Please note this thread has been inactive for 90 days. For the best results, please start a new thread.
Results 1 to 1 of 1
  1. #1
    Join Date
    Jul 2010
    Hensley, Arkansas

    Default 1977 Mercury 500 Thunderbolt 50HP engine harness and wiring harness rebuild

    My wiring harness is shot. While trying to test for a shot in the key switch insulation was falling apart as well as the wires just breaking. I cut everything loose from the key switch which tested fine but looks like it is 30 years old (which it is) so I will replace it with a new push to choke key switch. I started cutting back the wiring harness to find good wire but I dont think there is any. Just wire skeletons/remains. The harness is $230 ( I previously rebuilt the engine side wiring harness and at that time considered just building it all from scratch getting rid of the engine and the wiring harness. Any gotchas to doing that? Looks straight forward. Just home runs for each wire to the switch as follows per the attached diagram.

    Red Solenoid to key position A
    Black Solenoid to key position D
    Orange Switch box to key position E
    Yellow Solenoid to key position B
    White switched power from key position F used by the choke and other keyed accessories
    Gray Choke Solenoid to whatever that is on the new push to choke key switch
    Brown unused as I dont have a tachometer


    Attached Images Attached Images

Similar Threads

  1. rebuild wiring harness Mercury 850
    By edyson in forum Mercury & Mariner Outboards
    Replies: 5
    Last Post: December 25th, 2010, 02:59 PM
  2. wiring delco EST to orgional thunderbolt 4 wiring harness
    By 4.3 3rd time a charm in forum Mercruiser I/O & Inboard Engines & Outdrives
    Replies: 4
    Last Post: June 23rd, 2009, 10:46 PM
  3. internal wiring harness on 1977 evinrude 35
    By bama7x57 in forum Johnson & Evinrude Outboards
    Replies: 2
    Last Post: February 12th, 2007, 05:15 AM
  4. 1977 mercury 115 hp external wiring harness problem
    By kyle thomas in forum Mercury & Mariner Outboards
    Replies: 5
    Last Post: May 2nd, 2005, 06:54 PM
  5. Re-wiring Center Console - ignition harness - tilt harness
    By Kesh in forum Boat Topics and Questions (not engine topics)
    Replies: 2
    Last Post: May 22nd, 2004, 02:41 PM

Tags for this Thread

  1. iboats Forum Directory - Over 100,000 forum posts organized by topic