4wd not working

[The Boo Crew]

Hi all i need help with the 4wd on my '94 2nd gen 3TD auto. Basically it isn't working! The buton on the gearshift works i have tested it. The vac pipes to the front diff are ok. There is vac to the actuator on the diff to take it out of 4wd. The light on the dash is not lighting and the relay for the 4wd is not clicking. It does work if pin 2 is earthed so the problem must lie further back but i am at a loss HELP! (why do they use this ADD system anyway why not use a more conventional method?) can I bypass the ADD system and just use a switch to move the vac from one side of the diff to the other to connect the front drive?

[The Boo Crew]

I can take that as a no then! The lads and lasses on difflock.com recon this is the place to find out!

[BUSHWHACKER]

There's an electric actuator on the back of the transfer case to engage the front driveshaft, these can sometimes fail due to water ingress or just gum up through lack of use.

If it's not that then suspect the 4wd ecu behind the dash in front of the gear lever.

[NiftyNev]

can I bypass the ADD system and just use a switch to move the vac from one side of the diff to the other to connect the front drive?

You could, but then you bypass all the built in safety features and it won't work anyway if your problem is the actuator mentioned above. This has to engage the transfer first then the detection switches on this signal the ADD system.

Nev