I changed battery's but I hooked it up backwards

As Steve said . The fuse protects against installing battery cables backwards or backward hooked jumper cables .

Hello Glen, Bad bad things can happen when you hook up a car battery backwards. If your car has a high quality electrical system it might only blow out one or two main fuses. If not, it can cause havoc on the wiring system and burn out the alternator, computer, sensors, modules, and stereo system to name a few.

hook a test lit at the alt big wire this wire must be hot all times and most of the times is protected with a fusible link prone to burn when hooked backward

well buddy if you hook a battery up backwards then just basiclly cooked your cars computer you gonna have to go get anothrer one

when a battery is installed backwards for any amount of time it blows fuses mainly the large ones in the under hood fuse box

IT SHOULDN'T AFFECT YOU POWER STEERING BUT CHECK THE FUSE FOR THE RADIO

I think the relay switches are under the hood near the winshield, Also there possibly is some fuses in the glovebox as well.

Either the battery got hooked up backwards and there is a blown fuse or a burned fusible link, or you did not connect all the wires to the positive battery terminal (there should be three).

I'm sure that if it got hooked up backwards, you will know about it (there would have been lots of sparking going on).

If this is the case, check fuse #24 in the Power Distribution Center (20 Amp) in the engine compartment. If this fuse is good, it should have power on BOTH sides of the fuse when it is checked with a test lamp. If there is no power on either side, then the fusible link either did not get connected to the battery or is got fried. The fusible link itself is ORANGE and is a 20-Gauge fusible link.

I bet you saw some dramatic sparks when you hooked the jumpers up backwards!
The good news is that if your ignition switch was turned to the "off" position when this happened, the fix may be simpler and cheaper than you think. This car has one or more "fusible links" in its primary wiring. They may look like a thick piece of wire, but they act as super-fuses in the the case of large-scale power shorts and the like. Fusible links are typically in-line, so you won't see them in either your under-hood or under-dash fuse boxes. If you're lucky, you blew a fusible link right off the bat, saving the rest of your electrical system from serious harm.
If your ignition was turned to the "on" position when the battery was hooked up backwards, you have a more serious risk that you damaged your on-board computer. However, even if your computer were fried, your dome light, your hazard blinkers, and probably your headlights and turn signals (different circuit than the hazard lights, believe it or not, even though it's to the same bulbs) would continue to operate.
I'm going to recommend that you should check for one or more blown fusible links. Good luck!

No, there is no main breaker or relay.
If the battery is side post, you may have pinched the rubber between the cable and the battery terminal.
Also check to make sure you didn't hook it up backward.
If that's not it, respond, and I'll try to help more.