Snow chains
 

I have a 98 E-350 Ambulance,with snow chains,that have stoped working. Can anyone tell me where to start looking for the problem? I did check all fuses.
Thanks

Is it safe to assume that these are the "On Spot" chain system? If so, check with a test lite if you have voltage at the switch. Depending if you do, or don't ,will determine your next steps. There may be a separate fused supply for the chain system where the fuse has been placed under the dash before the switch.

I do seen to have power to the switch. I can hear a ticking sound when I turn it on.Should I check the air pump next?

That ticking sound could be a faulty relay or a short in the system causing a circuit breaker to constantly be opening and closing.
It would be a good idea to check if the air compressor is getting the voltage to it. If it is and the compressor won't run to build up the air pressure it may need to be replaced. Let us know what you find.
The ticking sound could also be the solenoid that allows air from the compressor to go to the air chamber that moves the arm with the chains next to the wheel.

snow chains
 

There is no power to the air compressor! After the switch I lose it in the harness. (too many wires to trace) I don't know if this has anything todo with it but I don't have power to the cig. lighter either. I have changed all fuses I can find.

There is something you can try.
Run a temporary jumper wire from the battery positive post to the compressor.
Just touch the jumper to the hot feed wire at the compressor and if the compressor runs that would confirm all is OK after the compressor. I would look for a relay between the switch and compressor because that is a pretty heavy load for the switch alone to carry.
If you can't locate the break or the relay I can assist you to install a new relay to get the compressor working if you need the assistance , it's not difficult, all you need is a relay & two fuse holders , one to feed the compressor when the relay is energized and one to protect the system if there is a short from the switch to the relay.
Having worked on ambulances before , the wiring can be a nightmare depending on how it was done.
There should already be a fuse to protect the circuit from the hot supply to the switch and you may not need the second fuse holder.

The compressor works fine with the jumper wire. I don't have a clue as to where the relay is. there is 2 panels full of them. one over head in the cabin the other is in the compratment with the oxygen tank If we find a bad one? where would i get a new one?

Since this is an add on system look for a relay that is different from the usual standard Ford relays. I know it can be a pain to find it , but since it is an add on feature look for a relay that probably is not in the standard relay panel. Once you find it , take it to any automotive supply store and they should be able to provide a replacement. I'm pretty sure it's a standard relay . It may even have a separate mounting on it so it could be mounted away from the usual relays.
Can you trace the color wire back from the compressor , it should lead you to the relay or at least follow that color wire .`

snow chains
 

Ok It will be warm tonarrow I will try to follow the wire back

We're jumping the gun a little here, Since you have a means to check for voltage , once you find the relay you might do this;
1. Make sure you are getting the signal from the switch to energize the relay
2. verify that you have voltage available at one of the relay terminals (may be supplied through a separate fuse) so that when the relay is energized it can complete the path to the compressor
3. Make sure the ground for the relay coil is a good connection or the coil won't operate to close the relay itself.
Usually the relay will have two terminals that are for energizing the relay coil.
Another terminal should have a heavier gauge wire bringing battery voltage to one of the relay contacts. That wire should have a fuse in it for circuit protection.
Another terminal should have a heavy gauge wire that should get energized when the relay contacts close and go to the compressor.
Now you know the path and the procedure checking it out should be a piece of cake.
Have a Happy New Year !

When you find the relay pull it out or turn it over and if it has terminals that are numbered with 85,86, 30 and 87 let me know if you want to and I can tell you which terminals are for what, Thanks