The Thunderbird engine is mounted on rubber mounts. As a result, it’s necessary to install a ground wire from the engine to the firewall. This ground wire provides a ground path for attached engine electrical components. Without the proper grounding connection it is possible that some electrical components will not operate at peak efficiency – especially on 1957 models.
This photo shows two types of engine to firewall ground wires. The smaller diameter wire, a reproduction, is the type installed on 1955/56 models.
The battery ground on 1955/56 models was connected directly to the engine allowing the use of a smaller engine to firewall ground wire.
The 1957 model battery to ground cable did not connect to the engine; it was connected to the firewall near the battery. As a result, it was necessary to install a larger engine to firewall ground cable to insure an efficient ground for the engine components. The original 1957 engine to firewall ground wire gauge was 4 AWG, the same size as the 1957 model battery positive and negative cables.
This photo shows markings found on an original 1957 engine to firewall ground wire. Part numbers have not been found on original 57 cables. The manufactures name “Belden” have been found on those cables that have survived in decent condition. Belden Wire Co is still in business today.
The correct size 1957 engine to ground cable is available from some Thunderbird parts dealers.