMG_20260709_203524_(1080_x_800_pixel).jpg   50K   0 downloads

 

The burn times are all even, well the slight variation is not the lead.

 

 IMG_20260709_203157_(1080_x_800_pixel).jpg   45.41K   0 downloads  IMG_20260709_203229_(1080_x_800_pixel).jpg   38.1K   0 downloads  IMG_20260709_203309_(1080_x_800_pixel).jpg   41.9K   0 downloads  IMG_20260709_203359_(1080_x_800_pixel).jpg   42.53K   1 downloads

 

Now what does the lead measure after running for maybe a minute?

 

3.9k

 

 IMG_20260709_203621_(1080_x_800_pixel).jpg   63.92K   1 downloads

 

So those 20k leads will be perfectly fine. I'm sure many leads have been thrown out because of misleading information going around. There is obviously a slight layer of corrosion which has a path made when exposed to the ignition voltages.

 

Now I do say the resistance doesn't prove much...

 

I recently purchased a different set of leads where the highest resistance was 120k out of the box. Now when it is that high, maybe we can start to think there is a problem. Installing it on the engine did show the downslope indicating high resistance. But here's what will confuse people. After running it on the engine the lead measured 4.9k. Now even though the ignition system created a path, it wasn't sufficient for a running engine but would fool a multimeter. If the lead had a proper connection but read 4.9k, it would run perfectly fine.

 

So measuring the lead resistance can only be used as an indication and should only be done after the leads have been used, even for only a minute.

 

There is a reason automotive scopes were made.

Edited by 68+86auto, 09 July 2026 - 12:33 PM.