VR V8 Cuts out when driving, horn beeps once and kicks in again

[4runner]

Afternoon Ladies and Gents,

I have an issue with my 94' VR V8 Auto Berlina Sedan.

It runs fine and then the motor will cut out and stall, it will crank but will not start again for anywhere between 2 to 40 minutes afterwards.
After a stall a successful ignition will be accompanied by a single beeping of the horn.

Key is in good condition (although the battery might be getting flat.)

Any ideas on hunting this problem down before I send it to the mechanic and have everything replaced that doesn't need to be?

Thanks,

- Andrew