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Thread: 1974 MGB- New main wiring harness, but no start

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    Jedi Warrior wkilleffer's Avatar
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    Angry 1974 MGB- New main wiring harness, but no start

    Good evening,

    I finally got my dash back in place, harness hooked up, new battery, and was really looking forward to starting the car tonight.

    Sadly, no joy...

    The headlamps, tail lamps, turn signals, and hazard flashers all work. When I turn the key, the ignition light turns on and the fuel pump does its thing. But no cranking.

    I've also noticed no courtesy lamp illumination.

    I swapped the harnesses by leaving a portion of the end of each wire in place so I could color match and plug in the appropriate wire. To the best of my knowledge, I did this correctly.

    Down at the starter, I'm getting 12+ volts, which isn't surprising considering that the lights work. Also not surprising that the appropriate terminals on the fuse box also get 12+ volts.

    Seems like 1974 was a year where the driver's seat belt was required to be fastened before the car would start. Mine would start without it being fastened. Is it possible that in replacing the whole main harness that I inadvertently re-activated that feature?

    Where are some other places to check for voltage?

    Any assistance would be appreciated.

    Thank you,
    -William
    William Killeffer
    East Ridge, TN
    1974 MGB

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    Great Pumpkin JPSmit's Avatar
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    Re: 1974 MGB- New main wiring harness, but no start

    Is your engine grounded? That would be my first place too look. I also once had a similar issue where it was as simple as two reversed wres on the solenoid
    John-Peter Smit
    1976 MG Midget
    1969 Vauxhall Viva GT
    1958 Fiat Multipla (Barn art)

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    Jedi Warrior wkilleffer's Avatar
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    Re: 1974 MGB- New main wiring harness, but no start

    How do I check if the engine's grounded?
    William Killeffer
    East Ridge, TN
    1974 MGB

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    Moderator Mickey Richaud's Avatar
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    Re: 1974 MGB- New main wiring harness, but no start

    Quote Originally Posted by wkilleffer View Post
    How do I check if the engine's grounded?
    There should be a braided or battery cable attached to the engine mount or somewhere along the bell housing or engine block, and then attached to the body. Something like this:

    BH_MG_engine mount.jpg
    "There are three kinds of men. One who learns by readin'. The few who learn by observation. The rest of them have to pee on that electric fence for themselves." Will Rogers
    Mickey Richaud '73 MGB, '69 MGB GT/V6 (SOLD! ), Victor TF, '03 Jaguar XK8
    ------------------------------------------------------------

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    Jedi Knight
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    Re: 1974 MGB- New main wiring harness, but no start

    William,
    On a 74 there should be a starter relay on the firewall. Brown wire comes from the fusebox. Check for hot all the time on the brown at the relay. The seat belt interlock is behind the radio console and has a big white plug with lots of wires. If the interlock unit goes bad it will not let "start" power go to the relay. I have had to disconnect and jump the wires here to make 2 of my rubber bumper 74 GTs starters work all the time. They were hit and miss when starting. I can give more details after I get back from a breakfast appointment if needed.
    Bob

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    Jedi Warrior wkilleffer's Avatar
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    Re: 1974 MGB- New main wiring harness, but no start

    The brown wire has 12 volts at the starter relay.

    I remember seeing the seatbelt interlock when I was doing the harness replacement. What I don't remember is whether or not there were any jumped wires or other obvious modifications. I still have the remnants of the original harness and can have a look at it.

    I wanted to test the relay itself, but wasn't sure how without an assistant in the driver's seat. Live by myself, so someone's not always available.

    Thank you,
    -William

    Quote Originally Posted by bob67bgt View Post
    William,
    On a 74 there should be a starter relay on the firewall. Brown wire comes from the fusebox. Check for hot all the time on the brown at the relay. The seat belt interlock is behind the radio console and has a big white plug with lots of wires. If the interlock unit goes bad it will not let "start" power go to the relay. I have had to disconnect and jump the wires here to make 2 of my rubber bumper 74 GTs starters work all the time. They were hit and miss when starting. I can give more details after I get back from a breakfast appointment if needed.
    Bob
    William Killeffer
    East Ridge, TN
    1974 MGB

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    Jedi Warrior wkilleffer's Avatar
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    Re: 1974 MGB- New main wiring harness, but no start

    OK, that's present. I've taken it off and cleaned the area within the last couple of years.

    Quote Originally Posted by Mickey Richaud View Post
    There should be a braided or battery cable attached to the engine mount or somewhere along the bell housing or engine block, and then attached to the body. Something like this:

    BH_MG_engine mount.jpg
    William Killeffer
    East Ridge, TN
    1974 MGB

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    Jedi Knight
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    Re: 1974 MGB- New main wiring harness, but no start

    pm sent about jumping the seat belt interlock.
    Bob

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    Jedi Warrior wkilleffer's Avatar
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    Re: 1974 MGB- New main wiring harness, but no start

    Thanks, Bob! Just what the doctor ordered...

    Thank you to everyone who participated in this thread.

    Quote Originally Posted by bob67bgt View Post
    pm sent about jumping the seat belt interlock.
    Bob
    William Killeffer
    East Ridge, TN
    1974 MGB

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    Moderator drooartz's Avatar
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    Re: 1974 MGB- New main wiring harness, but no start

    So do we have a vroom vroom moment?
    Drew Frink
    '59 RHD Frogeye Sprite - "Penny" sleeping for now
    '66 RHD Morris Minor - "Maggie" awaiting a non-cracked transmission
    '70 RHD MGB - awaiting a donor engine
    '19 Triumph Bonneville T100 - good to have one that runs

  11. #11
    Jedi Warrior wkilleffer's Avatar
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    Re: 1974 MGB- New main wiring harness, but no start

    We have vroom-vroom... There are still a few things I need to finish, but I couldn't resist a quick spin around the block.
    William Killeffer
    East Ridge, TN
    1974 MGB

  12. #12
    Moderator drooartz's Avatar
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    Re: 1974 MGB- New main wiring harness, but no start

    Woohoo!

    So hard to resist that drive once it's running, even if all else is still not well. If nothing else it's a great motivator to keep going through those last projects.
    Drew Frink
    '59 RHD Frogeye Sprite - "Penny" sleeping for now
    '66 RHD Morris Minor - "Maggie" awaiting a non-cracked transmission
    '70 RHD MGB - awaiting a donor engine
    '19 Triumph Bonneville T100 - good to have one that runs

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