I have an older rental house with a furnace that is at least 23 years old (the date stamped on the blower motor is 1983). I don't know the make or model... I can find out, but I don't think it will be relevant for my question. Here is my problem. Someone got into the furnace and messed with the wiring... and I need to straighten it up.

There is a black and white power wire coming to the furnace from a fuse panel. There is a 24v transformer, a timer, a relay and the blower motor... pretty simple stuff really. I need to know how all these units get tied together. The thermostat wires go directly to the gas valve, then another pair of small wires go to the 24v sides of the transformer... but everything else is unhooked. The transformer has a black wire and a white wire, the timer has three black wires labeled "Line", "Load", & "Limit". The relay has a black wire, a yellow wire, a red wire and two small gray wires. Then there is a black wire and a white wire going to the blower motor. I'm sure there is a simple concept to this, but I have never worked on this type of furnace, so I want to make sure.

Anyone familiar with this?

Red wire comes from transformer to the thermostat, comes back om white, then passes through at least one safety limit then to the gas valve. Fan limit controls can be hooked up different ways and if you don't know how it was wired previously you can send 120 volts through the entire low voltage circuit, burning out ever thing and I can't tell you from here. It would be nice if there was only one way manufacturers do things, but there are literally thousands of different furnaces out there and all of them are quite different.