Tail Light Wiring Connectors Are Different

[jimrob]

I have a '64 Monza convertible. The wiring harness for the tail lights is not like the electrical schematic shows. First of all, the connector on the left side is round and has three wires while the connector on the right side is angled and has two wires. The schematic shows the left side wires to be certain colors while the actual wires are different colors. There are no splices anywhere indicating that anything has been changed from the original. The wire assembly that I want to install in the left side came with two wires and the angle shaped connector. How should I wire it to the car?

[terribleted]

The ideal solution is to source a proper left side tail lamp and install it instead of the right side one you have. The tail lamp unit you have has only 2 wires one for the stop/turn function and one for the tail lamp function (the left side tail light unit also has only 2 wires just a different plug). The third wire in your left side receptacle (brown in diagram) feeds to the license lamp and then continues on to the Tail lamp function of the right side light unit. You should be able to connect the tail lamp bulb filament to the double wire (tail lamp) side of the socket in the wiring harness and the brake filament feed to the single (brake/turn) wire of the wiring harness and it will function fine. If you mix up the wires the tail lamp will glow brightly when tail lamps are on (should be dim) and the dim filament will work with the brakes on or the signal selected. If this is what you get simply reverse the 2 connections at the plug into the harness.

[bbodie52]

The answer to your question comes from looking at the purpose of each wire. Each side uses an 1157 bulb, which as two contacts and two filaments. Ground return for both filaments is the bayonet base/lamp socket. Each 1157 bulb only requires TWO WIRES — one for the tail lamp, and the other for the brighter (dual purpose) turn signal/brake filament. The right lamp socket — with its two wires — fulfills the requirements of the 1157 bulb. So why does the left socket have an extra wire?

The answer is that there is only one wire that travels from the instrument panel light switch to turn on the tail lights. When the headlights/running lights are activated by turning on the light switch, power is applied to the rear via the wire labeled 20 BRN. If you trace this wire from the 10 wire multi-connector, it runs to the left bulb socket AND THEN CONTINUES TO THE LICENSE PLATE LIGHT TO POWER IT. From the license plate light socket, another wire (labeled 20 B — 20 BLACK) then continues on to the right tail lamp socket, where the circuit ends. So the left side 3-wire bulb is actually a 2 CIRCUIT bulb, just like the right bulb socket. The only difference is the extra wire from the left bulb that continues the tail lamp circuit to power both the license plate light and the right tail light. The wire color change (from BROWN to BLACK occurs at the license plate lamp socket.

The other rear bulb circuits power both the left and right turn signals. Since these are separate functions, they require separate wire circuits, with color codes 20 DG (left turn/brake lamp) and 20 B/Y (right turn/brake lamp).