Fuel pump switch in v8 90

Hi all, have an '85 90 that has had an engine swap (back in '98) for a 3.5 v8. It has a fuel pump switch on the dash. I can hear it running when I turn the key to position 2, but I don't seem to when the engine is running. Does it shut off when cranking or when the alternator is going? Is it just to prime the lines?

Also - it seems to have been wired to the stereo (maybe just the switch illum) as it turns the radio off when switched off...

If you turn it off does the landy die? If so, excellent - another handy theft deterrent..................... My old 110 has electric pump but only switched by ignition.

Nope. It keeps running. The chap I bought it from kept it switched on all the time. I'm wondering if it is just a priming switch that puts it into high speed, and that this is overridden when pressure ups? If so - would it make sense to switch it off when its running?