'70 Challenger Horn Problem

[dmc8163]

I have a 1970 Dodge Challenger with horns that do not work. If I apply power to the #24 wire at the bulkhead the horns sound off. But when I get to the relay nothing makes sense. For example, every wiring diagram I have found indicates that the '70 Challenger has a horn relay with three blade connections. My car has a relay with five blade connections and it plugs into the fuse block. I have an NOS horn relay for a '70 Challenger and it also has three blades. I tried to plug in the three blade relay into the fuse block but the terminals don't line up. When I test the horn button it create a negative (ground)charge when activated. I'm pretty much a novice with electrical stuff but I can't understand why my '70 has a 5 blade relay. And I can't figure out how test the relay. Can anyone help me get my horns working? Thanks

[Bullitt-]

The later models use a 5-blade relay, I'm betting someone changed the wiring to out... try looking at a '73 diagram and see if it makes sense.

[dmc8163]

Thanks Bullit-. I have a '73 diagram and you are absolutely correct.  Does this mean someone replaced the '70 harness with the '73 or did it come from the factory this way? I tried a new 5 blade relay and the horns didn't work. I'm in the dark as to what to try next.

[Bullitt-]

I'm not sure you have a 73 harness, I think all 71 & up use the 5-blade.  I doubt if yours came from the factory that way.

If you have a 5-blade relay use the '73 diagram to check that it is good, the relay portion works the same as a 3-wire, (I'm not sure if their terminals are in the same position) the extra spades are for a key alarm so they can be ignored..
Check  that you have power coming into the relay's 12V terminal of the fuse block, check that you have continuity to wire #24 (your reference) from the relay output terminal of the fuse block, and check that when the horn button is depressed that a ground is created to the relay's ground terminal of the fuse block.  When all of those conditions are met your horns should work.   
  I have not had to deal with this personally but have read that any 3-wire 12V automotive relay can be wired into the fuse block using jumpers to make a working system.