No power on minus side of coil....

No power on minus side of coil....

Joined: September 10th, 2007, 8:05 pm

May 23rd, 2008, 7:05 am #1

Hi All, I went out and try to start my 81 today and there is no power on the minus terminal of the coil. The brown and white wire (from what I can tell) goes from the coil to the fuse box and carries on up to the instrument panel. There is no break in the wire (tested)and no blown fuses. Coil has been tested and said to be Ok. Any suggestions will be greatly appreciated.
Cheers
Jerry
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Joined: June 24th, 2004, 12:00 am

May 23rd, 2008, 10:07 am #2

The brown/white wire goes to your tachometer. There should also be a green wire connected to the -ve terminal, which goes off to the distributor.

You should be testing for 12V (or a bit more ideally) on the +ve terminal, which should have a pink wire connected, along with a black wire going to a capacitor (a little can fixed to the engine lid hinge).

On the -ve terminal, if you have a contact breaker ignition, you should get 12V, 0V, 12V, 0V and so on, together with a HT spark on each drop to 0V, as you turn the engine over. With the engine stationary, it's likely that the contact breaker will be closed, so a random check on the voltage at the -ve terminal will more often than not show 0 volts.

Hope that helps
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Kevin Cozzo
Kevin Cozzo

May 23rd, 2008, 5:46 pm #3

You'd be better off, testing a spark plug off the main coil wire, careful though, can be quite a jolt. Just find some wire and wrap it round the base of an old plug and ground it, and hook the coil wire to the tip of the plug, this bypasses the dizzy cap and the rotor. If you still have points, I'd be lookin at those though, Kevin
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Jerry
Jerry

May 23rd, 2008, 6:23 pm #4

Hi All, I went out and try to start my 81 today and there is no power on the minus terminal of the coil. The brown and white wire (from what I can tell) goes from the coil to the fuse box and carries on up to the instrument panel. There is no break in the wire (tested)and no blown fuses. Coil has been tested and said to be Ok. Any suggestions will be greatly appreciated.
Cheers
Jerry
That was a perfect explanation. Really helps
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Joined: September 10th, 2007, 8:05 pm

May 23rd, 2008, 6:24 pm #5

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Joined: December 21st, 2004, 3:04 am

May 23rd, 2008, 7:26 pm #6


... its 12 volts to the BALLAST RESISTER on the right side of the engine bay (its white and about 4 inches long, mounted to the pod...)

The ballast resister DROPS the 12 volts to something less... usually around 7 - 9 volts to operate the coil.  If you want... you can run a wire DIRECTLY from the battery to the + side of the coil and then see if the engine starts.  (This was/is called HOT WIRING a car, and doesn't necessarily require a key to start the car... just a push.)

It was/is also called an old hot-rodding trick to supposedly get MORE secondary voltage out of the coil by operating it on 12 volts instead of the manufacturer-designed voltage (7-9 volts) and in theory, should work, and does, at least for a while.

I would not be surprized if the coil eventually fails if you leave it this way though...


My best,



Tony
Black Tooth and me... since 1983!
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Joined: August 6th, 2005, 6:03 pm

May 23rd, 2008, 7:32 pm #7

Hi All, I went out and try to start my 81 today and there is no power on the minus terminal of the coil. The brown and white wire (from what I can tell) goes from the coil to the fuse box and carries on up to the instrument panel. There is no break in the wire (tested)and no blown fuses. Coil has been tested and said to be Ok. Any suggestions will be greatly appreciated.
Cheers
Jerry
If the COIL- terminal is always at ground (not +7 or +12) the problem may be in the ignition module.

At rest, both coil terminals should be at the same volatge. To fire a spark, the COIL- is connected to ground, either through the ignition box on the 1500, or through the points on the 1300.

Disconnect the coil and test it with an ohmmeter. If it tests okay, look at the module. I guess the problem could also be with the electronic pickup in the distributor, but I suspect when that fails, the COIL- termianl will stay high and never go to ground.

From the glass lined tanks of old Bertone
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Joined: December 21st, 2004, 3:04 am

May 24th, 2008, 4:25 pm #8


... It was my understanding that when the coil is grounded, current flows in the primary winding and builds up a "charge" as it were, in the secondary.&nbsp; The secondary has not a path to ground because of the gap in the spark plug offers a rather high resistence.

When the points open, or the EIU removes ground from the primary side... the resistence of the gap in the plugs in relatively LESS and therefore an ARC of stored electrons then jumps the gap, and the field collapses via the secondary side of the coil.

Closing the points or the operation of the EIU starts the process all over again.&nbsp; I also understood the term "dwell" to be the time that the points are closed and it refers to the time given in degrees for the coil to recharge its field.

Have I got this wrong?&nbsp; (I'm always learning...)


