Ignition Coil - How many Ohms?

Moss Motors Tech department shows you how to test your coils Ohm rating.

Category:

Autos & Vehicles

Tags:

• coil
• Ohms
• distributor
• moss
• motors
• British
• cars
• mgb
• mga
• mg
• triumph
• ignition

[Bob144K]

My coil, Moss Motors part no. 143-210 (Q12 Type), is reading 4.3 ohms across the tips of the terminals and 5.8 ohms at the base of the terminals. Is this correct? The coil is new, I bought it several years ago and am just now installing it. I'm not seeing a spark from the secondary wire. Car (1951 MGTD) won't start.

[MossMotorsCom]

The target for these coils was about 3 ohms. The technology was nothing like it is today and mass production allowed for a fair degree of diversity from one unit to another. I grabbed a new one from our warehouse and found it offers 3.7 ohms of resistance across the primary terminals. I'd call that OK. 4.3 ohms is on the high side and 5.8 ohms is almost double the target. My guess is the bases of the terminals you are measuring are a little dirty.

[machinationu]

no fingers

[Arabhacks]

Actually the resistance in manufacture is fairly close from unit to unit when new.

What happens is that they age and resistance changes.

Very much the same is true of all older electronic components.

If an electronic ignition module were built with perts from the past you would need to replace the entire module every 2 years or so!

Capacitors, or condensers as they were known, had a very short life.

Modern electronic parts, including the coil, normally last the life of the vehicle.

[PooPusher007]

@popplewort333 becouse its cold

[peterm3964]

@popplewort333 cause its cold

[Bob144K]

Thanks MM for getting back. I'll clean-up the terminals and try again.  I set-up the bench test for to see if the coil sparks. Will run it today.

[jimnichols001]

if you take your fingers off the metal of the test leads you might get a better reading ... just sayin'

[popplewort333]

Why does the primary and secondary resistance on a ballast coil change when frozen?

[tdskip1]

This is very important if you are running a Pertronix - just a friendly reminder.