diode problem

I just realized the diodes in my parking light control line from my alarm are over heating. 

They are 3 amp diodes and I am drawing 4.5 amps through them.

I replaced the diodes with 6 amp ones and they are still overheating.

I thought I had it, what am I missing?

I have the photo sensor set so that the headlight/parking lights are always on.

If I remove the diodes the line doesnt get hot at all. just the diodes are overheating.

I believe the diodes are there so if I turn on the factory parking light switch, the voltage doesn't feed back into the alarm.

The diodes heat when the parking lights are drawing only through the alarm.

If I also turn the factory parking light switch on the diodes cool down. I assume, because they can now draw through the factory circut.

All this lead me to believe that its the forward voltage of 4.5 amps through a 3 amp diode thats causing the overheating.  Not any inverse voltage.  So why doesn't a 6 amp diode solve my problem?

I removed the diodes altogether and spliced the parking light alarm/output back together.

I am now using that output as the positive input to the coil of a relay. I did place a 6 amp diode there just incase.

I now have a relay right at the headlight switch. The headlight output from the alarm activates the coil of the realay (also grounded right at the switch.

I now have all of about 4 inches of wire from the relay spliced into the headlight feed and the parking light output. Again right at the switch.

Now the connection out or the relay to the parking lights gets hot.

It seems to be just the point of connection that gets hot.  relay pin to an aluminum female connector, soldered to copper stranded wire. 

All my 2 legths of 4 " splices are of the same guage wire as their donor.

Whats goig on? why is the connection the origin of the heat?  In both situations the heat/breakdown was at a transition. Can there be that much resitance through these differen t materialse? could I be doing something else wrong and  it just shows up here at the weakest link?  Any thoughts?