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Technical Testing new wiring harness

Discussion in 'The Hokey Ass Message Board' started by ol55, Aug 17, 2018.

  1. ol55
    Joined: Oct 1, 2008
    Posts: 440

    from Virginia

    What is the best way to test a new wiring harness install ?
  2. HotRodWorks
    Joined: Dec 6, 2005
    Posts: 250

    Alliance Vendor

    Hook up the main battery terminals to a battery charger instead of the battery. Preferably one with an amp gauge. Test each circuit one at a time.

    Sent from my iPhone using The H.A.M.B. mobile app
  3. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 7,722


    Engine or chassis harness, either way power it up and see what does/doesn't work.
  4. KustomKreeps
    Joined: Jan 7, 2016
    Posts: 323


    Plug in see if it works.
    Use test lamp and see if it lights up.
    Use multi meter test each circuit.
    lothiandon1940 likes this.
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  5. I installed the harness and tested things as I connected them. Turn signals, lights, power to the starter, etc. I went with the battery but left the negative loose in case I saw smoke.
    lothiandon1940 likes this.
  6. Boneyard51
    Joined: Dec 10, 2017
    Posts: 3,403


    Any time I test something electrical, such as a harness, I wire in a temporary fuse at the source (battery input) before testing. That way you don’t let the smoke out of anything.

    INVISIBLEKID, kadillackid and RICH B like this.
  7. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 4,844


    Do any of you put a low-current (1 Amp) fuse in each position and then intentionally short each circuit to make sure they are all protected?
  8. sevenhills1952
    Joined: Mar 14, 2018
    Posts: 862


    I've mentioned it before. It's easy to fabricate a current limited power source.
    At battery +, close as possible clip in a simple 2 prong headlight.
    So the main battery + lead you now connect to headlight for power.
    You DO NOT want to smoke a wire(s). If you must be replaced.
    Think about using a headlight. Now you still have power but it's limited by headlight current itself. If something gets shorted to ground...the headlight turns on.
    You can still test power anywhere with a test light because it draws less current than headlight.
  9. If it's all new, what are you worried about? Hook it up and turn Shit on. The new fuse block is your safety switch. You should always have a fuse link on the main power feed to fuse block.
    The Wizzard
  10. sevenhills1952
    Joined: Mar 14, 2018
    Posts: 862


    True...but here's the problem. What amperage fuse should that be? The main battery to starter line isn't fused. Then main power to fuseblock would have to be dependent on all the circuits, so maybe 100A. Wires will smoke before that blows.
    Alternative would be to wire everything leaving battery positive for last. Then series in a headlight. If light turns on (key & lights off)...there's a short somewhere.
    My thought is having a "safety valve", test light or meter check voltages as you go.
    Short circuit proof.
  11. ol55
    Joined: Oct 1, 2008
    Posts: 440

    from Virginia

    So the headlight is in series and the other side goes to the positive side of the circuits?
  12. rjones35
    Joined: May 12, 2008
    Posts: 865


    Yeah, I installed mine and dbl checked things and then hooked up the battery. Scared the crap out of me because I didn't realize the wipers were on, and I had all kinds of stuff laying on the windshield. It all went flying all over the garage.
  13. mike in tucson
    Joined: Aug 11, 2005
    Posts: 485

    mike in tucson
    from Tucson

    NEVER connect a battery charger to the system without a battery in the circuit. Many battery chargers output AC voltage....not pure DC. A battery in the circuit will filter the AC. WHY? If there are any electronics in the circuit (ignition, turn signal control, engine control, etc), the AC voltage can ruin the part.....electronics do not like reverse polarity.... although most are protected, it is not assured. NEVER use a battery charger in the circuit without a battery in place!!! We have taken calls from several builders who did the battery charger trick and ZOT!, they
    smoked their electronic component. By the way, you cannot "test" your battery charger by using a voltmeter to see if there is AC coming out.....voltmeter is not responsive enough.
  14. sevenhills1952
    Joined: Mar 14, 2018
    Posts: 862


    What this fellow says is true. Battery chargers usually just have a half-wave rectifier circuit, so essentially ac, and it can be (peak) quite a high voltage, not good for things to run on 12 vdc.
  15. sevenhills1952
    Joined: Mar 14, 2018
    Posts: 862


    Yes, so it's very simple. Battery--ground connected as it should be. The + positive goes through the headlight. You want light close to battery as possible. One side to battery +, other to cable which you will eventually connect to battery +.
    If the headlight draws, say, 5 amps then now everything is current limited to 5 amps. You can't burn wires even shorted to ground. Headlight makes an easy visual aid.
    You can use a clip lead set like this from Harbor Freight to connect it.[​IMG]
  16. A lot of wire harness suppliers suggest the battery charger idea. I'm not a fan. I check each individual circuit as I install / hook up with an appropriate size fuse for the circuit in the power supply.

    When I'm done the wiring job I already know that everything has been checked for operation so I'm not overly concerned about letting any smoke escape. It's a good idea though to have the electrical system fused (appropriate main fuse or fuse links) just in case the unthinkable happens sometime later.
  17. Ralphies54
    Joined: Dec 18, 2009
    Posts: 700


    Use a 12 volt 2Amp trickle charger like a motorcycle or lawn tractor charger. Enough power to run windows, blower moters etc, wipers and so on without frying anything.
    54vicky and scrap metal 48 like this.
  18. This is what I do. Mine came with a big Maxi fuse that protects everything.

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