If you have a rack conversion, there are low cost parts available on eBay and Amazon to resurrect the function of the centre Horn Push.
The parts are: –
1) Transmitter and receiver , should be about $10 (USD) – search eBay for ‘Remote Transmitter PCB Input Power Transmitting Signal DC3.7V4.5V6V9V12V 315 433’.
2) Battery holder, should be about £2.50 – search eBay for ‘CR2032 3v Button Coin Cell Battery Holder Case Box’.
3) 2 x CR2032 batteries, these were about £9 from our local supermarket.
4) Voltage regulator (Buck), should be about £4 from eBay or Amazon, search for ‘LM2596’
Let me know if anyone needs more information.
Best regards – Colin