How do i test the resister on the firewall?

[m_w]

I think the only untouched component in my engine bay is the resistor on the firewall that works with the ignition coil. Is there a way to verify this is good and working as it should?

[David T]

If the resistor is not cracked it is probably OK. The terminals can rust causing a bad connection. The specs are in the Workshop Manual M:01:04. You can test it with an ohmmeter. The attached file shows the undocumented bypass resistor. It bypasses 1/2 of the ballast resistor during cranking to increase voltage on the ignition coil to improve starting.

[Horsebox]

I just did the same recently and came to the wrong conclusion that the resistors needed changing, as well as the coil. I followed C1 test procedure and my terminal 15 voltage to ground was, and is, around 4.5V. That's out of spec according to C1 test but engine starts and runs fine. New coil and resistor grid and no change at all in all circuit measurements. Agree with Dave T that bad connections are probably the obvious thing to sort before going further and splashing cash.

Do you have a running problem?

[m_w]

I just did the same recently and came to the wrong conclusion that the resistors needed changing, as well as the coil. I followed C1 test procedure and my terminal 15 voltage to ground was, and is, around 4.5V. That's out of spec according to C1 test but engine starts and runs fine. New coil and resistor grid and no change at all in all circuit measurements. Agree with Dave T that bad connections are probably the obvious thing to sort before going further and splashing cash.

Do you have a running problem?

Thanks for the inputs. Ill run through and see what it says.
I have some things out to dmcmw to be replaced, while I'm waiting for that to come back I wanted to test out the items I never have. I haven't been able to get car to idle quite right, so I'm sort of testing everything.

[Bitsyncmaster]

You can test the function of the "bypass" circuit by pulling the white wire off the resistor. Then your car will start but as soon as you release the key, it will stop the engine.

To test that the resistance value is correct you can use an ohm meter. Or if you know the current flowing in the circuit you can measure voltage drop.