Plug n play headlight harness upgrade

[1970FuryConv]

It's an aftermarket head unit I bolted under the dash (Continental TR7412UB-OR). Both the instrument cluster and firewall voltage regulators have been replaced with solid state units.
The radio just acts as if it suddenly lost power. If I leave the high beams on the radio comes back on fine. It only loses power when turning on the high beams.
And come to think of it, the little cigarette lighter USB adapter with its built-in voltmeter will also shut off as if it suddenly lost power too, immediately turning back on.
I'm not too sure whether it's the wiring though - I've replaced the 12 gauge wires going between the battery, ammeter studs and alternator output stud with nice big fat fresh 10 gauge wires (with 14 gauge fusible link at battery terminal). Would the factory wiring between the ammeter, fuse box and accessories still be a problem? I feel like they'd hardly ever see too much current so they'd be more likely to last longer.

Like your 1968 Fury.
Does not have to be your wiring, although resistance in the circuit or poor grounds definitely cause problems.
Could be a problem with the floor dimmer switch. Perhaps internal resistance is causing trouble with finding a current path for high beams. Also, connectors at the dimmer switch get corroded from water damage.
A mismatched relay can draw too many amps.
Since resistance in wiring does not change, and your problem goes away once the high beams are activated, I lean more toward grounds, dimmer switch, or relay. Because nothing electrical works right without good ground, I'd use an ohmmeter to check resistance between headlight grounds and battery negative first. Then look at the dimmer switch. If the connector is OK, I'd use ohmmeter to check internal resistance with switch on. Last, if you have a high beam relay, I'd see if it is aftermarket and see if the connectors are OK.

 

[edbods]

Like your 1968 Fury.
Does not have to be your wiring, although resistance in the circuit or poor grounds definitely cause problems.
Could be a problem with the floor dimmer switch. Perhaps internal resistance is causing trouble with finding a current path for high beams. Also, connectors at the dimmer switch get corroded from water damage.
A mismatched relay can draw too many amps.
Since resistance in wiring does not change, and your problem goes away once the high beams are activated, I lean more toward grounds, dimmer switch, or relay. Because nothing electrical works right without good ground, I'd use an ohmmeter to check resistance between headlight grounds and battery negative first. Then look at the dimmer switch. If the connector is OK, I'd use ohmmeter to check internal resistance with switch on. Last, if you have a high beam relay, I'd see if it is aftermarket and see if the connectors are OK.

Cheers, it's actually a 67 year model. It's got relays for both high and low beam circuits, I tapped into the foot switch wiring up behind the dash (at the wire that lights up the high beam indicator bulb) to a momentary switch that activates the relays. That's why I was thinking it might it might not be the dimmer switch as the radio will die when either the foot or momentary switches are used. Mind you, once when I tried the foot switch, the radio actually stayed on. Only once though - after that, it too also killed the radio. The foot switch also has fresh spade terminals when I went to replace the semi-melted connector with a new one too. I'll check resistance at the grounds though.

 

[1970FuryConv]

Cheers, it's actually a 67 year model. It's got relays for both high and low beam circuits, I tapped into the foot switch wiring up behind the dash (at the wire that lights up the high beam indicator bulb) to a momentary switch that activates the relays. That's why I was thinking it might it might not be the dimmer switch as the radio will die when either the foot or momentary switches are used. Mind you, once when I tried the foot switch, the radio actually stayed on. Only once though - after that, it too also killed the radio. The foot switch also has fresh spade terminals when I went to replace the semi-melted connector with a new one too. I'll check resistance at the grounds though.

Cheers! One of the pitfalls of trying to help on the internet is guess about what parts may be involved and what work has been done. Hope you find the problem at the grounds. Chookas!