Charging Conversions #1
Home Up Next


Converting a Generator to an Externally Regulated Alternator

This is the first conversion I'm detailing and it is for those who have a generator now and want to take their charging system one step forward in life. To demonstrate this process, I'm going to go through the steps I outlined in my Alternator conversions for older GM's article for my 1958 Buick. You should also take the time to read the suggestions outlined in my Reusing Plastic Wiring Plugs article for ways to get a cleaner appearance to your wiring efforts. As always, disconnect the battery while doing this sort of stuff. Take your time, and think about what you are doing. I am not responsible if you do something wrong and fry something - including yourself. This information is provided for informational purposes only. The lawyers made me do get the idea. Work smart and stay safe so you can finish your conversion and enjoy it for years to come. Also, if you own an older Buick with the "push gas to start" feature, check out my page on preserving this feature after you convert from a generator to an alternator and my page on Nailhead Alternator Brackets.

The pictures below are for the original generator wiring on my 1958 Buick, the factory externally regulated alternator wiring on a 1963 Buick, and a merged diagram showing the proposed wiring for putting an externally regulated alternator in my 1958 Buick. I did these graphics by scanning in the pages from the factory manual and messing around with them in paintbrush (the drawing program that comes with Microsoft Windows) until I got what I wanted. Simple enough, huh? Compare them and read on for more details.

1958 Buick Generator Wiring
(Diagram is scanned from a 1958 Buick service manual)

1963 Buick Externally Regulated Alternator Wiring
(Diagram is scanned from a 1963 Buick service manual)

1958 Buick with Merged Externally Regulated Alternator Wiring
(Merged from the previous two diagrams by the author)

You'll notice that I had to add wiring not only for the regulator and alternator, but also for the indicator light on the dashboard and a bunch of other related things. The bulk of the original wiring for the generator is gone - all that remains is the factory ammeter and wiring to the battery itself. The rest of the wiring on the diagram is completely taken from the newer vehicle.

If you look closely, you will see that the wiring diagram from the newer vehicle includes wiring for the ignition switch and related things - since we don't need to replace all of that stuff to do the conversion, we just need to use that piece of the diagram as a reference when splicing into the existing wiring. By looking carefully at the diagram we can see that we need two wires - one that comes off of the ignition switch and gets power when the key is in the "run" position (the yellow wire that goes to the indicator light in the example) and one that gets power in the "accessory" position (the pink wire that goes to the fuse block in the example). We will use these two wires as inputs to the new harness. Looking at it some more, we see that the pink wire goes to the fuse block, through a fuse, and back out as a black wire again. This is important - this wire must be taken from the "fused" (or protected) side of the fuse block when we do our conversion so that bad things don't happen if a short develops. Also, this wire then goes to a special 10 ohm "resistance" wire in the harness - without this special resistance in the circuit things won't work right, so we need to put that into our conversion somehow. I'm told by my readers that a Radio Shack 10 ohm 10 watt 10% wire wound ceramic resistor (part #271-132) has worked well for their GM vehicles. Your mileage may vary, but if your system is similar to the system described here, this should be a good starting point for your work. As with any resistor work, be careful as resistors get very hot in certain cases - especially if they are overloaded - and stuff can melt.

Next, we need to consider the size of the wire that carries the output of the alternator back to the place where it joins up with the large battery cable. Assuming no extra electrical load has been added in the rest of the cars electrical system, the feed wire that takes power to the rest of the car will be adequate, but the alternator to battery wiring path must be able to take the full output of the alternator. Think about the case of starting a car with a run-down battery - for that first minute or so when the engine does start, the alternator is going to be pumping out a lot of power to recharge the battery and run whatever else you have going inside the car. For most cases 10 gauge wire is enough, but if you're going to a high amperage alternator, make sure the wire size is adequate before you install anything. Be smart and be safe.

