Lee Dutton Posted June 12, 2011 Report Share Posted June 12, 2011 Sorry for all the questions lately but trying to do the stuff myself and it is a learning curve, and as I am finding out, there is a wealth of really good knowledge out there with you guys My tr4a is negative earth with alternator and is fitted with a voltmeter (which doesn't appear to work) 1. how can I test the voltmeter? 2. what should the correct wiring be? is the wiring the same for both guages? 3. If the volt meter is faulty should I replace it with an ammeter or another voltmeter? thanks in anticipation Lee Quote Link to post Share on other sites
Steve Brabazon Posted June 12, 2011 Report Share Posted June 12, 2011 Hi Lee, To test a voltmeter just connect it straight across the battery. It should read around 12V. When wired in a car it is again wired straight across the battery but this time through the ignition switch The wiring to an ammeter is completely different and unless you want to change your wiring you will need to stick to a voltmeter. Steve Click on thumbnail Quote Link to post Share on other sites
Ashley James Posted June 12, 2011 Report Share Posted June 12, 2011 Alternators tend to produce more current than Ammeters can cope with, so the needle keeps going off the dial. I'd stick to a voltmeter. Ash Quote Link to post Share on other sites
ianc Posted June 12, 2011 Report Share Posted June 12, 2011 Lee - the article which Jim Christie and I had in TR Action 248 (March 2011) might help, and I am sure the Office will have a back copy. If not available, send me a PM (Personal Message). Ian Cornish Quote Link to post Share on other sites
Red 6 Posted June 12, 2011 Report Share Posted June 12, 2011 I have just had to deal with this issue on my 4a rebuild. The new autosparks loom with alternator conversion does not have the ammeter wires. When questioned they explained in summary that ammeters and alternators are not good news for reasons mentioned by others. The solution would be to fit a voltmeter in place of the ammeter, or leave the ammeter in place and do not bother about it not working as there is a charging light in the circuit which will tell you if there is a problem, just like with modern cars. To fit a voltmeter is very easy, as has been explained but I would suggest that you check out which wires are actually connected to the Vm as this may shed light on why it is not working. If the Vm is connected to the brown wires where the Am used to be it wont work, but those wires need to be connected to complete the circuit. Take a look at the wiring diagram of a tr5/5 with an alternator and an ammeter then compare it with the later tr6 with a voltmeter and an alternator. You will see how it should be wired. The diagrams are in the Brown book. Hope this helps. ps Voltmeter every time. Quote Link to post Share on other sites
North London Mike Posted June 12, 2011 Report Share Posted June 12, 2011 The solution would be to fit a voltmeter in place of the ammeter, or leave the ammeter in place and do not bother about it not working as there is a charging light in the circuit which will tell you if there is a problem, just like with modern cars. LNK has just that, but I decided to continue fixing it until it was proper broken. So spent a weekend making a stand alone loom, heavy duty, fused coming and going (over kill) double insulated the contact points on the back of the ammeter (cause of 90% of dash board fires), connected it all up, nothing !! Fried the already iffy ammeter............................that was 4 years ago This has just reminded me to get the dial down to Speed Cables and get it re build for higher amp-age, watch this space...................... Quote Link to post Share on other sites
Red 6 Posted June 12, 2011 Report Share Posted June 12, 2011 Excellent, if it aint broke...break it! Quote Link to post Share on other sites
littlejim Posted June 13, 2011 Report Share Posted June 13, 2011 I'm running the original ammeter with an alternator, with everthing running through it. Despite initial trepidation and lots of varying advice on how to wire it in, it works OK so far. Quote Link to post Share on other sites
Ade-TR4 Posted June 13, 2011 Report Share Posted June 13, 2011 It you wire the ammeter output back to the battery side of the soleniod or directly to the battery, the ammeter doesn't recieve the "charge" output. It won't show if the battery is being charged, however, it'll only show discharge. Does save the need to beef-up the wiring behing the dash though. Ade Quote Link to post Share on other sites
ianc Posted June 13, 2011 Report Share Posted June 13, 2011 If the alternator is of modest output, such as the LRA101, originally fitted to the TR7 and peaking at 34 Amps, then the ammeter will scarcely ever see any overload. I have this alternator and see only about 28 amps charge very briefly after starting the car on a winter's day (yes, the car DOES go out in the wet and the winter, as long as the roads are free of salt). However, if you go in for frying oncoming motorists with your auxiliary lamps and have many other electrical extras, you might be pushing your luck! In such cases, the change to a voltmeter is a wise precaution. Remember that the ammeter measures the current flowing into/out of the battery, so as long as your alternator is coping with the electrical load, the ammeter will be reading near zero. However, if you stop the engine and leave all the Blackpool illuminations on, then your ammeter may well suffer terminal damage! Of course, you can be clever and feed spotlamps and other auxiliaries via relays which will be energised solely when the ignition is ON, and this can help avoid such problems. Ian Cornish Quote Link to post Share on other sites
