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MG MGB Technical - Alternator 18-ACR into a 77 MGB

I'm probably going to need to put a 18-ACR alternator ( 3/8, 3/8, 1/4 connector) into a 77 MGB with the alternator harness connector being different ( 1/4 pointed, 1/2, 1/4).

Questions:
- any reason this can't be done?
- I can obviously get the brown/yellow correct, but are the other two "browns" interchangable?
- in the 77 one brown is a much smaller gauge than the other. If not interchangable, which 3/8's get the smaller gauge?
- any reason to use the harness connector rather than just install individual new connectors?
- would it be easier to install the right rectifer into the 18-ACR?

Thanks for any help you can provide.

Brian
Brian Denis

Brian - I installed an 18ACR in our 66 MGB and did exactly what you propose to do, used single wire connectors (obtained from British Wiring <http://www.britishwiring.com/> The set up works fine. I had to jumper two of the contacts together to get everything to work correctly, but with a 77 MGB the jumpered connections may be made in the existing wiring. If you have problems with no output from the alternator, e-mail me and I'll check what I did to get mine to work, or perhaps Paul Hunt will know which points need to be connected together. Good luck - Dave
David DuBois

The browns go to the two large spades. On my alts in either order as they are strapped together inside the alternator. The brown/yellow to the single smaller (actually the standard size) spade. If you have two small and only one large spade on the alt that would need a bit more investigation.
Paul Hunt

Brian, I have the reverse situation on my 68 GT, I have the 43 amp alternator but had the plug for two 3/8" and one 1/4" spades. I removed the connector and installed individual spades as you suggested. I have the thick brown wire attached to the wide center spade.The other wire is a brown/green from a converted separate regulator and is attached to the outside (toward the fender) spade. My 74 is set up the same way, thick brown attached to the center 3/8" spade and the small brown wire is attached to the 3/8' spade, (the outside spade toward the fender). The 68 has been hooked as I described over three years and everything works as it should, I have never needed to recharge the battery. Be advised the 18ACR may be a little shorter and you may have to shim the mounts with washers to get the the belt and pulleys aligned. You will need to replace the spade on the small brown with a 3/8" terminal. Good luck, Clifton
Clifton Gordon

Thanks David, Paul & Clifton for the comments... but I've dodged this bullet for the time being. I checked the battery ground and alternator connections as you and others had suggested in another post and immediately got great results! Lights, directionals, the full monty!

Interesting alternator harness connector. It's cover protects the connections, but at least on my car the connector is upside down when plugged in... meaning where the wires run into the connector is on top. So crud can run down the wires into the connections, which is what happened to me.

Also, beware of a diagnosis by Autozone on the health of an alternator. I was underwhelmed by the experience of the guy who checked mine. Granted, it's a 27 year old alternator.

I was thinking about installing an alternator I wanted to check and run the car off the battery if necessary to check it's output. Any reason this wouldn't work?

Brian
Brian Denis

Brian, You can check it for operation on the car. Read you battery voltage prior to starting the car for a reference battery voltage. Normally it will be a little over 12 volts. You can check voltage at the brown wires on the fuse box or any other convenient location. With the engine running the voltage should go up to around 14 volt if the alternator is working. Run engine at 1500 to 2000 rpm. The only problem with this test is it doesn't check the alternator under load. Turning the headlights on bright will add some load and you can take another reading. It may be a little lower with lights on. Add the heater motor if you want additional load. Clifton
Clifton Gordon

Thanks Clifton.

My problem would be the different harness connection... which is why I thought I'd have to run off the battery. I wouldn't want to re-wire the alternator connection before I was sure the alternator was good.

But again, I'm in good shape for now. Nice to spend more time driving than working on the car!

Thanks again to you and others for helping me get here!
Brian Denis

Auto Zone, Krugers, Shucks, all of the cut rate auto parts places are NOT a good place to have electrical items tested. One can always look in the yellow pages and find at least 1 auto electric shop in your ares. This is the place to have the items tested. These are the people that know what they are doing. Cheers - Dave
David DuBois

This thread was discussed between 19/07/2004 and 24/07/2004

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