Lastly, we can see that we will need to improvise some sort of junction block where all of the power for the car (other than the starter motor) comes together. By comparing a few other diagrams with the actual wiring in my car, I know that I have a junction block right next to the existing regulator that the the main battery cables connect to. I also know that this junction block is on the "battery" side of the ammeter - but I need one on the "alternator" side to function as the main junction point for the wiring and a place to hook up the remote voltage sensing wire to. I need the conceptual equivalent of the "bat" terminal on the original regulator. On my 1958 Buick, the "10 red" wire that runs from the junction block to the ignition switch is already correctly wired up to the ammeter wiring under the dash - I don't have to worry about this wire on my conversion as long as I hook up the ammeter properly. To add a junction block is simple - once you have one to add. You can get them from various places - including junkyard scrounging if needed. My favorite is to use one intended for a mid-'70s GM pickup for "accessory" add-ons, though MAD Enterprises makes one as well. They have a insulated center screw and a nice plastic protector around it - and they can be had from most parts stores for a few bucks. When working with an ammeter, the key is to have everything that draws power on the "alternator" side so that it properly shows if your battery is draining or charging. If you end up moving wires around, this is very important. In my case, it's already mostly handled correctly and I have no wires to move around - I just need a place to join the output wire from the alternator to the input wire to the factory ammeter.

At this point, I have all of the basic details hammered out and I can start poking around on the car. As I start laying out the harness on the car, I will see that there are already two wires that run from the regulator to the generator - the field wire and the main output wire. I still need a field wire in the new scheme, and if the main output wire is big enough I can just re-use that, though that's doubtful and it should probably be replaced. The only other wires I need between the regulator and the alternator as the "R" wire (18 LT. BLUE in the diagram), and the ground connection between the two components (14 YELLOW in the diagram). In my case, the original main output wire for the generator is off-white and around 14 gauge. The field wire is already pinkish, and about the right gauge. For my conversion, I will re-use the off-white output wire for the new ground wire (it likely already has the right connections on both ends already) and just add a new 10 gauge red wire and a 18 gauge light blue wire for the new alternator output and "R" terminal wires, respectively. This will prevent me from having to cut up my original harness much if at all for now. I could also file the harness away and build a new one if I wanted to - I may just do that in the end so I know the new wiring is in good shape all around. The area around the regulator will be quite crowded when things are done, but it's doable. I'll need to hook up all of my new (and some of my old) wires to the new regulator and route all of the needed wires to a new junction block. If I do it closely enough, the small pigtail of 16 gauge white wire from the new plug I bought for the regulator will reach the new junction block and save me the trouble of splicing in a longer wire for the remote voltage sensing feature. If I end up needing a longer wire, I can easily remote the wire from the plastic plug and use as long a wire as I need to reach the junction block without splicing.

The remainder of the wiring is needed to hook up the indicator light under the dash and get the proper resistance wire in place. Since both wires join together at the same terminal on the regulator, you can make your life easier and just run one wire out to the regulator - running a wire through the firewall is a pain. Running two wires is twice the pain, so make life easy on your self and run one wire out and make the split into two wires under the dash. The resistor can be wired to get power from any accessory feed - the radio feed is one choice, read your factory manuals for other ideas. (Often the fuse block has extra un-used accessory feeds you can tap into...) The other side of the resistor can be used for your junction point by running two wires to it. One will go out though the firewall to the regulator, the other will go up to the regulator side of the warning light. Mount the indicator light somewhere where you can see it (varies based on your car and if you feel like poking around in your dash too much to install it) and hook the other side of the indicator light up to an ignition feed. Again, hunt the manuals and the fuse block for ideas.

That's about it. If you made all the connections right, nothing should freak out when you reconnect the battery. You should be able to start the engine and immediately have your alternator start powering the system. A good start-up sequence is to check that connecting the battery is OK, then turn on the ignition but don't start the car. The indicator light should go on. If not - stop and fix the problem right now. If your new indicator does light up, then start the engine and make sure the indicator light goes out. You can use the troubleshooting procedures from the "newer" manual to isolate any problems in your newly upgraded charging system.

Comments? Kudos? Got some parts you'd like to buy/sell/barter/swap? Nasty comments about my web page so far? You can email Mike or Debbie.

Pretty much everything on this website is copyrighted, if you want to use something, ask first.

Page last updated 01/01/2010 03:20:57 PM