Menno van Rij Posted June 13, 2011 Report Share Posted June 13, 2011 I changed my TR's dynamo for a 1989 Suzuki Swift / Nippon Denso alternator and got rid of all the extra wiring. Having experienced a 'behind the dash' fire with my Spitfire, I opted for the safest solution: Advance Auto Wire's multi fused system and a Voltmeter. Not really needed with a modern day configuration; I even thought of installing a period correct clock instead of the ammmeter. Stuart pointed me towards a period correct voltmeter and that's what I have installed. Never looked back. Have a look at this and look for 'stock schematics' The TR250 and TR6 both have voltmeters. You can see how these are installed. ('73 TR6) Advance Auto Wire Menno Quote Link to post Share on other sites
Ashley James Posted June 13, 2011 Report Share Posted June 13, 2011 Probably the safest way to connect an Alternator is straight onto the battery too and not through old wiring because it probably won't like that many amps. If you do this everything else can stay the same and you'll just have to get used to the ammeter showing a discharge. Ash Quote Link to post Share on other sites
Guest ntc Posted June 13, 2011 Report Share Posted June 13, 2011 (edited) I have just had to deal with this issue on my 4a rebuild. The new autosparks loom with alternator conversion does not have the ammeter wires. When questioned they explained in summary that ammeters and alternators are not good news for reasons mentioned by others. The solution would be to fit a voltmeter in place of the ammeter, or leave the ammeter in place and do not bother about it not working as there is a charging light in the circuit which will tell you if there is a problem, just like with modern cars. To fit a voltmeter is very easy, as has been explained but I would suggest that you check out which wires are actually connected to the Vm as this may shed light on why it is not working. If the Vm is connected to the brown wires where the Am used to be it wont work, but those wires need to be connected to complete the circuit. Take a look at the wiring diagram of a tr5/5 with an alternator and an ammeter then compare it with the later tr6 with a voltmeter and an alternator. You will see how it should be wired. The diagrams are in the Brown book. Hope this helps. ps Voltmeter every time. I beg to differ on this I also had Autosparks make me a loom up everything relayed alas they missed one wire out( cost a lot to sort out and they had no answer) uprated alternator with std amp meter and all works fine Edited June 13, 2011 by ntc Quote Link to post Share on other sites
Red 6 Posted June 14, 2011 Report Share Posted June 14, 2011 Re my loom, I spoke to autosparks about this 3 weeks ago and have an email response from them outlining exactly why the wires to the ammeter have been deleted, why ammeters and alternators can be problematic and their advice to fit a voltmeter if I wanted to see voltage as well as a charging light, thus I have no axe to grind on this issue. I can however add that on my beloved TR6 race car, it used to eat alternators and the problem was traced a faulty ammeter. I changed the ammeter and the problem went away.....for a while. When this occured several years ago I was not as conversant with car electrics as i am now or I would have deleted the ammeter and fitted a voltmeter, for no other reason than it was 1 less thing to worry about, and 1 less thing etc was V important at the time. By the way the loom is a standard loom which has been altered by AS to delete the regulator and add the alternator. For my next project I will try a relayed loom with a decent fusebox as you have done. Of course I will expect to get a circuit diagram with it this time!!! Quote Link to post Share on other sites
MadMarx Posted June 16, 2011 Report Share Posted June 16, 2011 I stay with my ammeter because it can tell you if the battery is getting bad. Things that a voltmeter cant tell you. The disadvantage is that you have strong currents behind the dash board. Cheers Chris Quote Link to post Share on other sites
tthomson Posted June 17, 2011 Report Share Posted June 17, 2011 In an ideal world, you would have both and Ammeter and a Voltmeter so you can check the state of the battery and the load characteristics when charging the battery and running the car, but since the dash space only has room for one of these, you need to decide which is more important for the system you have, or fit the missing one somewhere else. In general Alternators provide a good current output so the voltage is useful. A dynamo has brushes and these wear, so measuring the current is useful. There are no hard and fast rules so fit what best suit your needs. TT Quote Link to post Share on other sites
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