You are using a stock relay, what looks like a two prong connector, and a third that I cannot tell what style connector but it's OEM.

My sanden I got from you only has a single red wire, so what do I do with the brown wire next to the blue? Just forget about it?

What rating is the blade fuse?

I'm probably going to do this mod. I just need to double check that the fan still works...

The Sandsn's usually only have one wire=+12v. Just connect it to the same + wire of the fan. You can use a universal relay, or a stock one, the terminal numbers should be the same. The relay coil is energized by the existing compressor clutch wiring, and the N.O. contacts of the relay connect +12v to the + of the fan and compressor clutch. Both the - wires of the fan and clutch (if two wire) get connected to ground. I used a 15 amp (blue) fuse in the fuse holder......Rich

The 126's had an external strip fuse for powering the blower. There is a kit available that you can buy an retrofit. From what it sounds like #8 powers the blower too? maybe the externalization kit would help the 123 too?

I think that is basically what I have done....Rich

Now for sale: $25 shipped
 

I now have these available for sale:
http://www.peachparts.com/shopforum/diesel-discussion/356684-f-s-accessory-c-compressor-clutch-condenser-fan-run-together.html#post3350203

Just a tip, for those doing this in the future. The later cars used a relay which incorporated a fuse. It's plug compatible with the plain vanilla relays, and eliminates the need for an external fuse. part number is0015429719:

Apologies for digging up an old thread.
Have you had any problems with the additional current draw from the aux fan running more frequently, or any problems with longevity of the fan? Are you running the stock alternator?
I'm upgrading to a Sanden, parallel flow, and an oversized fan - this seems like it might be a good modification. Not sure what the current draw on the new fan is vs the old, that's something I'll look into.

The relay gets is own fused power from the large wire that powers the glow plug relay, and that fuse is only for the clutch coil and the condenser fan.
I was providing a 15 amp fuse, but have noticed that it needs to be a 20 amp. I now provide a 20 amp fuse, and it seems to be working on all but one system. If a 20 amp fuse wants to blow, there is a problem with either the clutch coil or the fan. This is the case with the most recent system I did on a friends car. He will be replacing the fan first, and hopefully that will solve the fuse blowing problem. I have had no reports of any other problems with the relay mod.

I was more concerned about the extra load on the alternator causing charging problems, but thanks for the info! Once I get my rebuild finished, I may either contact you for a kit, or build my own (i'd like to try to house as much of the system as possible inside the relay box to keep the engine bay looking stock-ish)
Edit - Just noticed that your prototype actually seems to mount inside the relay box. My mistake.

This modification adds only the relay coil current load (minuscule). You still have the load from the fan, and clutch coil in the stock system, but through the factory fuses. This mod also removes the load from the already overloaded fuse #8 (W123 chassis).
Edit: As far as making your own relay using stock parts and wiring, go for it! I wish I could make these using stock parts, so they would look like they were there from the factory, but it would not be cost effective for me. It already takes more time to build these than I am being paid for by selling them. I just do it as a service, even though I don't make a profit.

Well, you'll have more average load on the system if you're cycling the fan on whenever the compressor is running, vs only when the receiver/drier temp is high. That means on average your charging system has to work harder, although the peak current draw is the same.

Anyway, I don't mean to argue, just wanted to clarify what I was asking. If you haven't had any problems with it, I'll probably build my own unit as soon as I can find some parts from a donor car.

Thanks again! And it's always great seeing someone post information about modifications they've created!