coil wiring

    I checked the voltage to my coil today and got 5.6 volts with the ignition on.

    When I turned the key to crank the starter the voltage stayed around 5.6 volts. Is this normal ?

    1. Should I get a full 12 volts at the coil when the motor is being cranked ?.

    2.I dont see a pink wire going to the coil, I have a red wire with a green trace that goes from the coil into the firewall plug.

    Nothing is cut or spliced.

    3. What happens on the interior side of the firewall, is the pink wire inside the car ?

    Thanks

    Quote from cobraboy

    I checked the voltage to my coil today and got 5.6 volts with the ignition on.

    When I turned the key to crank the starter the voltage stayed around 5.6 volts. Is this normal ?

    No.

    Quote from cobraboy

    1. Should I get a full 12 volts at the coil when the motor is being cranked ?.

    Yes. It comes from the rear small terminal of your starting solenoid.

    Quote from cobraboy

    2.I dont see a pink wire going to the coil, I have a red wire with a green trace that goes from the coil into the firewall plug.

    Nothing is cut or spliced.

    The pink resistance wire is part of the under the dash wiring harness, from the plug to the ignition switch "run" terminal.

    Quote from cobraboy

    3. What happens on the interior side of the firewall, is the pink wire inside the car ?

    See above.

    Quote

    Thanks

    Check the rear small push-on terminal on the solenoid for 12V while the ignition key is in start. The wire color is brown and it is spliced to the coil lead, red-green stripe, at the firewall connector. You may want to disconnect the large cable to the starter while troubleshooting the coil voltage problem.

    There are a special contacts inside the solenoid with a braided copper lead that provides the 12V during start. The copper lead brakes from old age (don't we all) and the contacts get burnt. It is a replace only.

    Jim

    Thanks Jim

    I will do some checking tomorrow.

    I think I know why I did not the 12v when cranking as I pulled the rear thin wire on the solenoid to stop the starter when I did the voltage test, so that probably explains that one as I did not realise it would also be supplying the coil 12v.

    If I am only getting a low voltage at the coil does it mean that the pink wire has gone bad ? do they do that ?

    Thanks

    Mark

    It's a resistance wire, probably made from carbon impregnated thread and not one made of copper. Over time they do fail but not often. Replacing that one wire is not easy as it is molded into the firewall connector. And I think the nominal voltage at the coil should be closer to 9 volts too.

    Jim

    Have done some checking today.

    Found the pink wire. Feed comes from my ignition switch to a plug under the dash, the rally pac tach then plugs into this then the pink wire plugs into the other lead coming out of the tach and goes to the firewall plug.

    I have 12v going into and out of the tach.

    If I pull the coil feed wire and connect a meter between it and earth I have full 12v.

    If I put a meter across both coil posts with both wires on I have 5.5 - 6v.

    If I do this with the engine running I only see 4-5v.

    I have 10v across the coil posts when the motor is being cranked.

    I have tried 2 coils the readings are the same.

    I am no auto electrician so please tell me what I am missing. As Jim says I should be seeing 8-9v across the coil.

    Thanks

    Dave

    I remember when I first got the car I was concerned that according to the label on the coil it was a 12v coil not intended to be ballasted. So I bought a coil designed to be ballasted and did some checks at the time to determine whether the wiring was stock or not and never really got to the bottom of it.

    So I am re visiting the issue and thanks to Jims tips I have found that I still have the proper set up but am confused as to why the voltage at the coil is so low.

    To answer your question yes the car starts and runs, but ever since I have owned it trying to get a smooth idle has been tricky, I have been wondering if the coil is getting enough volts.

    I seem to be a couple of volts adrift at the coil with the ignition on and also when cranking and even more volts adrift when running.

    Battery voltage = 12.8v

    Rear solenoid terminal when cranking = 11.7v

    Voltage across coil when cranking = @ 10v

    Voltage across coil with ign on = 5.5 - 6v

    Voltage across coil with engine running 4 - 5v

    Mark

    Edited once, last by cobraboy (June 13, 2010 at 12:42 PM).

    Low voltage is sometimes the result of corroded contacts. I know, something you really wanted to hear. Another possibility is a "pinched" wire. That being said, take a measurement from the positive terminal of the battery to the positive terminal of the coil - not to ground. This will give you the voltage drop. Do a reading at start and at run. Start should be zero, run should be about 5 to 7 volts. What is the run voltage at the battery? That should be about 14 volts.

    Jim


    I have parted and cleaned all electrical connections in the engine bay and coated them all with petroleum jelly.

    The firewall plugs are in very good order with no corrosion on pins or sleeves.

    So am I OK with these readings

    Thanks Jim

    Mark

    Edited once, last by cobraboy (June 13, 2010 at 4:52 PM).

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