Also, Check that the bulb socket grounds have good connection to the radiator core support, and the support is grounded to the battery.
When I re-wired my headlights (with relays, and new light socket connections), I added an additional ground wire that goes from the battery cable ground wire point to all the headlight ground terminals, in addition to (in parallel with) the normal ground wire that connects to the core support.
On the hot side, to reduce voltage drop (and take the current load off the bulkhead connector), mount the relays near the headlights.
I am using the sealed Bussman relay/fuse block (Eaton 15303-2-2-4). It holds 5, 35-amp mini-relays and 10 fuses. 5 of the fuses are used to fuse the relays. The box is mounted where the battery would have been (rear mounted the battery.) Only 2 of the 5 relays are used for headlights (high and low beam), the other relays are for radiator cooling fans (2), and the last relay can be used for different stuff like horn relay, driving lights, A/C clutch, ect.