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Posted: Fri Mar 16, 2018 7:52 pm
by 1970 cortina GT
Here is something I’m going off just not sure on the ‘big’ connection on the top left of the picture, this is the connection to the starter solenoid? adamB hello and :welcome:

How to convert from a Generator to an Alternator.

Submitted by Nomad, 26th July 2005

NOTE: This guide is written for a vehicle that is fitted with a generator and is POSITIVE earth. The procedure outlined below will convert the vehicle to negative earth.

It's not a difficult conversion. About the easiest one to use mechanically is the Lucas self regulated alternator off the Escort 1600, that way you get all the necessary brackets and stuff.

Identify where the idiot light terminal is and whether you have one or two main power terminals. If you have two they will probably need to be shorted together to get an output.

Disconnect and remove the battery and do the mechanical installation.

Disconnect and remove the voltage regulator. There will then be two BIG wires and two small wires. Join the big wires to each other and insulate them (solder and shrink tube is good), then join the two little wires and insulate them, the short black wire is the old regulator body earth which may be discarded.

Down at the alternator this will give you a BIG wire and a little wire, the BIG wire goes to the main power output terminal and the little wire to the idiot light terminal.

Reverse the connections at the coil.

Reverse the connections at your gauges.

If you have a radio that works with a positive earth, disconnect it and isolate the power lead to the radio.

Reinstall the battery and wire the positive terminal to the Starter solenoid terminal and the negative to the body earth.

You are finished.

please find the document in the 'how to' section

Posted: Sat Mar 17, 2018 12:20 pm
by Brett Wilkie
Are you speaking of the large connection on the alternator? If yes, that should go to your starter solenoid connection, the same pin that the battery cable is connected to. The idea is that the alternator output is going to the battery Pos.+

Posted: Sat Mar 17, 2018 12:52 pm
by 1970 cortina GT
Yep that’s the one I meant, perfect, thanks.

Posted: Sat Mar 17, 2018 10:45 pm
by Brett Wilkie
I don't know what your alternator puts out so be sure that the gauge of your wire is sufficiently thick to handle the load. I actually like the idea of the alternator you are using, if for some reason my current setup fails I will change over to what you have.

Posted: Sun Mar 18, 2018 8:33 am
by 1970 cortina GT
You read my mind, cable size was my next question. Thanks.

Posted: Sun Mar 18, 2018 12:28 pm
by Brett Wilkie
There are wire gauge calculators on line that are easy to use, this for example.
These are handy if you are doing something like putting your battery in the trunk and have to calculate for those long runs. I your case I guess you will be only going about two feet to the starter motor. I don't know for sure but when I put your alternator ID number on line it comes up with a 40Amp output?? ... 8504-6220/
I like to error on the side of caution so I calculated 60Amp output and 2 feet of wiring. You can see that 10 gauge wire should be fine with little voltage drop. Just ask for 10 gauge wiring and get some good connectors for each end and all should be well. Here is an example of the calculation.


Posted: Sun Mar 18, 2018 5:25 pm
by 1970 cortina GT
Thanks Brett, that job completed, thanks for all the advice. Next wiring issue is hooking up my Petronix ignition to the coil etc. I notice on my drawing that there is a contact breaker from the coil, any idea where that is and what it looks like? Getting closer to lift off........Image

Posted: Sun Mar 18, 2018 9:55 pm
by Brett Wilkie
You are replacing those contact breakers inside your distributor, what Pertronix kit did you get and what distributor are you using. I am assuming a Lucas type?
Have a look at this video.

Posted: Mon Mar 19, 2018 7:54 am
by 1970 cortina GT
Of course it's the points, don't know why I didn't get that.......... I have an ignitor 11 with the Petronix distributor. I'm assuming it's all working, guess I'll find out. I also have the original distributor just incase it doesn't work. Good demo by the way.

Posted: Thu May 03, 2018 9:21 pm
by 1970 cortina GT
Old topic but one more question to pose. So I managed to fire up the twin cam but I have a problem with the alternator getting warm and the battery draining. I found that the switched , thick brown and yellow wire on the alternator is always live, 12 volts. I followed the previous instructions for getting rid of the voltage regulator but something is still wrong. Any advice would be gratefully received.

Posted: Sat May 05, 2018 1:29 pm
by Brett Wilkie

I don't know what happened to all the pictures in the post but here are more.
I am assuming that you have it wired correctly and that you battery is installed as negative ground?
With the ignition off the only wire that remains hot is the thick one that is connected to the battery. If the battery is discharging with the ignition off it suggests that there is a defective diode in the alternator so you may want to remove it and get it tested. also it is very important that you have a good ground connection between your alternator and engine block. Let us know what happens although I might not have internet access as I will be touring for the next six weeks. Here is a bigger picture.

Posted: Sat May 05, 2018 1:45 pm
by 1970 cortina GT
Thanks Brett, enjoy your trip. I have joined the two thick wires that went to the regulator and one of them is permanently live so I’ll have to take them apart and see what I’ve got. Everything else is as you’ve shown. I’ll post results. Thanks again.

Posted: Sat May 05, 2018 2:23 pm
by Brett Wilkie
I assume that you have joined the two smaller gauge wires that go to pins, L and IGN? keep them separate or your charge light won't work and they should only be switched live with ignition ON. If one is always live it will drain the battery just as if you had left the ignition switch on. The two heavy cables are BATTERY+ and the other is to ground the alternator body to the block although yours might not need the ground wire if the alternator is mounted solid in metal brackets?? If you had joined those two together there would be a dead short with smoke and flame.

Posted: Sat May 05, 2018 3:56 pm
by 1970 cortina GT
Ok so following the details way above for converting from generator to alternator with built in regulator I joined the two smaller wires together and put to ignition light on new alternator terminal 1. I joined the two thicker wires together and attached to terminal 2 on new alternator, this is the one that is permanently live and as I trace it back I see that it’s hooked to the same terminal as the power from the battery on the starter. So now I know why it’s permanently live I have to figure out what to change. Ignition light works correctly.

Posted: Sun May 06, 2018 8:51 am
by 1970 cortina GT
Here’s what I’m going by, bearing in mind I’ve converted to negative earth.Image