Ballast Resistor V12 Etype

(Ian) #1

How hot should the Ballast resistor get , too hot to touch , or is there a problem , asking for a friend with a USA spec V12 2+2

(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #2

They get pretty hot. When new, they typically smoke a bit while burning off
dust or whatnot.

If your friend HAS a ballast resistor, he should consider replacing that Opus
ignition with the later Lucas CEI. Far better and more reliable ignition

– Kirbert

(Ian) #3

Thanks for that Kirbert ,

(andrew honychurch) #4

Just seen this post and it sort of fits my question. I have a XJ12 series one with a SNG Barratt Opus replacement ignition system. I note that it has a ballast resistor but not with a ballasted coil. Does the SNG system remove the need for ballast resistor? My car is losing spark when hot and will not proceed again until its cooled for a while. Must be amplifier, ballast or Coil in my view. Interested in views thx Andrew

(Mike Eck) #5

When it fails, use an ice pack to chill one of those three items and see which one fixes it. That way you’ll know which one to replace.

Mike Eck

New Jersey, USA

'51 XK120 OTS, '62 3.8 MK2 MOD, '72 SIII E-Type 2+2

(Kirbert - author of the Book, former owner of an '83 XJ-S H.E.) #6

IIRC, the SNG Barratt Opus replacement is actually a Lucas CEI in an Opus box. If so, no ballast resistor involved, although there are still resistors in the signal leads to the tach and the EFI – and all of these resistors are in the same resistor pack on the Opus cars. The whole point of the Barratt kit is to provide a reliable ignition system that still looks original, so you’re probably supposed to leave that ballast resistor pack in place.

(John) #7

I think the SNG Barratt ballast resistor is a dummy item. Doesn’t do anything aside from fool the eye. I had this setup on my much lamented 76 XJ12C

( 1971 S3 etype : Ohope beach New Zealand) #8

Hi guys
Here are a couple of pics that may help diagnosis of the Sng system. I found them on the web so E&OE


( #9

I have a series 3 1974 e type and am having a starting problem when the car gets warm after either driving of idling in the garage for 15 plus minutes. I have the Crane ignition system stock Lucas coil and ballast resistor. The white wire leading to the middle pin of=n the 12v side of the BR reads 10.8 volts when the connector is connected to the BR and the ignition is on, not running. The corresponding spade connector reads 12v when the pug is removed from the BR. When the engine is cranking, voltage at the coil is 7.8 and in the on position voltage is about 5. When I run a jumper wire to the coil from the battery, the car immediately fires up and runs very well. When the wire is disconnected, the car will die. I can also run the jumper to the 12v side, white wire connection to the BR and start the car immediately and it runs well. Again this is when the engine is warm. I have not tried Mike’s suggestion of icing each component, the BR, the coil and the module. Just wondering if anyone had any clues in addition.

Jeff Kahler

(Mark Eaton) #10


I think Ed Sowell or Bernie Emden had a write up on the Crane. I am no expert.

The voltage drop you are seeing is either as the result of a high resistance in the wiring, or a higher than normal current draw from the ignition. The fact that the ignition is happy, once the correct voltage is established suggests an unusually high resistance in the feed to the system.

I don’t recall the wiring arrangement now, but I would investigate how power is getting to the ballast resistors. If via a relay, try a new relay or try re-seating the relay. Otherwise there is a connector that is corroded, or partially frayed wire. Might be a very simple fix, once you find it.

My Ser III ran so long as the ignition key was in the start position (ballast bypassed). Once I released it to “run” the engine cut out. That was an open circuit in the ballast. With the E Type, I guess you have the start button. Does it fire, so long as the start button is depressed, but dies once it is released?

Hope that helps.

( #11

Interestingly the car will fie and run sometimes not when cranking but just after I release the key to the run position. This does not happen however when the car is warm and fails to start completely. I am going to get the car into failure mode and cool down the ignition components one at a time with freeze spray: the Crane module, the Lucas coil and the ballast resistor.


(Mark Eaton) #12

Hi Jeff,

So when cranking, there is a relay that should bypass the ballast resistors. If this relay is not working, the ignition is not getting full voltage and is producing weak sparks (if at all).

When you release the key, the battery voltage goes up, the ballast is still in circuit, but the ignition system is now seeing a high enough voltage to produce a spark to fire the engine.

Could just be that when hot the weak spark is not enough to fire the mixture.

If the ignition cuts out when running, that would be something different. But as you have described, it sounds related to the ballast bypass circuit. (The fault is the opposite when the ballast pack goes open - that is, it fires while the starter is engaged, and stops when you release the key).

Good luck.

(Ed Sowell) #13

Mark, I don’t think that’s quite right. In the OE OPUS, with the ignition switch in the Start position +12 is applied to the Start pin on the ballast resistor pack. In the Run position +12 is applied to the SW pin. As seen in the attached pdf, that provides about half the ballast resistance while starting, but not zero.

ballastResistorPackTesting.pdf (64.5 KB)

( #14

I think I have all the possibilities at hand so it is time to do some more educated investigating. At the very least I know that I can get the car to run when it fails to start by simply jumping 12 volts to the coil.


(Ed Sowell) #15

The XR700 system will work with a normal ballast resistor. I believe that’s what Bernie Embden did. Have you checked his website?

As I recall, one came with my system. Probably have it on the shelf, but you could probably get the specs from FAST (current owner of the XR700 brand) and buy one at an auto parts store.