This page details the wiring changes I've done to my 1973 Electra. I did similar wiring changes on my 1975 Suburban and that served as a very good learning experience for this work.

Goal

The goal is to update the existing wiring to include all of the upgrades and improvements I know how to do and to improve the overall electrical system performance. The previous set of wiring changes were done before I knew how to change out individual wires at the firewall connector (resulting in a hodge-podge of patched wiring), before I understood the importance of the remote voltage sensing wire on the alternator (resulting in low voltage throughout the system), and before I understood the importance of using the right size connector for the wire (in one place I have a 10 gauge wire crammed into a terminal only designed to hold a maximum 12 gauge wire). I also want to add in extra things like cruise control wiring, rear defogger wiring, fog/driving light wiring, wiring for gauges to be hooked up without disabling the original warning lights, adding new gauges (transmission temp, oil temp, and rear end temp), adding a "low fuel" warning light, adding a starter solenoid relay, and adding a relay and feed wire for an electric fuel pump.

Comparisons to previous wiring work

There are a few important differences I ran into compared to the wiring changes on my 1975 Suburban, mostly around the firewall connector. The first is that the firewall connector on the Electra has fewer wiring slots in it, and in contrast to the Suburban, all of them are already in use. The Suburban had three sub connectors of 20, 10, and 7 wires for a total of 37 possible wires. The Electra has two connectors of 14 wires each for a total of 28 possible wires. On the Suburban only 25 wires were used, leaving 12 free. On the Electra, all 28 wires are already in use. On the Suburban, the wiring for the rear lights and gas tank runs underneath the vehicle, while in the Electra these wires run inside the vehicle. That accounts for the 7 wire sub-connector with 4 wires used not being in the design of the firewall connector on the Electra. Also, the wiring for the heater/AC system is included in the main firewall connector on the Electra, but is separate on the Suburban, for a net increase of 5 wires on the Electra. The Electra has 2 wires for front cornering lights, but the Suburban has two wires for the original amp gauge, so that's a wash. The Electra also has one wire for a "stop" warning light which the Suburban does not have. The Electra also has one wire for an "oil" warning light, while the Suburban uses a mechanical oil pressure gauge.

One idea I have is to see if the Suburban style firewall connector physically fits into the firewall opening on the Electra without any cutting or welding. If it does, I can have an extra 9 wires (13 for automatic climate control cars, which mine is) without any noticeable changes to the firewall and without any extra places for leaks to creep into the passenger compartment. If that won't work as a straight bolt-in, then I would have to install additional bulkhead connectors or perhaps modify the firewall to accept a Suburban style firewall connector, neither of which is an attractive option. I did a quick visual comparison of a spare Suburban-style fuse block and firewall connector I have sitting in the garage with a spare 1969 Riviera fuse block I have in the garage, and they appear to be physically interchangeable. Even better, the later-model Suburban fuse block has the later-style push in ATO fuses, which are much easier to deal with than the older glass fuses. I've created a tech page to hold all of my research on this so far.

One other detail is the the Electra is equipped with the optional automatic climate control system, which has it's own connections through the firewall that are independent of the normal firewall connector. It uses a special grommet installed into a hole in the lower area of the firewall on the passengers side to route it's unique wiring from the passenger compartment to the engine compartment. A total of 8 wires pass through this grommet. It is not 100% clear from the wiring diagrams, but after a quick physical inspection of the wiring on the car it appears that all 4 of the wires used for the blower in the original heater/AC system have been omitted from the main firewall connector - and from the engine harness altogether. If true, this would allow for an extra 4 wires to be installed into the original bulkhead connector without any other changes. It does appear that the normal heater/AC wiring is still present in the dash wiring harness, and thus it would need to be removed from the bulkhead connector if those connections were to be reused.

Specific Changes

These are the new wires and components that need to be installed into the engine compartment harness.

•  Fog Light Relay Feed Wire
•  Driving Light Relay Feed Wire
•  Cruise Control Indicator Light Ground Wire
•  Cruise Control "Engage" Feed Wire
•  Cruise Control "Hold" Feed Wire
•  Transmission Temp Sender Wire
•  Oil Temp Sender Wire
•  Fog Light Relay
•  Driving Light Relay
•  Starter Solenoid Relay
•  Fuel Pump Relays (two required)
•  Horn Relay
•  HEI Power Relay
•  Circuit Breakers for all high amperage relay feeds
•  Larger Headlight Feed and Ground Wires (10 gauge)

These are the new wires and components that need to be installed into the dash harness.

•  Fog Light Switch and Wiring
•  Driving Light Switch and Wiring
•  Cruise Control Switch, Light, and Wiring
•  Transmission Temp Gauge and Wiring
•  Oil Temp Gauge and Wiring
•  Rear Axle Temp Gauge and Wiring
•  Rear Defogger Wiring, Timer, and Switch
•  Warning Light "Control Box"
•  Automatic Headlight Control Wiring (Twilight Sentinel or aftermarket control box)
•  Interior Light Controller and Wiring
•  Retained Accessory Power Controller and Wiring

These are the new wires and components that need to be installed into the body harness.

•  Rear Axle Temp Sender Wire
•  Rear Defogger Wires
•  Fuel Pump Power Wire

These are the new wires that need to be routed through the main firewall connector.

•  Fog Light Relay Feed Wire
•  Driving Light Relay Feed Wire
•  Transmission Temp Sender Wire
•  Oil Temp Sender Wire
•  Cruise Control Indicator Light Ground Wire
•  Cruise Control "Engage" Feed Wire
•  Cruise Control "Hold" Feed Wire

These are the new wires that need to be routed through the firewall separate from the main firewall connector.

•  Fuel Pump Power Wire
•  High Amperage Feed for Future Stereo System Use

Firewall Connectors

The list below tells what each wire color is and what it is used for, in table form. These are for the left hand connectors, the engine compartment side. The wire colors are mostly unique within each connector, but there is some overlap, which is why the location is important.

Upper Connector

Lower Connector

This is the original firewall connector with the wire colors for each slot. The connectors are show as if you were looking at the connector end, not the end with the wires coming out of it. Every connector except for the main power feed is a "Packard 56" style connector. The main power feed wire should be a "Packard 59" style connector - the same one that is used for the headlight connectors.

This is the original firewall connector for automatic climate control equipped cars, which mine is. Note that 4 slots in the upper connector are empty in this case. Otherwise, nothing is changed from above, and that is why no separate "wire use" tables are given for this case.

TODO: Create "wire use" tables and color diagrams for the "new" truck style bulkhead connector.

Comments? Kudos? Got some parts you'd like to buy/sell/barter/swap? Nasty comments about my web page so far? You can email Mike or Debbie.

Page last updated 04/26/2008 11:41:08 PM