Tom has it right although if you can get it to work *properly* with your brake pedal, it will make your brakes last up to 10 times longer because it is capable of doing 80%+ of all your braking needs.
I would definitely put a switch on the gas pedal to disable it as Tom said. If you forget to turn the manual switch off after going down a grade, it'll eat all your horsepower in a flash. I'd go one step further and put in a manual switch to totally disable it. Driving in ice and snow I don't think I'd want it working as it's 1-2-3-4 resolution doesn't have enough finesse to safely drive in those conditions.
To figure out what you have, follow the wires. The Telma unit itself should have a big fat wire from it's frame to ground. This needs to be intact as it can carry as much as 180 amps depending on your Telma model.
Then there are 4 heavy wires going from the Telma to a toaster-sized relay box. There should be another big fat wire coming directly from the battery to that box, providing it with 12 volts. Inside that box are four relays... sometimes the contacts go bad although it'd be rare for all 4 to fail. All you have to do is manually push them one by one and if it's not too bright where you're working, you should be able to see the contacts spark as you manually actuate them. If you get that far, the Telma and relays are all working ok and it's what controls the relays that's not working. There aren't many fuses in the system (mine has none at all)
but there may be one somewhere.
That box may be the end of it if you have a simple system, or you may have one that connects into your ABS braking system if you have one... then there'd be another box that does the ABS and control interface.
If you have one of those and it's failed, you could replace/repair it, or just dump it, rewire and go with the 5 position manual switch and the relay box only for a simple system...
Here are two Telma manuals- one is for parts and the other has a "simple system" schematic... maybe this can help out a bit....http://www.heartmagic.com/TelmaPARTS.pdfhttp://www.heartmagic.com/telma.pdf
One thing to know, however you actuate the thing, Telma (and I) recommend that you make SURE to never leave it on when stopped, like at a traffic light or in a traffic jam situation. The thing will work really well but it relies on it's fans spinning to keep it cool. Two things need to be kept cool- the rotors (which won't make any heat if stopped) and the coils, which get really hot if the thing isn't spinning. According to Telma you can burn one up if left in the "on / stopped" mode for very long at all, especially if it'a already hot from coming off a long grade....