4H system issues

[wildfire213]

Hi all
I've had a poke around but can't find what I'm after so I apologise if the info is somewhere else already.
My father in law has a 70 series lc, year unknown with manual locking hubs, on his farm in Finland which gets all kinds of abuse and conditions. Recently the 4H system had stopped working which in -25C snow and ice isn't ideal. I've guessed at an electric fault as the 4H switch seems to do nothing at all (no dash light) fuse is fine but before I go through the hassle of fault finding, is there any common issues with the 4wd electrical system I should start with?
Thanks in advance.
Ed

 

[Runekebab]

Here are the things that can be broke, Check for leaks at the pipe http://www.japan-parts.eu/toyota/eu...owertrain-chassis/3616_transfer-vacuum-piping
and the membrane, can be broke http://www.japan-parts.eu/toyota/eu...2_diaphragm-cylinder-transfer-vacuum-actuator and it is controlled by vacum http://www.japan-parts.eu/toyota/eu...ertrain-chassis/3616_transfer-vacuum-piping/2
hope this helps

 

[wildfire213]

Nice one, thanks. Would damage to these cause the dash light to fail to come on? I've worked on cars before where the indication light was there to tell you that the button had been pressed with no indication of whether the system was actually working or not.

 

[Runekebab]

I think so