Good morning, Mirko;
PentaxBronica does have a good point about being concerned with the flash trigger voltage. On many of the older electronic flash units from the late 1960s and the 1970s, there could be a couple of hundred volts of DC on those termnals. With the old metal contacts in the bodies and lenses of that time period, this was not a real problem, other than some metal erosion over time. With our more modern cameras with built-in electronics, often you can exceed the safe voltage levels of the electronic circuitry. This will be expensive. A real quick and effective cure is to use something like the Wien SafeSync device between the old electronic flash and the new camera. Then, no problem.
And, the modern large handle grip electronic flash units with the Auto light sensing systems also do have an "Off" or "Manual" switch position to turn off the internal light control system, and convert the unit back to a fully manual electronic flash unit. My Vivitar 365 and Sunpak 544 flash systems will do that.