Jump to content

Ballast resistor

Recommended Posts

  • Replies 10
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

i thought I awnsered this last night on another thread


if this is a 3 ohm coil  you find the ON wire which has 12volts ON key position  to + side coil

                                           Find the START wire and put to  + side coil


Personally I would have keep the stock coil/ballast as is most likely Made in Japan. Most new stuff is all China

Edited by banzai510(hainz)
Link to comment

The points are the limiting factor in the stock system. They can only survive a finite amount of current flow. The arcing erodes the contact surfaces. Between 1.5 ohms (coil) and 1.5 ohms (ballast) totals about 3 ohms so the currant flow can be calculated (assuming a maximum 14 volts charge when running) as 4.666 amps. Starting would be bypassing the ballast and with only the 1.5 ohm coil.... 9.3 amps to give a higher output briefly while starting.


Total watts used in the system is 65.33 / 2 = 32.66 watts each for coil and ballast. It would seem the stock 1.5 ohms ballast must be capable of dissipating 32.66 OR MORE watts of heat. 



New coil....

Cannot really have lower resistance or more current will flow not only shortening the life of the points but also over heating the ballast resister' wattage rating. A 'high performance' coil will have to be more efficiently wound and be made of better materials.



The EI Matchbox distributor.

Using transistors to switch the coil on and off and eliminating the points altogether there is no need for a ballast resister to limit voltage and current. Thus a coil can be built with a much lower .75 - 1.0 ohms. The current in a matchbox electronic ignition is simple to calculate as 14 to 18.66 amps assuming a 14 volt charging system. As you can see with over 14 amps as compared to the 4.66 amps of a points system, the matchbox will have a much higher output.  

Link to comment

What's the build date on the driver's door tag say?????? Do you have disc brakes on the front????


You have a '77 right? The '77 is a points distributor. 1.4 ohms is good enough to use with your stock points ballast no need to replace it.

Link to comment
7 hours ago, Lonewolf1990 said:

Just purchased a hot spark coil

Or is it Super stack or Super stockstock Accell ?????? these now made in China. The THe Big Yellow SUPERcoils are the good ones and hase a spare .7 ohm resisitor in the box.


whats wrong with the old coil?????


if you not converting to  EI conversion as HotSpark or Pertronix modules and just useing the points in the distributor i wouldnt do anything.


best improvement would be to convert to a point less ignition so you dont use the points.  just changing to another coil is limited at best or Bad if you but the wrong one in there




Edited by banzai510(hainz)
Link to comment
6 hours ago, datzenmike said:

What's the build date on the driver's door tag say?????? Do you have disc brakes on the front????




'78 was the first year the EI system was used outside of California and front disc brakes. Trucks with build dates from June '77 on, are '78 model years. So it's important to be sure you have a '77 model year. Another clue is do you have disc brakes?

Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

By using this site, you agree to our Terms of Use.