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MG MGB Technical - Coil Question
|I have a coil question. I've had an 80 B for about 2 years. Though it is an '80, it has the Lucas 25D distributor. Does anyone know the NAPA part number for the coil? The car runs, but the coil (since I got the car) leaks a little oily fluid. I wonder it the car will run better with a new coil. Also, can there be a "balast resistor" with this distributor, or was that removed when a previous owner fitted the 25D?|
Your car was built with a wire ballast, that is a length of resistive wire within the wiring loom, which might have been bypassed but is unlikely to have been removed.
I would certainly change the coil as it may deteriorate internally as air replaces the lost oil.
|Ok, so if I have the resistive wire with the "loom" what does it look like, and does that mean I need the 6 volt coil?|
|Oh yeah, I think that my motor is from a '78. EIN tough to read.|
|With a 25D you can run a 12V coil. Tell the guys at Napa that you need one with less than 1 ohm of resistance. That will work well in conjunction with the wire ballast. Most any coil they have would work.|
You can go to any auto parts store and ask for a coil resistor. The common 1 ohm ones are ceramic and are mounted to the fender.
I ran my stock coil without a ballast resistor for a few thousand miles and had no problem. It got too hot to touch though. When I put everything back together a year or so ago, I went to an aftermarket coil and used a ballast resistor. Some aftermarket coils are designed to run with no ballast resistor.
I'm using the cheap Crane electronic ignition system. With a points system, the extra load would burn out the points fairly quickly.
The whole idea of the ballast resistor is to enable a non "resisted" circuit to the coil by a separate lead that is only activated when the starter motor is energized. With a weak battery, the direct wire will produce a hotter spark for starting. Modernly, with better batteries and better ignition systems, the 2 wire system with and without ballast is unnecessary.
The factory fitted ballast resistance wire (on later models at least) is mixed in with all of the other wires in the wiring loom and isn't (to the best of my knowledge) visible without unwrapping the loom.
If memory serves it is pink / white.
Assuming that the wiring hasn't been modified you need a ballasted coil.
|D P Malin|
|If it help to clarify, I check the wiring. There is a SOLID white to the positive terminal of the current coil. For the negative, there are 3 wires; one to the LT of the distributor, and 2 White Black. Does this help to determine if I need a 6 or 12 volt coil?|
These help threads are wonderfull. Thanks All.
|Your wiring has been changed, problem is to figure out how. Originally, there were two White/Light Green wires to the coil+, one is the resistance wire and one is the resistance bypass from the starter solenoid. Just below the fusebox there is a splice sticking out of the main harness; this is a couple of White wires and one with fiberglass braid, which may be White Red, pinK, or browN. The braided wire is the resistance lead; it runs up to the LH headlamp, then changes to W/LG and comes back to the distributor. You need to find out where the new solid White is coming from. If it is coming from a 12V feed, usually at the fusebox or Ign relay just in front of the fusebox, then you need a 12V/3ohm coil. If it is spliced into the W/LG wire, then you need a 6V/1.5ohm coil. You can positively check this by measuring voltage from coil+ to ground with the ignition ON and points CLOSED; if the voltage is 12, then it requires a 12V coil, if voltage is around 6-7, you need the 6V coil.|
Most 6V coils will be marked 6V and/or "for use with an external ballast resistor. Lucas coils for ballast use are marked with a Model number in large type (not the small type 5 digit+ part number like 45290A), which will include a 6 or 7 to indicate voltage. like "15P6"; non-ballast Lucas coils have a 12 in the model designation, typically HA12 for MG applications.
|The current coil is labeled BYS 11p12 (larger numbers) with smaller #'s 453333. Does this help you ID it?|
|That's a 12V coil. Check the voltage as I said to be sure the wiring changes are correct for 12V.|
|Great. I'll post the developments|
|Ok, I put a 12 V coil in and the car seems to run/drive fine. Thank you to everyone who helped!|
This thread was discussed on 03/07/2006
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