# How does this ignition coil work? Why are there two wires, and where should they be connected?

I'm having ignition problems with my car (1985 Suzuki Samurai). Sometimes the engine will die randomly while driving, and often when warm it will have problem starting.

I bought a new ignition coil, but it didn't work correctly. The new one have all the symptoms of a bad coil (rough idling, poor performance, engine almost dying). So I put the old one back (shown at right in photo below). And now I don't know if the new is defective, or it's because I hooked it up wrong, or maybe it's not getting enough power?

I don't understand quite how the wiring works here, could someone explain? (see photo below)

Why are there 2 wires? (1 and 2). Only number one has 12V when ignition is on? Which should be connected at which point (3 and 4)? On the old one, the two connection points are soldered together...

I have a multimeter - what should the correct voltage be at the vaious points when hooked up?

## 1 Answer

The usual idea is that with 2 wires; one is ignition controlled 12v and goes to the resistor (block on the side with two terminals) so that the coil receives about 9v during normal running.

The other wire is 12v when the starter is operated and is used to feed the coil with 12v so it gets a higher supply voltage during starting - to offset the voltage drop during the starting process.

A quick diagram:

• Thanks for your reply! When ignition is ON, voltage is 9V meassured on the connectors (with wires connected). So that sounds about right. But does it matter which wire is connected to which side of the resistor(?) And I tried meassuring the wire when I turned the key and ran the starter, but it still showed 0V? What you are saying is that one wire should be constant 12V when ignintion is ON, and the other wire should only be 12V when I turn the key to run starter? May 13, 2018 at 12:41
• Yes, if you look, one wire should come from the starter solenoid bringing 12v to over-energise the coil - usually a 9v coil... these systems were to improve the voltage output of the coil before electronic ignition became more common or standard... May 13, 2018 at 13:33