Coil How To Tell / Test Which Is Positive / Negative ?

[KTMsm]

Electrics aren't my thing and I've been having a few ignition problems recently

I bought a few aftermarket to coils (for different bikes) some have different sized spade connectors (as OEM) but some don't

How can you tell which is the positive and which is the negative connection or ideally how can you test it ?

The latest one has a black surround on one - my initial thought was black meant negative...

my second thought was the surround was rubber, meaning it's insulated so it's positive

[tricky1962]

The uninsulated connector will be the same polarity as your earth. Therefore, assuming your bike has a negative earth, it will be negative and the insulated tag, positive.

[KTMsm]

Thanks

Is there a way to test which is which - the other coil looks identical but doesn't have the black rubber insulation

I'd assume it's the same design but I'd rather check

Thinking about it if I put a plug in it, off the bike, I should see the spark jump from the centre to the ground electrode, if it's reversed it's wired the wrong way round

Edited by KTMsm on Sunday 6th August 07:29

[Steve Bass]

Nope, doesn't work like that...
The secondary winding is not polarity conscious, it's a simple transformer at the end of the day with a set of High Tension windings that are energised in relation to the alternating current applied to the low tension side ( your connections)...
HT energy cannot go from the block side of the plug to the centre as the HT is not being applied to that side.
Most importantly, it won't damage anything if it's wrong.
HTH

[KTMsm]

Steve Bass said:

Most importantly, it won't damage anything if it's wrong.

That's what I was told - except you lose approx 30% spark energy

But 10 miles after I fitted a new coil - the ECU broke - and stopped sending a signal to that coil

New ECU (and new coil because I wasn't risking it a second time) all's well - which is why I thought I'd better ask more questions

[Steve Bass]

KTMsm said:

That's what I was told - except you lose approx 30% spark energy

But 10 miles after I fitted a new coil - the ECU broke - and stopped sending a signal to that coil

New ECU (and new coil because I wasn't risking it a second time) all's well - which is why I thought I'd better ask more questions

The loss of spark energy isn't down to the direction of the electron flow in the coil winding but the flow through the spark plug centre.
I guess the only risk is whether the LT and HT common side is on the wrong side of the ecu output and that's not protected may have goosed the ecu driver.