Charging Conversions #3
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Converting an Externally Regulated to an Internally Regulated Alternator

This is the third conversion I'm detailing and it is for those who have an externally regulated alternator 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 1970 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 it...you get the idea. Work smart and stay safe so you can finish your conversion and enjoy it for years to come.

The pictures below are for the original externally regulated alternator wiring on my 1970 Buick, the factory internally regulated alternator wiring on a 1974 Buick, and a merged diagram showing the proposed wiring for putting an internally regulated alternator in my 1970 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.


1970 Buick Externally Regulated Alternator Wiring
(Diagram is scanned from a 1970 Buick service manual)


1974 Buick Internally Regulated Alternator Wiring
(Diagram is scanned from a 1974 Buick service manual)


1970 Buick with Merged Internally Regulated Alternator Wiring
(Merger of previous two diagrams by the author)

If you've looked over my generator conversion articles, you'll notice that this one is considerably easier - most of the car's wiring remains intact, and we just end up removing a bunch of wires and re-routing the ones that remain a bit.  The indicator light on the dashboard and a bunch of other related things are already in place - we don't need to touch anything under the dash or inside the car. The bulk of the original wiring between the regulator and alternator is gone - all that remains is the main power lead and the wire from the indicator light. The rest of the wiring on the diagram is completely taken from the existing vehicle. (On the generator conversions you end up splicing in wiring from the newer vehicle inside the car. Yuck!) This simplicity explains why this conversion has kits offered to help you complete it - it's a common thing to want to do and it's easy. You can really take the cheap way out and not remove any of the old wires - just hook them together at the proper places and you're done. For a much cleaner conversion, and for better charging performance you should do it right and remove all of the unused wires and route the remaining ones properly. If you opt to not use a kit, you can get the plastic plug with small pigtails of wire attached for the #1 and #2 terminals on the alternator and use that as your basis for the conversion.

You will likely have to disconnect the entire engine wiring harness and partially pull it out of the engine compartment to work on it - you will have to unwrap/untape it and re-cover it (with new electrical tape or the original "split loom" covering if that's what it had originally) before re-installing it. This isn't as hard as it sounds. There will be relatively few connections to manage - one will be at the trans, maybe a few temp and oil pressure switches on the engine, perhaps a brake warning light, maybe a smog-equipment connection near the carb, the coil, and the connector at the firewall. The harness will also go down the front of the engine and to the starter - but don't muck with that end of it. Start from the firewall and remove the connector there by taking out the bolt in the middle of it and gentle pulling the plastic connector towards the front of the car. Proceed down the harness disconnecting one connector at a time until it's all free except where it goes down the front of the engine. Untape the harness so you can do the work you need to and when you're done, tape it back up again - starting from the firewall end. Reconnect all of the connectors to everything it in reverse order you took them off - start out by the alternator and work your way back to the firewall. As you do this, be careful not to mangle any of the little plastic clips that hold the harness to the engine and to the firewall - they're important so the harness doesn't flop all over the place and cause problems down the road.

If you look closely, you will see that the wiring diagram from the existing vehicle has the indicator light going to the regulator, while the merged wiring has it going to the alternator. Since these two components are usually on different sides of the engine compartment, we need to get that wire over to the alternator during the conversion process. The easiest way to do this is to trace this wire to the large factory wiring connector on the driver's side of the firewall, remove it from there, put a nice, new, long wire onto there, and re-install it into the connector. (See my article on Reusing Plastic Wiring Plugs for more details on doing this.) Run this new wire in the harness all the way out to the alternator - there should be plenty of room once you remove the now un-needed wires from the existing harness that connect to the old regulator. Do the same "remove and replace the wire" process to connect your new long indicator light wire to the #1 terminal on the new plastic plug at the alternator.

The main power lead from the alternator will already be in the right place and should be large enough to carry the load you'll be putting on it - I believe 10 gauge is enough for up to about a 100 amps alternator. Just hook it up and slip the little rubber boot back over it. If you've lost that little "boot", or it just needs replacement, go visit your local parts store and get one. That connection has a lot of power going through it, and you don't want it to get wet/dirty (it could short out) or touched by tools or your hand while you're working in there.

There is one other trick in the new diagram - the #2 terminal on the alternator has a black and red wire that connects back to the main output wire from the alternator in the middle of the wiring harness. This is the remote voltage sensing wire for the alternator. Earlier versions of this page suggested attaching this lead directly to the main output terminal on the alternator, but that was written before I understood the importance and function of this wire and I now do not suggest connecting this wire to the alternator output. It should be connected to the place in the wiring harness that is the "main junction point" for the wiring where alternator power connects to the rest of the vehicle and goes off to charge the battery. This can be in the middle of the harness or in a new, dedicated junction block that you add in and mount in an appropriate place. Factory style conversions would do the splice in the middle of the wiring harness, but I prefer the dedicate junction block approach with the junction block mounted on the driver's side of the firewall near the main wiring connection at the back of the fuse block. Note that doing this requires moving some other wires around to make them all connect to the same place, but it's pretty easy to understand if you stare at it for a while.

Here's a quick reminder of what wires are for what purpose on the small two-place connector that goes into a GM internally regulated alternator. The red wire (on the left) is for the remote voltage sensing feature. The white wire (on the right) is for the field connection. The plastic plus has a small "key" on one side to prevent it from being plugged in backwards, so it only fits one way. The terminals inside the connector are standard 1/4" Packard 56 style terminals and you can remove them and replace them with custom wiring very easily. See my Reusing Plastic Wiring Plugs page for more details.

GMInternallyRegulatedAlternatorPlug01.jpg (1503312 bytes) GMInternallyRegulatedAlternatorPlug02.jpg (2029667 bytes) GMInternallyRegulatedAlternatorPlug03.jpg (1856849 bytes)

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.

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