Not sure but if you get the click by turning the key on with somebody listening carefully. It is probably bad. The way it should work is the relay contacts remain closed other than if the excess voltage the device sees activates the relay to open the contacts to shut the output voltage down.

Speculating here as even after all these years I have never seen even a picture of the internals. For example there may be two relays in there. The price of the replacement is so high there may be some kind of weird design in there.

I did not mention poor solder joints as I have no ideal of your background. If there is an early chip in there. Bridging contacts accidentally with solder is only one possibility.

Perhaps the gentleman that has reffered to my explanation. Rather than being critical of it can give better help. Various posts are helpful on your thread.

I may ask a member to mail me a bad one at some point to examine. As i mentioned some European electronic circuit designs can be really strange.

Why do really old solder joints go bad sometimes? Besides the obvious reasons Solder itself actually ages.

Even a roll of solder you buy has a shelf life. Best before something like seven years. Flux core solders only gauranteed two year by manufactures usually.

I believe the gentleman on site that rebuilds cruise control components. Or another one not on this site states clearly. If you have resoldered the component do not send it in for repair.