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  1. #1
    Join Date
    Mar 2017
    Location
    Alton, Hampshire
    Posts
    52

    Electrical problem - Please help

    I am very mechanically minded and do all the work on my cars myself, however, I am by no means electrically minded and electrics have always been the bane of my life. Over the past month I have removed the old dash from my Magnum Cobra, built a new dash with new layout and a couple of replacement gauges.

    During the process of removing the old dash I labeled all the wires as they came off the gauges with the plan of simply reconnecting them as they were before. This evening I completed putting the gauges into the new dash and reconnected the wires as they were removed. Once all connected I turned the key - fuel pump started, ignition light came on, amp meter worked. I then thought I'd test everything in stages - turned on the side lights, no problem but once I turned on the headlights all electrical power stopped. No fuel pump running, no ignition light, no nothing!

    I have checked all the fuses, nothing. Could someone please suggest where I should start the investigation.

    Thanks in advance from an electrical numpty!
    Jon LR

    Magnum with Ford 289ci & 4 speed Toploader

  2. #2
    Join Date
    Aug 2004
    Location
    Christchurch, NZ
    Age
    58
    Posts
    2,215
    Check that there is not an earth left disconnected somewhere.
    Cheers

    Myles D-W

  3. #3
    Join Date
    Mar 2017
    Location
    Alton, Hampshire
    Posts
    52
    Thanks Myles. I did check all the earth connections, they look fine. Not sure if that would make sense though. Everything was fine until I turned on headlights, since then there is NO power.
    Jon LR

    Magnum with Ford 289ci & 4 speed Toploader

  4. #4
    Join Date
    May 2016
    Location
    Cheshire
    Age
    49
    Posts
    204
    Any chance the battery is dead, the lights being the final straw?
    Kittihawk: Pilgrim Sumo MK3 built '93/'94 with 2.1L Stage 2 Pinto and Ford Type 9 5-Speed Gearbox

  5. #5
    Join Date
    Mar 2017
    Location
    Alton, Hampshire
    Posts
    52
    No, I'm pretty sure not. It's on trickle charge and never gives a problem. It is definitely as if something has blown / shorted and now nothing is getting power.

    Very strange!!!???
    Jon LR

    Magnum with Ford 289ci & 4 speed Toploader

  6. #6
    Join Date
    Aug 2004
    Location
    Christchurch, NZ
    Age
    58
    Posts
    2,215
    Is there a master fusible link somewhere?
    Cheers

    Myles D-W

  7. #7
    Join Date
    May 2011
    Location
    Flimwell
    Posts
    698
    Assuming all your fuses are ok no power at all sounds like a wire has come adrift somewhere. A bad connection could work at low current but break down completely when a higher current is applied. You really need some kind of tester. If you haven’t got one- make one. A 12v light bulb on the end of a pair of wires. Connect one wire to a good earth (a clothes peg will do) and then touch the other wire to the positive terminal on your battery. The light will come on if your battery is ok. Then simply work your way along the wiring to look for a current. Brown wires are usually unfused live so you should find current on any brown wire. Switched live are usually green so you should get s currrnt on a green wire when the ignition is on.
    The ignition barrel is a good place to start looking.
    HTH.

  8. #8
    Join Date
    Mar 2017
    Location
    Alton, Hampshire
    Posts
    52
    Thank you very much 1dayiwill, I'll do exactly that.

    Many thanks!
    Jon LR

    Magnum with Ford 289ci & 4 speed Toploader

  9. #9
    Join Date
    Mar 2009
    Location
    liverpool
    Age
    45
    Posts
    284
    You can buy the crocodile clips that push onto the ends of the leads for £1 on eBay.

  10. #10
    Join Date
    Jan 2009
    Location
    Dronten, the Netherlands
    Posts
    337
    If you find 12v on the battery terminals themselves, first thing is to make sure there is no corrosion between them and the clamps by cross measuring. So from - terminal to + clamp and vice versa. Then check mass connection on chassis and work your way up on positive side to fuse box and so on. Any relais maybe in feed circuit?

    BR, Theo

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