280SE 4.5 90A Alternator wiring question - PeachParts Mercedes-Benz Forum

andrewc · #1 08-06-2012, 11:51 PM

purchased a bosch 90amp internally regulated alternator from a audi 4000/vw quantum and am going to attempt to wire it up tomorrow when it arrives. my question is this. to those of you who have upgraded to a higher output alternator, what did you do with the 3 wires going into the factory plug that plugs into the side of the alternator, and the 1 heavier gauge wire with the boot on it which i assume is for the battery connection. any ideas of how i should wire up the new alternator with these 3 wires as the connection on the new 90amp alternator does not have a 3 prong female connection on it.

andrewc · #2 08-06-2012, 11:56 PM

this is the backside of the new 90amp alternator.

and this is the stock mercedes 3 wire connector going into the alternator i have now.

andrewc · #3 08-07-2012, 01:06 AM

took the old alternator out tonight and found the 3 wires going to plug are black, brown and red w/ a blue tracer (stripe). hope that helps.

daddi · #4 08-07-2012, 02:01 AM

Does the original plug have two big and one small connectors? If it does i would think the two big connectors go to the same connection up to the battery and the small wire goes to the light. If so you connect the big wires together under the bigger bolt and the smaller wire single under the smaller bolt.

andrewc · #5 08-07-2012, 02:06 AM

Quote:

Originally Posted by daddi

Does the original plug have two big and one small connectors? If it does i would think the two big connectors go to the same connection up to the battery and the small wire goes to the light. If so you connect the big wires together under the bigger bolt and the smaller wire single under the smaller bolt.

no, the three wires in the plug are all the same size. heres a photo.

andrewc · #6 08-07-2012, 09:29 PM

does anyone know which of the 3 wires pictured goes to the dash light? im thinking if i can figure out which wire goes to the dash indicator and tie that into the 1 new heavier gauge wire from the new internally regulated alternator to the battery, i can essentially just bypass or "get rid of" the old non functioning external regulator and wiring yes? does that sound like it will work? someone has got to have done this before...

andrewc · #7 08-08-2012, 07:44 PM

out of pure frustration of not being able to find the needed answers to my questions from scouring the web, i have scratched the new audi/vw alternator idea and ordered a bosch al72x and a new voltage regulator. i hope this will fix my charging issues. i guess we'll see come monday/tues. when the new parts arrive...

andrewc · #8 08-10-2012, 07:14 PM

figured it out, its charging! out of curiosity i "fiddled" around and got it figured out and working great. i ran a wire from the small bolt on the alternator to the red w/ blue tracer and blue wires that are joined in the plug for the voltage regulator. i made a new wire from the + terminal on the alternator and ran that to the stock junction block on the fender that the original wire bolted to. everything works and no more dim generator light on the cluster. cant tell you how happy i am to have a properly charging electrical system. the h4 autopal headlights i installed tues. are nice and bright. looking forward to going for a cruise tonight to see how proper headlights should look.

hope this info may help others with a w108 that are looking to add some more "juice" to their car.

Palolo · #9 08-10-2012, 07:38 PM

Thanks! It'll help me, that's for sure.

I have a Bosch upgrade Alt waiting to pop in (AL72X) to my 108 2.8SE and was wondering the exact same thing. Plug mismatch stalled the project, but now I think I can proceed. I wonder what the difference between AL72X and the VW one you have is?

I have been waiting to put in the new Alt, then I will look at converting from mechanical rad fan to electric, and an electric water pump plumbed in to the lower rad hose (delete thermostat, plug bypass), effectively modernizing the coolant flow control.

Cheers,

Pat

andrewc · #10 08-10-2012, 08:20 PM

Quote:

Originally Posted by Palolo

Thanks! It'll help me, that's for sure.

I have a Bosch upgrade Alt waiting to pop in (AL72X) to my 108 2.8SE and was wondering the exact same thing. Plug mismatch stalled the project, but now I think I can proceed. I wonder what the difference between AL72X and the VW one you have is?

I have been waiting to put in the new Alt, then I will look at converting from mechanical rad fan to electric, and an electric water pump plumbed in to the lower rad hose (delete thermostat, plug bypass), effectively modernizing the coolant flow control.

Cheers,

Pat

Pat, from my week of searching, the Bosch AL72X is a 55amp alternator, and is a direct plug and play install. from what ive read, its externally regulated and has the same 3 prong connection that stock 35amp unit that came on our cars. i dont think youll have to do anything with the wiring. i actually purchased an AL72x and a new voltage regulator two days ago when i decided to ditch the 90amp unit. i guess ill put them up for sale here when they arrive. dont quote me on any of this info about the AL72x being a direct plug and play swap, as i i havnt seen any of the parts in person, but from what i have read from my weeks research, it seems to be a direct swap. youll have to let us know how it goes, and what, if any, mods are required to make the AL72X work in a w108.

Palolo · #11 08-10-2012, 08:40 PM

Yup, it (AL72X) is a 55A alt., but it is an upgrade from my stock 35A alt, apparently (I have a M130 '71 280SE 6 cyl).

Appears to be internally regulated though... At least this particular one.

aggmeister2010 · #12 09-15-2019, 10:20 PM

Hey folks, reviving this one. I have the Audi 4000 alternator arriving tomorrow...I need the extra amperage to support the dual electric fans I'm installing in my W108 to replace the clutch fan.

I see @andrewc made a post on wiring - looks like the thicker wire from the positive post goes straight to the terminal block (direct replacement, with 1 awg wire), and the blue/red and blue wires go to the negative terminal.....what about the third wire from the original harness?