Instructions for installing GM alternator on GL1200

Donald (Poorboy)Pigott

Start by removing both fairing lowers, left horn, radiator, fan assembly & air duct on left side.

You will have to cut the brace out that the horn bracket is welded to. Grind the upper end flush with the flat part of the bracket, as there is a reinforcement plate to go there (pic 027). I used a piece of ¼ X 1 ¼ flat stock to make the reinforcement plate. It has to be tapered to fit. Drill 2 holes to match up with the bolts that hold the fairing to the bracket. Install plate and just snug bolts, as you will be taking it back off shortly.

Remove the left engine to frame bolt that is just above the timing belt cover, inboard of the intake manifold. This is where the lower alternator bracket will fasten. I used a piece of 1/8 X 1X1 angle iron for this. It will be about 3 ¼ inches long. Drill a 13/32 hole 7/16 from one end & 5/8 from the bottom then drill a 3/8 hole 2 5/8 from that one, in same side. Install the bracket using the engine to frame bolt. Trial fit the alternator (you will have to trim the alt. some) using a 3/8 X 3 bolt using flat washers to space it out to just clears the intake & so the belt will clear the timing belt cover. You will have to put the left cover back on for this.

With the alternator roughly in place it is time to install the crank pulley. Take the left cover back off and remove the crank bolt. You will need a longer bolt (about 1 inch longer). Put the crank pulley on using the longer bolt and flat washers as spacers, add or subtract washers so the belt is in line with the alternator and clearing the timing cover. You may have to move the alternator in or out a little. When you have the two lined up measure the thickness of the washers and make a spacer to replace them. The hole in the crank pulley I used was too big so I made a bushing and spacer together. Install the crank bolt with Locktight.

Next you will cut the timing covers to fit around the new crank pulley. Just cut it enough to fit around the pulley (go slow, might as well polish them at this time). Put covers back on.

Put the belt on and pull it tight. Pull the alternator up against the reinforcement plate you made earlier. Make the adjustment bracket and tack in place (pic 23), remove and finish weld (pic 032). Paint & reinstall. You will have to trim the front screw bracket that holds the fairing lower.

The bottom of the radiator needs to be moved forward about 5/8 of an inch. I made 2 spacers that screwed onto the original mounting studs (pics 36 & 39). The mounting bracket for the fairing lowers now go behind the radiator. The bottom hose will reach the engine, just loosen both clamps and wiggle it around a bit. The fan mount will have to be altered some. You will have to remove the left lower leg from the fan mount(pic1). Bend both lower leg mounts toward the radiator core(pic3). I ground a little off of the lower fan shroud to get the fan blade as close the radiator core as possible. This is done to lessen the amount the radiator will have to be moved forward. Both fairing lowers will have to be trimmed some around the lower part of the radiator. The left lower will have to be fitted around the alternator. I used a torch to heat the backside and while still hot put it in place and mold it around the alternator (pic 17). Be careful while heating as not to get it too hot and bubble the paint or melt the plastic. A heat gun would be better. There is a heat shield that will have to be trimmed to clear the alternator also.

To wire it is very simple. Run a piece of 8 gauge wire from the output terminal of the alternator to the positive battery post. (you can also run it to the battery side of the starter relay) Run a piece of 14 gauge wire from a switched 12 volt source to the exciter terminal on the alternator. That’s it!!!!!!!

Please address any questions to Donald Pigott at


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