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MGB MGB Electrical Question

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kyreb1862

kyreb1862

Jedi Knight
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Mounted beside my CEI ignition box is a resistor. The parts manual calls this a drive resistor. The resistor on my 77 "B" is currently unplugged. What does this resistor do? Do I need to make arrangements to plug it back up? What color wires plug into it? Help!! /ubbthreads/images/graemlins/confused.gif
 
On a stock ignition system, the whole 12 volts goes to the coil when your starting the car... when the key is let back to just on, a relay switches the power to the coil through the resistor, lowering the voltage to around 6 volts. It makes the coil and points last longer. Also called a ballast resistor.
 
Thanks for the info, but I can't get the wiring diagram for the "B" to open. /ubbthreads/images/graemlins/frown.gif
 
Would someone else with a 1977 MGB please take a look at their CEI ignition box. The box is mounted on the passenger side of the engine compartment just above the coil. Standing at the right fender looking down at the CEI box the resistor in question is mounted on the left of the CEI box. It is a long corrugated metal item with spade plugs on each end. Could you please tell me what color the wires are that are plugged into the top and bottom of this resistor. /ubbthreads/images/graemlins/driving.gif
 
Hi John,
This may not help much but, our 79 mgb has the "lucas cei" ignition system. The amplifier is mounted between coil and inner fender, the resistor is a resistor wire incorparated in the loom. Are you sure you do not have the earlier "Lucas Opas" system?
Not much help
Cheers Ric
 
No, it is definitely CEI but, I have read that a lot of the cars with OPUS were changed to CEI. The part in question could just be a left over or it may be something that the DPO just screwed up. After finding that nail in the fuse holder I want to know. I'll take a pic of the part in question and post it tomorrow.
 
Kyreb, the "drive" resistor is separate from the ballast resistor. I had the Opus on my Midget, now replaced with a Pertronix. The ballast resistor is built into the wiring harness, and the drive resistor was a discrete resistor which was part of the electronic ignition. I believe the CEI does not use the drive resistor, so if it's disconnected, I wouldn't worry about it. I left my drive resistor in just so if I ever came by a still-working Opus distributor then I could just plug it in with no rewiring.
 
Thanks for the input sparky. I agree, I think this is just a left over from a change over from OPUS to CEI. I was just wondering because I hate finding unplugged "things" and not knowing what they are. My old TR7 had CEI and I don't remember any such part on it. /ubbthreads/images/graemlins/driving.gif
 
The top wire is White with a green stripe, and the bottom one is solid white.
242339-balast.jpg
 

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Difinitive ballast resistor.

/ubbthreads/images/graemlins/grin.gif
 
Thanks Kenny that is the part. Is it hooked into CEI ignition? My coil currently has 5 wires plugged into it. Is there a possibility that one of those wires should be hooked into this resistor? There is a white wire there that is currently not plugged into anything. /ubbthreads/images/graemlins/driving.gif
 
I'm pretty sure it's just wired into the coil only.
 
[ QUOTE ]
Difinitive ballast resistor.

/ubbthreads/images/graemlins/grin.gif

[/ QUOTE ]

No, that isn't the ballast resistor. That resistor is left over from the Opus module, and should not be connected to anything. The ballast resistor is a resistance wire built into the wiring.
 
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