Bob Horner Posted November 13, 2014 Report Share Posted November 13, 2014 Ok one for the electrical gurus......... To set the scene (apologies for length of this)..... I have a tr4 converted to negative earth with a lightweight Revington 40amp alternator fitted. I have a battery cut off switch wired into the ignition circuit. I also have the revington auxiliary wiring loom which gets its power from the battery side of the cut off switch and is switched via the ignition and a relay) Amongst other bits and bobs (interior lights, windscreen washers, radio,map light all low amp stuff) , that loom powers an electric revotec fan which is wired via a relay (there is also an override switch for this wired using a switching relay). I have also fitted relays for the dip and main beams and there are spot lamps and fog lamps. These are wired via relays to come on when the relay is powered by the dip (fog) or main beam (spot) with override switches on the dash which effectively make an earth to latch the relay when in the on position. The power for the lights etc comes from wires connected to the starter solenoid via a further auxiliary fuse box. The issue is that the ammeter shows a positive charge when the lights are on and more positive charge when the fog or spots are on (say 15 to 20 amps). Is thus a result of the source of the lights' power (ie the starter solenoid) or something else? Checked alternator with multimeter- runs about 12.8 volts tick over and gets up to 14 and a bit when revved so doesnt seem to be over charging. The needle on the ammeter rises with engine revs- it seems to be measuring load rather than battery charging. Alternator is three terminal type- big post for current and one to ignition and one to warning light. Light behaving normally -ie on when ignition turned on but off when running. Charged up battery fully to check wasn't in need of amps and still did same thing. No problem starting Any thoughts? Bob Quote Link to post Share on other sites
RobH Posted November 13, 2014 Report Share Posted November 13, 2014 Sounds as though all the loads are connected to the battery side of the ammeter rather than to the alternator side as they should be. The auxilliary loom should be connected there - not to the cut-off switch. Quote Link to post Share on other sites
Lebro Posted November 14, 2014 Report Share Posted November 14, 2014 The ammeter should be connected between the battery, & EVERYTHING ELSE Except The starter motor, & (arguably) the horns. Bob. Quote Link to post Share on other sites
John390 Posted November 14, 2014 Report Share Posted November 14, 2014 A silly question, but did you change the wires round on the ammeter when you changed from positive earth? Cheers John Quote Link to post Share on other sites
snowric Posted November 14, 2014 Report Share Posted November 14, 2014 Bob, You ammeter makes sense, as does the needle movement given the setup you describe. I had this 'problem' with my fan connected from the solenoid and could not understand why, when it turned on, my ammeter suddenly showed the battery charging. It wasn't this at all. If you look at the wiring diagram, if you power auxiliary items like a fan and spots from the solenoid then, when you turn them on, with the alternator running the alternator at 14.4V (vs only 12.xV from the battery) drives current to them and has to do so via the alternator via the ammeter then down to the solenoid. I moved my connections to the alternator side of the ammeter using a TR6 type 4 plug connector to get the right reading on the ammeter with one wire to the ignition, one to the fuel pump, one to the alternator and one to the auxiliary loom (I have since moved it). Now I have an ammeter that reads 'right'. At the same time I have had to uprate the charging circuit between the ammeter and this junction box to avoid suddenly running 70 amps on wires rated at only 50 amps continuous. As long as you don't run beyond your ammeter rating then putting 15 amps across it while you are running the lights/spots should not be an issue. You don't need to use the TR6 adapter. You can use a 'bus bar' - see some at Auto Electric Supplies in the UK. Others here might suggest you put a voltmeter in and avoid worrying about the ammeter at all. I hope this is helpful.. Snowy Quote Link to post Share on other sites
Bob Horner Posted November 14, 2014 Author Report Share Posted November 14, 2014 Thanks for the swift responses - particularly Snowy's helpful hints on how to rectify the issue. Regards Bob Quote Link to post Share on other sites
tthomson Posted November 14, 2014 Report Share Posted November 14, 2014 Hi Bob, If you decide to go the voltmeter route, for a negative earth vehicle, you connect the negative end of the voltmeter to a suitable ground point on the car, and the positive side to the ignition switch (White wire). This will show the voltage when the ignition is switched on. For positive earth vehicles, the voltmeter is connected the other way (+ to ground, - to ignition switch) TT Quote Link to post Share on other sites
TR Mitch Posted November 17, 2014 Report Share Posted November 17, 2014 For positive earth vehicles, the voltmeter is connected the other way (+ to ground, - to ignition switch) The Smiths voltmeter I fitted didn't have any polarity markings and worked when connected either way round (ie it never tried to read backwards). Puzzled at first but then realised it worked with a heater and bimetallic strip rather than any modern polarity sensitive gubbins. If you don't see a + or - marking on your voltmeter then it's likely it doesn't matter. Quote Link to post Share on other sites
rwillfly Posted October 15, 2023 Report Share Posted October 15, 2023 interesting thread going here.... my tr3A ammeter shows +20 with ignition switch on, lights on and engine not running. While driving, lights on, the ammeter shows the same +20. Positive ground, new generator, solenoid, wiring harness(Moss), regulator(from Moss, adjusted) and electric fan. We used the wiring diagram from the Complete and Official Triumph 1953-1961 Service Manual. Pretty straight forward other than some of the harness had to be 'flipped' to accommodate my left hand drive vehicle........which made the diagram view point a bit hard to figure as to whether it is looking at the harness side or the guage side. Any hints regarding 'point of view' would be great. Lights, fan, horn, blinkers, brake and dash lights are working properly. A couple of more months of descent driving weather left in the season I appreciate any trouble shooting suggestions you may have Rick Please wait while image is uploading... Quote Link to post Share on other sites
RobH Posted October 15, 2023 Report Share Posted October 15, 2023 (edited) 10 hours ago, rwillfly said: my tr3A ammeter shows +20 with ignition switch on, lights on and engine not running. While driving, lights on, the ammeter shows the same +20. That isn't right. Firstly the ammeter sounds to be wired the wrong way round. With the engine off, any current drain should show as a discharge. It sounds like the ammeter wiring is totally wrong. I think it may be like this ( with the addition of the ammeter being wired backwards so it shows charge ): when it should be like this. The cure should be as simple as just re-arranging the connctions at the rear of the ammeter. : (Note. There are simple sketches to show what is happening - they are not circuit diagrams for any particular car. The dynamo connection here is shown direct for clarity, rather than via the control box as it actually is. Full screed here: https://www.tr-register.co.uk/forums/index.php?/topic/84514-ammeter-wiring-and-operation/) Edited October 16, 2023 by RobH Quote Link to post Share on other sites
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