Hello Peter
I can send you a copy of two pages from the IPC which relates to your last paragraph.
It shows that the kit can be installed on the S/N range my TB20 belongs to.
I need an email adress because I can’t upload here a document in a PDF format.
This is the debate linked to earlier, whether a mod which was originally certified by the type certificate holder (Socata in this case) can be simply retrofitted i.e. with just a logbook entry.
We had two avionics guys in that debate. One of them said basically Yes and the other said basically No 
My information from the USA is definitely Yes. Some obvious caveats is that you need to be able to duplicate the factory installation. How this is achieved, the opinion varies. The “European way” is that the installer has no brain and needs to be given clear and detailed instructions, preferably via an STC. The “American way” is that the installer is authorised to work it out
I would start by checking with Socata which airframe S/N range this kit can be installed on. The reply might be hard (impossible) to get but you never know your luck… I was not able (within my time limitations) to find this stuff in the MM/IPC (the CD), but maybe somebody else knows where to look.
Hello Peter,
I have today received the MM CD you kindly sent me.
In the meantime I’ve learned through Troyes Aviation, that Socata has all of the parts available, not as a kit but in separate pieces including the wiring manual. I’ve got the price for the main PCB and I’m waiting for the rest of the components. The only thing which nobody seems to know or care of is whether or not a STC is needed. I still investigate.
Thanks again for the help
Edouard
I’m well aware of the lack of involvement and guaranties from either Troyes or Socata. I have just indicated them the P/N of the PCB for the range of S/Ns, which includes mine, found in the IPC. I will get a quotation next Tuesday (Passover is in the middle) and tell you. I will probably buy from you spare relays just in case…
In the meantime, happy Passover to you and all the contributors to this forum.
Edouard
Remember that Troyes Aviation (and probably any other Socata parts distributor) will not make any checks regarding suitability of the part you are ordering. Even if you tell them this is for S/N 499, no check will be made. I had discussions with them myself (I buy from them too) and they absolutely resist getting involved in that, and it is really hard to get Socata itself to communicate nowadays.
So you need to make sure you are buying the right parts.
I have indeed posted the Q on socata.org and get the P/Ns for the whole kit as well as for the PCB only. Have sent today an email to Troyes Aviation asking them for availability and price quotation. I’ll keep you informed as soon as I get the answer.
Thank you again
Edouard
I see you posted the same Q on the Socata owner group. The man there replied that the PCB is in stock at Socata. I don’t suppose they sell many of them…
It does sound like early TBs didn’t have this master switch (relay board) arrangement, hence Socata made that kit available, many years ago it seems (1980s?).
The only issue is that while stock may exist, it’s likely to be very very old stuff and possibly corroded, internally if not externally – despite being sold with an EASA-1 form I once bought a starter motor from Socata which was roughly 10-15 years old and lasted only weeks because all the lubrication had dried out. A lot of low-turnover parts are very old and this is a general issue in aviation. I have had “new” parts from 1968.
What exactly is your shop not happy with, ECN?
If they want to replicate the later TB “three avionics bus” wiring, they have a fair bit of work to do, beyond installing the relay board.
The S/N is 499
Edouard
