View attachment 25954
So I'm left with the front speaker connections & the 2 power sources & the ground on the wiring & try & find a mounting point for the brace!
Red with white tracer is your radio feed (12V+ IGN ON) and black feeds your turn-signal flasher off the same circuit. The orange wires are radio (dash) illumination. If you follow the orange wires, one eventually goes back to the headlamp switch and the other goes to an orange "triple tap" that feeds your instrument-cluster lamp bar.
In other words, you're best off not cutting that connector off the harness. You'll just introduce potential turn-signal and dash illumination gremlins.
See if you can get generic wiring connectors (1/4" flat male, I think) that will push into that connector to power your radio. Tape the existing damage, unless you really feel like pulling the plastic insulator off and heat-shrinking each pair of wires (which is what I'd do, but if we learned anything from the '69 Valiant, I'm really picky about wiring). Wire the illumination or dimmer (green) wire on the new radio into the orange wires. Alternately, you could cut the connector off your OE radio to wire into the new one, then it's a plug-in like OE. Red to red, orange to green.
Looking at the diagram on the back of the radio, it doesn't appear to require a constant (battery) 12V+, which is odd. If you do need a constant 12V+, look for a red "triple tap" female bullet connector. There should be one coming off the wiring for the lighter--not far from the radio--that may have one position occupied for the glove-box lamp (if you have one). Those bullets are an odd size; parts-store or stereo-shop males are usually a loose fit. Tinning them with solder is often enough to make them fit tightly.
Realistically, the ground wire can go to any good chassis ground including the cluster housing. Myself, I much prefer to find an actual battery ground wire in the harness to prevent ground loops, which can create noise in the radio. However, ground wires are few and far between in the dash of these cars.
There is a ground strap that runs from the engine to the firewall; the other side of its bolt on the firewall is the best solution. The ground strap's often (usually?) missing but
it was there originally. If you don't have it, make or buy one. It prevents any number of interior/dash electrical gremlins. Check the HELP! section of the local parts store for Dorman #60213. It's a very nice braided strap. You can also make one from some 10- or 12-gauge wiring and a couple of crimp-on eye rings. The Valiant's strap runs from a bolt I installed on the back of the cylinder head, but I can't remember offhand which bolt on the firewall was used. The OE one was still present and stayed on the firewall throughout the engine swap, so I never had to mess with it other than verifying its continuity.
Other than that, your best bet is likely just to wire it to a screw somewhere behind the dash that goes into the dash structure or other metal. Since you can't easily test its continuity to ground right now, this might require a bit of underdash diddling once everything's in the car with power connected.
Whichever option you choose, make sure there's a good ground between the firewall and engine. A bolt in the back of a cylinder head is best. Barring that, the coil-mount bolt is a convenient location on a small block while B/RB engines can use one of the bolts in the rear intake-gasket hold-down bar. Make sure the underside of the bolt head is clean. Take note of this bit,
@b-body-bob , since you've got engines flyin' all over the place at the moment but none currently in their car. Grounding is absolutely critical on these cars.
