I have been messing with this all night, as soon as I put a fuse in it pops with keys out and no brake pedal being pressed, the fuse was blown when I got the car and put one in seemed to fix the problem, went out again today and now every time I put a fuse in it pops. But the brake lights light up when alarm is set...... im so lost only thing changed was I put a radio in it is a 92 hatchback

 

Try removing the radio to test if it still pops

 

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On thing to check is the wiring between the hatch and the body. I have a 96 that kept blowing the fuse for the taillights and it was an exposed wire between the hatch and body.

 

Took radio out and still does it. Anf sorry added info

 

Took out brake switch and it still popped as soon as I put a fuse in

 

Unplug the horns and horn relay.

 

Did you tap into the brake lights wire for radio constant power?

 

Unplugged horn and relay still popped it I habe no idea what it can be

 

After you answer the radio question, this^ test provides an enormous amount of information, if you study the circuit diagram I posted.

 

You seem to be MIA. I'm hoping it's because you figured out the issue. If not these might be helpful for your aftermarket deck and will help you rule out the possibility you cut into the wrong wire (should use an adapter plug made for the 92-95 civic radio plug, but not everyone does). Here is very handy install dr images that I used the first time to get the wires properly and to repair the factory plug to stock that is so often cut away:





After that if you are still blowing the fuse and you don't understand what Ron is getting at. Since you unpluged the horn and the horn relay you have ruled out the majority of those two legs of the circuit thus leaving only the wiring to the tail lights.

Overall this is accurate but there is a leg of wire from the under the hood fuse box from pin #2 of connector C202 (White/Green wire on the 2 pin brown connector on the back of the under hood fuse box) that runs through the firewall to the horn relay connector C434 at pin 2 (White/Green wire that the relay plugs into).

If there is a short to ground in that leg of wire, pulling the relay would not make a difference and you still could pop fuse 42. If that segment of wire checks out as not shorted (pull the horn relay and connector C202 from the back of the fuse box, test between body ground and pin #2 of connector C202 for continuity, no continuity is good for this test) then the short will have to be on the leg of wire running to the tail lights.

Hmmmmm, dumb *** me... The leg to the brake lights and interlock is still connected so the bit I just mentioned won't actually isolate just that leg of wire going to the relay... Without ripping the wire loom open and finding the tie in, there really isn't a way to test just the leg of wire the runs to the relay under the dash. Unfortunately you will have to visually inspect the loom throughout the dash (from the relay) to the firewall, then again on the firewall to the underhood fuse box to see if you see any worn through spots of the loom (wire harness).

Hate when I think I've thought of a snippet easily overlooked only to realize my epiphany was less of an epiphany. *sigh*

Okay so digging a little deeper. C202 from the under hood fuse box actually runs to the left kick panel connector C417. It's at that connector that it splits it into the two legs, one running the the horn relay and horn and the other leg running to the Key interlock switch and the brake switch.

So if you locate C417, unplug it and then unplug C202 and test body ground to pin #2 of C202, you can rule out or isolate the short in that portion of the wire harness. If you don't have continuity then you know it's past C417. Either the little bit from C417 to C434 (horn relay) or the other leg that eventually makes it's way to the tail lights.

I haven't taken a a physical look of C417 but it says it's a 20 cavity white connector. I suspect all the pins are tied together aka a junction instead of pass through connector. Now I'm not sure but I think the male side of the junction is the tie in and won't have wires coming out of it. I think the female is where the wires are but are not connected. If that's the case pulling the female of C417 will let you test each leg separately.

One leg goes pin 7 of connector C427 and pin 1 of connector C423, the other leg goes from C417 to pin 2 of connector C434 and pin 2 of connector C220.

Looking at this, with all the various connectors, it's a bit of work but with pulling pins out of connectors etc, you can isolate exactly which portion of wire the short is in with a multimeter.

The FSM coupled with the ETM is really your friend for all this.

When you took out the brake switch and popped the fuse, was that with the horn disconnected and the horn relay disconnected ?