HZJ 78 series 4wd engagement issues.

There is nothing electrical needed to engage 4wd on that model. Sorry Glenn.

" I suspect that the light stopped working after the local garage installed a new clutch for me"

Most likely that is what happened. There is a switch that sticks out of the transfer housing and tells the dash light that 4wd has been engaged. That switch has been smashed and the wires have nothing to connect to. It is hard to access so most people just forget it existed as it doesn't affect engaging 4wd.
The activation itself is purely mechanical.

As for 4wd not working, you need to get it checked out. Most likely cause is a freewheeling hub has been reinstalled incorrectly and is not working. Jack up a front wheel and test that the hubs engage.

Thanks Phil and Glen,
I guess it was just wishful thinking, when I saw that wire disconnected, that there was something electrical in the engagement of 4WD, and easy to fix.
The round switch on the side of the housing isn't damaged, but the wires coming out of it go up 4 or 5 inches to a round plug that isn't plugged into anything. So I guess that's why the light doesn't come on, but that's just a coincidence. I do wonder what has become of whatever it used to plug into......
But thanks for directing my mind to the bleedin' obvious.......:-) I now see that when the lever is put in 4wd (hubs disengaged) the front drive shaft doesn't turn. Therefore 4wd IS engaging. I also find that with the lever in 2wd, and the hubs engaged, the front shaft turns freely- showing that the free-hubs are not engaging.
Come to think of it, the same mechanic who replaced the clutch and seems to have disconnected the 4wd indicator light, also replaced the front wheel bearings. I think that the only time in recent history (I've had the car 5 or 6 years) when the front has been messed with.
Anyway, now I need to investigate why the freehubs are not engaging the front driveshafts......... The dial rotates through its full movement and seems smooth enough. I'll start dismantling and see what I find.
Thanks for your help so far.
Cheers,
Martin

Well after a Sunday spent under Troopy, I can now report that Phil was pretty close to being on the money. :-)
The RHS freewheel hub was full of all the rust and crud under the sun and was not allowing the sliding collar to slide along to engage with the spline. Because I don't have locking diffs, both front hubs need to be driving in order for them to make any contribution to getting some traction.
I'm not 100% sure that mine was previously put together correctly (one of the springs seemed not to be quite right) and I got a lot of help from various YouTube information clips on the subject. Some of them were a bit light on in spots, but overall they helped and with them the rebuild job wasn't too difficult, if fiddly and a bit filthy. This YouTube video was really good and gave a complete and accurate description of the job: https://www.youtube.com/watch?v=-mygIDZlne4
I still don't have a 4wd indicator light on the dash, and if anyone can tell me where to find whatever my wires from the 4wd engagement shaft housing are supposed to plug in to, I'd appreciate it.
Another thing of interest is all the clanking and clicking from the front end that happens when steering tightly when in 4wd. Is that normal ? I've read of the wheels getting "wound up" when using 4wd on tar, which makes sense. But since I don't have locking diffs I wouldn't have expected it to be an issue.
Anyway, It's good to have 4WD drive again, and hopefully I won't get stuck (again !) next time I go bush !
Thanks again for the help,
Cheers,
Martin

far from uncommon for " normal mechanics" to get things wrong on 4wds.

Incorrect assembly of free wheeling hubs is common .... I've had such an expeience.

The correct tensioning of front wheel bearings is another ....... many normal passenger cars can be adjusted by hand ..... 4wds the bearings are large and should be preloaded with the prescribed procedure using a torque wrench and a large socket .......

there are other matters of detail that should be understood.

ya realy need to take 4wds to some one who understands them.

Cheers