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MG MGB GT V8 Factory Originals Technical - Alternator Question for the experienced

I am about to start conecting the motor to the electrical system. The EFI is now fairly straight forward, thanks to much assistance from people on this site. However I'm concerned about the alternater. I have an 86 range rover alternater which would have to have a much higher amperage than that little MG one. Can I just hook the new alternater up to the MG Loom, or am I going to blow a fuse somewhere. Do I need to change anything else. I remember once hearing something about a Balast resistor (whatever that is).

Any alternator will only deliver the current that is demanded of it by the circuit up to the max output of the alt. So you could put a megawatt alt on a 20 amp circuit and it would only deliver 20 amps, so yes, you can use your Rangie alt without any qualms.

There is a ballast resistor on rubber bumper Bs in the ignition circuit, nothing to do with the alt.
Paul Hunt

Peter, I would increase the guage of the brown lead from the alt. A v8 will draw more current than a 4 cyl.The fans draw about 12 amps ,the EFI pump will draw more than the SU pump. You might want to upgrade the headlamps or add an eyelevel stoplight, fit a CD player.It all adds up.The original lead as fitted to the Rover alt. should be a guide. Barrie E
Barrie Egerton

I think the alternator lead is the tip of the iceberg.

By the time you add a 20 amp aftermarket fan, high energy ignition, the power to run the ECU, the higher demand fuel pump for the EFI, heated O2 sensors, etc you quickly start to go past what the MG fuse block/wiring was designed for.

Tony Barnhill has a section on his webpage about relocating the fuse block. Anyone else have a less radical approach that will get decent reliability out of a basically stock system?


Phil wrote:

"Tony Barnhill has a section on his webpage about relocating the fuse block."

With all due respect to Tony and Ian Pender, imho, using Pender's fuse kit is a complete waste of time and money. All that is gained by it is getting the fuse box out from under the hood and into the car. What is lost is the fact that you now have two extra connections in virtually every circuit in the car, all of the extra connections under the hood. Unless I'm missing something about his kit. If I am, someone please set me straight and I'll apologize.

Getting the fuse box out of the engine compartment is not a bad thing, but leaving it there is not a bad thing either. Adding two extra connections to every circuit is a bad thing. A very bad thing. The most common problem by far with MG electrical systems is bad conections. Adding more is not a good idea.

The best thing you can do, short of a complete rewire, is to go through the entire car and replace connectors - at least clean them well. If the fuse box is really grungy, you might want to replace it as well. You can either use a factory replacement or an aftermarket unit.

The MG does not have an ammeter, which makes it very easy to add loads. MAD sells a power terminal (part # CN-1) for $4.99 that will work very well. Place it in a convenient location, run a heavy jumper from the starter solenoid to the terminal, and you now have a convenient power takeoff point. Or, if you wish, you could buy an aftermarket fuse block with a power input terminal, connect it to the starter solenoid and take off loads from one of the fuses. These blocks are available from many auto parts stores, and are inexpensive.

Naturally, your alternator will have to have the capacity to handle the extra loads.

If you REALLY want to do it right, buy one of the aftermarket wiring kits, such as Painless, Centech, Ron Francis, etc. Or, build your own, using the instructions in the May 2002 newsletter (which I have updated if any one is interested).
Dan Masters

Thank you gentlemen all,
As always, you've come through with the goods. I particularly like Dans approach of running an independent fuse box off the starter, seems to side step alot of potential problems.

There are also 6-way blade-type fuseboxes with the same fixing centres and very similar dimensions as the original 4-way. Factory V8s only used one of the two available output spades on the alt despite the twin electric fans. However I have connected direct from the unused spade to the fan relay, which are only a matter of inches apart, and gained a significant boost in fan speed. As I was able to leave the original brown feed on the relay I now have a 'ring main' arrangement that has boosted the power to other circuits as well.
Paul Hunt

This thread was discussed between 23/10/2002 and 24/10/2002

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