Denso to Bosch alternator conversion.

Steve E · Jun 9, 2020

Hi All hoping for some help.
The Denso alternator on my 05 GS has suffered the seizure and case cracking failure. Unable to source a replacement Denzo, I have acquired a Bosch unit from Motorworks and therein lies the problem. The Denso unit has two wires on the plug, one blue and the other blue/green. The Bosch unit has only one wire on a smaller plug. Looking at the wiring diagram in the Haynes manual, it is unclear to me which wire on the harness i connect the single wire from the Bosch unit to. The wire numbers in the manual do not correspond to any of the wire numbers on the Central Electronics Unit. In fact doing a continuity check between the two plug wires and the CEU pins, the pins at the CEU end have no numbers and therefore i am unable to determine which wires are which. Anyone able to help?

Ian J Hartley · Jun 9, 2020

Looking at the wiring diagram, I would guess that the blue wire (D+) is the key as it’s used on both Denso and Bosch alternators and goes to pin 52 of the ZFE control module.

The Green/ blue wire seems to be specific for the Denso and comes from pin 48 of the ZFE.

You could try just connecting the blue wire, and leaving the Green/blue disconnected and see if the alternator charges. That’s what I would do.

Ian J Hartley · Jun 9, 2020

I notice that the green/blue wire has basic designation 15 attached to it, which usually means in basic automotive electrical systems that this wire is switched live, usually from the ignition switch, though in this case probably derived from the ZFE module.

I would expect to see +12v switched on that line, so make sure if you don’t connect it, it’s prevented from grounding.

Ian J Hartley · Jun 9, 2020

This is an extract from the wiring diagrams.

mikeyboy · Jun 9, 2020

There was a tread here a few years ago regarding this conversion,
There is a repair harness available from bmw,to fit the Bosch unit.
Have a search,all will be revealed

Steve E · Jun 10, 2020

Cheers for the info guys. So i will connect the Bosch to to blue wire and insulate the blue/green. I will also try to see if NOG can get the adaptor wire mentioned in the ADV Rider thread.

Ian J Hartley · Jun 10, 2020

Ii think this is what you need.

Available from Motorworks, but a bit pricey.

Santa-2512 · Jun 10, 2020

Ian J Hartley said:
Ii think this is what you need.

Available from Motorworks, but a bit pricey.

Have a look here,

https://www.realoem.com/bmw/enUS/partgrp?id=0307-EUR-04-2006-K25-BMW-R_1200_GS_04_0307,0317_&mg=61

and match the part.

then visit your local bmw car dealership for a quote, often much much cheaper

The much asked for Nav lead is 50% cheaper than a well known retailer when sourced from the dealership

Steve E · Jun 10, 2020

Just ordered from BMW, Bosch to Denso repair harness Pt No 83 30 0 402 338. This is just a plug and play for £26.20. The wire from Motorworks requires the Denso plug to be cut off, and is more pennies.

Steve E · Jun 14, 2020

Final question chaps. The Denso unit has an over voltage protection wire. Do I need to fit this to the Bosch unit. If so where/how, as there is no bolt hole on the Bosch unit.

Steve E · Jul 1, 2020

Ok Final update. I fitted the bosch alternator and after consulting the electrical dept where i work the consensus was to fit the over voltage wire. Bike all back together and its running like a dream. The charging voltage is 14.3-14.5 Volts so a big improvement over the original alternator.
The Alternator belt that motrworks recommends is too short, you need to fit the original spec. All in a fairly simple job but time consuming.

waggy · Apr 7, 2021

Steve E said:
Just ordered from BMW, Bosch to Denso repair harness Pt No 83 30 0 402 338. This is just a plug and play for £26.20. The wire from Motorworks requires the Denso plug to be cut off, and is more pennies.

I know this post is a bit old but I am going through the same fix as my Denso alternator has cracked. This plug, does it have the Denso socket one end and the Bosch plug the other as this number (and images) just refers to an repair plug with the Bosch plug and 2 wires. It will be a lot easier if it is a complete loom adapter!!

Steve E · Jan 9, 2022

Bit late seeing this , the repair harness only has the dense plug and two wires.

waggy said:
I know this post is a bit old but I am going through the same fix as my Denso alternator has cracked. This plug, does it have the Denso socket one end and the Bosch plug the other as this number (and images) just refers to an repair plug with the Bosch plug and 2 wires. It will be a lot easier if it is a complete loom adapter!!

Steptoe · Jan 18, 2022

mikeyboy said:
There was a tread here a few years ago regarding this conversion,
There is a repair harness available from bmw,to fit the Bosch unit.
Have a search,all will be revealed

I'm a bit late, only just seen this thread..

Here's a couple of pictures of the harness that i posted a few years ago when doing a conversion..

will · Jul 11, 2022

Which wires colours did you use in the end probably going to be doing this myself :thumby:

Is the Bosch unit just one wire on plug :beerjug:

Pale Rider · Jul 11, 2022

Ok just done the Bosch alternator conversion on my 2012 gsa. First thing the wiring is different in that it has the Denso plug directly joined to the wiring loom, no short double ended plug as in Steptoes post above. I ordered the £31 conversion lead from Motorworks but noticed they had only charged me a fiver for it so I thought I’d wait and see what they had sent me, turned out they had snipped a Bosch plug off of an RT loom, even better!! After some initial confusion regarding which wires go were i snipped the Denso plug from my loom and soldered the white wire from the RT plug to the blue wire on my loom, as the Bosch alternator only has one terminal I tapped up my green loom wire and the blue and white wire on the new plug, fired it up and runs perfectly.

will · Jul 11, 2022

Pale Rider said:
Ok just done the Bosch alternator conversion on my 2012 gsa. First thing the wiring is different in that it has the Denso plug directly joined to the wiring loom, no short double ended plug as in Steptoes post above. I ordered the £31 conversion lead from Motorworks but noticed they had only charged me a fiver for it so I thought I’d wait and see what they had sent me, turned out they had snipped a Bosch plug off of an RT loom, even better!! After some initial confusion regarding which wires go were i snipped the Denso plug from my loom and soldered the white wire from the RT plug to the blue wire on my loom, as the Bosch alternator only has one terminal I tapped up my green loom wire and the blue and white wire on the new plug, fired it up and runs perfectly.

Thanks Pale rider that’s exactly info I wanted :beerjug:

will · Jul 15, 2022

Quick update Bosch alternator fitted and working , my wiring was same colours as my denso unit so just fitted new plug , pulley was same size so easy installation thanks for all advice and help :thumby:

Steptoe · Feb 15, 2023

I’ve done yet another seized 1200 alternator job today, still not finished yet. It’s given me serious thought about retiring …. Two of the three bolts holding the alternator in place snapped off. If you’ve replaced a 1200 alternator or know where the bolts are you’ll appreciate why I’m fed up

. To add even more grief the tank (an ADV model is completely full, the bike decided to give up on the petrol station forecourt after filling up. It’s done 117k miles……. Have another bike with the same problem to start work on as soon as this one is finished.

Denso to Bosch alternator conversion.

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