Section : Electrical Equipment

Mk2 Ammeter Wiring Problem????

Posted By : Jake Stephen Worth, 23-Oct-2006, 03:14pm

• Mk2 Ammeter Wiring Problem????

  Posted By : Chris Mills, 23-Oct-2006, 06:26pm

  Hi Jake
  
  You did'nt mention if your Spit was either Positive or Negative earth
  
  Follow the link if it's Negative Earthed
  
  http://www.caigauge.com/ammeterfit.htm
  
  I don't know if it's safe to reverse the wiring for a positive earthed vehicle, perhaps another members able to comment.
  
  Cheers
  
  
  
  

  • Mk2 Ammeter Wiring Problem????

    Posted By : Chris Taylor, 23-Oct-2006, 08:35pm

    Provided that you are not trying to measure the current flowing to the starter motor, (ie it's only the switched supply that passes through the meter) you can simply swap the connections A and B if your car is positive earth. If you DO connect it the wrong way round, the worst it will do is show charge when the battery is actually discharging. Should be pretty clear which is which if you turn some electrical item on with the engine stopped. Do make sure the connections are totally sound and the wire insulation totally sound and up to the current required (approx 25 amps with dynamo, about 35 amps with a "Triumph period" Lucas alternator) as quite a lot of current is flowing through this wiring behind the dash.

    • Mk2 Ammeter Wiring Problem????

      Posted By : Jake Stephen Worth, 24-Oct-2006, 03:43pm

      Hello, thanks for your help regarding the ammeter - yes sorry should of added more info, my Spitfire is negative earth with a dynamo and control box....the Ammeter link was helpful, is the diragram the same for dynamos?? I'll try the technical help at that same link, unless you or anyone else can help. Thanks again - Jake

      • Mk2 Ammeter Wiring Problem????

        Posted By : Chris Taylor, 25-Oct-2006, 08:50am

        The principle of the wiring will be the same for the dynamo as for the alternator. However that does not actually tell you exactly which terminals to connect to.
        I don't have a Spitty wiring diagram to hand, but you should find that one of the control box terminals "feeds" the system, probably heading off towards the ignition switch. If you were to connect the ammeter into this circuit it should do the trick. Alternatively you could connect it into the wiring off the back of the ignition switch.

        • Mk2 Ammeter Wiring Problem????

          Posted By : Dan Owen, 25-Oct-2006, 12:26pm

          Chris,
          I don't think wiring to the ignition switch would work, or if it did it would be pretty unsafe. Are you thinking of a voltmeter rather than an ammeter?
          
          To wire an ammeter to a car with dynamo & control box is actually pretty simple. If you look on your wiring diagram there is a cable from the control box direct to the starter solenoid which provides a link to the battery. You need to replace this cable with a similarly heavy, like 30 amp heavy, cable with properly soldered & insulated joints (the wee rubber boots over the terminals are a good idea), to and from the ammeter. The whole load, charging or discharging, goes through the ammeter exepting of course the heavy starting current which can run into 100+ amps, the ammeter is not designed to indicate this as there isn't really much point.
          
          How it works - say you are using more juice than the dynamo can supply, say when the engine is just ticking over, the extra is drawn from the battery to the electrical circuits via the control box and this will register on the gauge as a discharge. When the engine is up to speed and the dynamo is charging, it should be supplying enough current to run the ignition, lights, wipers etc direct from the control box, the surplus routes via the ammeter and solenoid connection to the battery, registering on the gauge as charging. When the battery is fully charged the regulator in the control box should trip to prevent overcharging, then you will have no reading on the ammeter.
          
          The main problem with an ammeter is the carrying of very heavy, normally unfused, currents up behind the dash. OK if the job is done properly, but we've all seen how badly some people deal with car electrics!
          

          • Mk2 Ammeter Wiring Problem????

            Posted By : Jake Stephen Worth, 26-Oct-2006, 09:25pm

            Excellent! Thanks for everyones help and advice on this subject - I'll get stuck in this weekend! Cheers Jake