My best,



Tony
Black Tooth and me... since 1983!
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Joined: October 15th, 2007, 3:50 am

May 24th, 2008, 5:24 pm #9

That was a perfect explanation. Really helps
Don't remember replying to this one..

Or maybe I have become stuck in a few minds from this list.
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Joined: August 7th, 2006, 3:12 pm

May 24th, 2008, 5:35 pm #10

... It was my understanding that when the coil is grounded, current flows in the primary winding and builds up a "charge" as it were, in the secondary.&nbsp; The secondary has not a path to ground because of the gap in the spark plug offers a rather high resistence.

When the points open, or the EIU removes ground from the primary side... the resistence of the gap in the plugs in relatively LESS and therefore an ARC of stored electrons then jumps the gap, and the field collapses via the secondary side of the coil.

Closing the points or the operation of the EIU starts the process all over again.&nbsp; I also understood the term "dwell" to be the time that the points are closed and it refers to the time given in degrees for the coil to recharge its field.

Have I got this wrong?&nbsp; (I'm always learning...)


My best,



Tony
Black Tooth and me... since 1983!
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<img src="http://i46.photobucket.com/albums/f108/ ... gFixed.jpg ";></a>
<font face_"Times Bew Roman" size=1>Disclaimer: This message does not necessarily reflect the views of the sender, or, for that matter, any other carbon-based life form; Any resemblance to actual persons, living or dead, is unintentional and coincidental; All models are 18 years of age or older; Dry clean only, do not use bleach, Tumble dry and remove immediately; Do not bend, fold, staple or mutilate; Anchovies, cheese or jalapenos may be added to orders upon request for an additional charge; Professional driver on a closed course, do not attempt to duplicate; Your actual mileage may vary; No substitutions are allowed; Available for a limited time only while supplies last; Offers are void where prohibited by law; Humor is provided "as is" without any warranties expressed or implied; The user assumes full liabilities and originator is not liable for damages due to use or misuse; We are an equal opportunity employer, with no regard to race, religion, sex, or sexual preference; No shoes, no shirt, no service; Read at your own risk; This post may contain material some may find to be objectionable; Parental advisory: Explicit lyrics; keep away from pets and small children; limit one-per-family please; No money down; No purchase necessary; Ask us about our guns-for-dope trade-in plan; You need not be present to win; Some assembly required; Batteries not included; Action figures sold separately; Contents were packed full at the factory, but may have settled during shipping; Peanuts and peanut products are produced in this establishment and also consumed by the author; Sanitized and sealed for your protection; Do not use if safety seal is broken; Do not use while operating a motor vehicle or heavy equipment; Safety goggles may be required during use; Use gloves when handling; Call before you dig; Use only with proper ventilation; For external use only, if a swelling, redness, rash, or irritation develops, discontinue use; Do not place near a flammable or magnetic source; Keep away from open flames; Avoid inhaling fumes or contact with mucous membranes; Contents under pressure, may explode if incinerated; Smoking may be hazardous to your health; No smoking allowed, except in designated areas; The best safeguard, second only to abstinence, is the use of a good laugh; Text is made from 100% recycled electrons and magnetic particles; No animals were harmed while writing this post; No salt, MSG, preservatives, artificial color or flavor added; If ingested, do not induce vomiting, If symptoms persist, consult a comedian; Ribbed for your pleasure, slippery when wet; Must be 18 to enter; No one under 21 allowed; We check IDs to age 40; Seniors Welcome; Ask for our Senior Menu; Present discount coupons to cashier before totaling; An 18% gratuity will be added to the total for parties of 8 or more; We reserve the right to refuse service to anyone. Return all carts to the store; No dogs allowed, except for the visually impaired; Penalties for early withdrawal, one size fits all; Offer is valid only at participating sites; Prices slightly higher west of the Rockies; Allow four to six weeks for delivery; If defects are found, do not attempt a repair, return to an authorized service center; Please remain seated until the vehicle has come to a complete stop; Objects in the mirror may be closer than they appear; Fasten seat belts; In the unlikely event of a loss of cabin pressure, oxygen masks will fall from above, cover your face first, then assist those around you. Your seat cushion may be used as a floatation device. This disclaimer is invalid in the event of hurricanes, floods, earthquakes, sonic booms, vibration, electromagnetic radiation from nuclear blasts or any other act of war, unauthorized repair, improper installation, misuse, typos, misspelled words, missing or altered signatures, and incidents owing to computer or disk failure, accidental file deletions, and Acts of God. Other restrictions may, or may not apply.</font>
The high voltage at the secondary is generated when the contacts on the primary are opened...

An automotive coil is an inductor (well its really an autotransformer but for this discussion...). When the primary circuit is opened, the field collapses and the voltage at the output can be expresed as V=LdI... V is voltage, L is inductance, dI is rate of change of current...

Hey, Damon is an M.E... (and a very good one)



Jim W. (in the Northeast)
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