Classic/Antique Car Repair: 66 impala not starting, electric fuel pump, 66 impala

Question
My 66 impala wont start. I notice that my interior lights are real dim almost out then they get bright again. When I try to start it I can hear the fuel pump running sometines real slow when I turn the key and sometimes when I turn the key it sounds normal. when I turn the key sometimes I get a click from the starter and most of the time I hear nothing. It seems that my battery has enough power but it varies. I ca't get any more than a click from my starter. I have a good battery, I changed the starter, checked the battery terminals and the negative wire from the battery to the motor and to the front where it bolts to the body and it seems ok. I checked the positive battery wire and it looks ok. It does appear that my horn relay is rusted and my horn sounds sick when I press it. Could all my problems be the horn relay or is there another relay that could have gone bad. MY next step is to replace the horn relay but I wanted to ask the question before I spend the money for a new one. Any help is much appreciated.

Answer
OK, I know Model A's, but your problem should be easy to solve.  First, establish that you do have a good battery.  Get a low cost batt. checker and make sure each cell is good.  A battery should last only 5 or 6 yrs, so if yours is much older than that, get a new one.
Assuming it is good:  Check each terminal for tightness.  You can be fooled here very easily.  The bolts may be good and tight, but the crimp on the cable itself could be loose.  Get the battery fully charged and hold the terminals and see if they get hot when you try to start it.. If there is a problem in this area, the problem connection will get very hot quickly.  Don't get burned.  If they all stay cool, the connections are OK.  Do this same thing for any other connections that are on the way to the starter.  The click you get is from the starter solenoid.  It will click if the voltage is low or if the solenoid is bad.  I did not think the '66 chevy had an electric fuel pump, but if you hear it, it must be there.  The pump draws very little current, so it should sound good unless the batt is very low.  I don't think the horn relay has anything to do with the prob.  Charge up the batt., then disconnect one of the terminals.  Touch the post with the terminal and watch for a spark.  Have everything turned off.  If you get any knid of spark, you have a short somewhere.  There should be no spark.  This would drain your battery.
My guess is that you have a bad battery or a loose connection in the starter circuit.
good luck
jack