Originally Posted by Tiktaalik

I think the AL69X or the AL129X should fit with the OM617a minor modifications but my question is: will they provide sufficient voltage output for my battery? Anything less than 14.4 will eventually kill my brand new battery.

Does anyone know the idle and above idle voltage outputs of these two alternators? Are there other Bosch alternators out there that fits the OM617a engine and provides a higher voltage output?

Originally Posted by Diseasel300

The '86/87 300SDL's came with the 70A alternator with blade-connector. You should be able to use the alternator from a W124 or W126, you'll have to swap the pulley and spacer since the M103 and OM602/3 use serpentine belts. Not sure on clocking either. The 80A on my 350SD is the stud style and made it ultra easy to convert to a 143A from a W140.

My own opinion: if you're going through the trouble to upgrade the alternator, don't waste your time on a puny one. The original 80A unit on the 350SD was woeful at night. If you had the headlights on, sitting at a traffic light with the brakes on, A/C running with the aux fans blowing, you were sitting at 12.5V - that was all it would do even with a new regulator. Off idle, it would come right back up. If you really want scary, on a cold-start with the afterglow still running and the A/C on, you were at <12V, literally discharging the battery. I realize the W123 doesn't have afterglow and the A/C is less powerful, but why bother going from "inadequate" to "possibly mediocre".

Originally Posted by 81Wagon

Basically, you're going to have to completely replace the wiring from the alternator to the battery (or rather, the little junction box near the battery). Lots of auto parts stores will carry something like an alternator wiring kit (basically just a couple very heavy-gauge (8 gauge should do it) wires and appropriate connectors).

The stock Bosch alternator has a three-prong connector and your car has a plastic plug with three wires that connect to it. The two big wires are positive (+) output from the alternator, and connect to the little black junction box between the battery and the coolant resivoir. The little wire, which should be blue, eventually connects to the battery light on the dash, performing whatever magic is necessary to make sure the light doesn't light up when it should (leaving you unexpectedly stranded with a dead battery and crapped out voltage regulator ). The stock connector will not work with your new alternator, but that isn't much of a problem since you'll have to rewire the alternator anyway.

Once your old alternator is out, you can cut the blue wire about an inch back from the plastic connector end. Attach another few feet of the same gauge wire to it (blue wire if you want to keep with the color scheme). You will need this wire later to connect to your new alternator.

Leave the other wires alone, and protect the stock plastic connector from shorting out by wrapping it with lots of electrical tape (or something, be creative ). Then use a tie-strap to secure it to something. You will always be ready to go back to a stock alternator if need be!

Install the new alternator (it will be a tight fit and the belts will be hard to get back on). As described earlier in this thread, you can take out the four screws in the alternator body and rotate the back half to a point where the alternator's electrical connections and voltage regulator aren't blocked by your car's AC hoses.

Once the new alternator is in, get out the alternator wiring "kit" described earlier. Crimp and/or solder ring connectors onto one end of each of the wires, and attach one each to the two larger junctions in the junction box near the battery (flip the top of the little black box open, there should be two big screws and one little one holding down the wires. Unscrew the two big screws, add in your new wires, screw them back in, and close the top of the box).

Now, route the cables down toward the alternator using the best (shortest) path you can find, securing the wires with tie-straps every foot or so. You also want to route the blue wire from earlier over to the alternator.

The alternator has three connectors: two big, obvious ones (one is just a bolt and the other is a slightly smaller bolt with a flat connector on it too) and one sort of on the opposite side that is a smaller flat connector (recessed in the body of the alternator, not sticking out). Cut the blue wire to the necessary length and attach an appropriately-sized female connector to it, and plug it into the smaller, recessed connector.

The two heavy-gauge power wires each get cut to length and connected to one of the remaining two larger connections using appropriate connectors (ring connectors or a ring and a flat connector).


So in a nutshell, what you want to do is this:
* Connect your old blue wire to the new alternator at the small, recessed connector, and get the old power wires safely out of the way.
* Connect two new heavy-gauge (8 gauge should do it) from the car's power junction box to the power connectors on the new alternator.


You're done! Enjoy your new alternator!





Watts divided by voltage equals amps. So 1500w/13v = 115A, and 1000w/13v = 77A. Using the same equation (and unrealistically assuming everything is running perfectly) you can find that 65A alternator can put out about 845 watts maximum. But I don't think the alternator can put out the max amps at idle speed...