RobRennie Posted June 14, 2021 Report Share Posted June 14, 2021 Hi All, I am replacing the dials on the dash as they are more than tatty and do not match the modern Speedo and Rev Counter I am doing away with the Ammeter and replacing with a voltmeter. Now this is like being on Who wants to be a Millionaire.... I am sure I know the answer but thought I would check... Predictably, when I remove the wires I lose all electrical power - so I think all I need to do is a make a patch lead and connect the two wires together.... my assumption being that the resistor for the ammeter is inside the gauge. From reading the forum this is a pretty common modification - so I would appreciate one of you confirming for correcting... Cheers, Rob. Quote Link to post Share on other sites
Richard71 Posted June 14, 2021 Report Share Posted June 14, 2021 Hi Rob, I had this modification built into my replacement harness and it appears all they did was join the wires together. Richard. Quote Link to post Share on other sites
RobRennie Posted June 14, 2021 Author Report Share Posted June 14, 2021 46 minutes ago, Richard71 said: Hi Rob, I had this modification built into my replacement harness and it appears all they did was join the wires together. Richard. Thank you Richard - I'll give it a go! Quote Link to post Share on other sites
RobH Posted June 14, 2021 Report Share Posted June 14, 2021 Yes that is all you need to do. Just make sure the joint is insulated well. Don't use that point to connect to a voltmeter. If you do, the meter will be on all the time instead of only with the ignition. Quote Link to post Share on other sites
RobRennie Posted June 14, 2021 Author Report Share Posted June 14, 2021 5 minutes ago, RobH said: Yes that is all you need to do. Just make sure the joint is insulated well. Don't use that point to connect to a voltmeter. If you do, the meter will be on all the time instead of only with the ignition. Yep - that all worked. Thanks Rob, good tip on the voltmeter I am going to put a 'clean' wire in off the Ignition Switch - according to supplier, the new gauges do not need a voltage regulator supply - so a tidy switched 12V is needed. Quote Link to post Share on other sites
PeterTRR Posted June 14, 2021 Report Share Posted June 14, 2021 Further to the question regarding amp meters if i read your query correct , do you disconnect the two wires at the back off the amp meter and connect them together .2nd question how do you connect the vault meter into the wiring,does that then mean you can put a bigger alternator in the car. Thank you Peter. Quote Link to post Share on other sites
RobH Posted June 14, 2021 Report Share Posted June 14, 2021 (edited) Yes you just disconnect the wires from the ammeter and join them together. The connection needs to be a good one as a lot of current can flow through it, and it needs to be properly insulated as the connection goes straight to the battery and there is no fuse, so a short to earth could be very bad indeed. The replacement voltmeter should be connected to the switched-live so that the meter only reads when the ignition is on - exactly where that is depends on the car model. The other side of the meter goes to earth. There is nothing to stop you fitting a larger alternator with the standard ammeter. An alternator may be capable of supplying (say) 60 amps but it will only do so if the load asks for it. The ammeter reads the current going into and out of the battery and it is the battery which determines how big that current is, not the alternator. You should only see a high current after starting because the battery has been discharged, and at no other time. The charging current shouldn't change appreciably if you fit a larger alternator, though if it does it is a sign that the battery has a very low state of charge. If a large ammeter deflection worries you then don't rev the engine until the battery has recovered a bit. Edited June 14, 2021 by RobH typo Quote Link to post Share on other sites
Mike C Posted June 14, 2021 Report Share Posted June 14, 2021 1 hour ago, RobH said: Yes you just disconnect the wires from the ammeter and join them together. The connection needs to be a good one as a lot of current can flow through it, and it needs to be properly insulated as the connection goes straight to the battery and there is no fuse, so a short to earth could be very bad indeed. The replacement voltmeter should be connected to the switched-live so that the meter only reads when the ignition is on - exactly where that is depends on the car model. The other side of the meter goes to earth. There is nothing to stop you fitting a larger alternator with the standard ammeter. An alternator may be capable of supplying (say) 60 amps but it will only do so if the load asks for it. The ammeter reads the current going into and out of the battery and it is the battery which determines how big that current is, not the alternator. You should only see a high current after starting because the battery has been discharged, and at no other time. The charging current shouldn't change appreciably if you fit a larger alternator, though if it does it is a sign that the battery has a very low state of charge. If a large ammeter deflection worries you then don't rev the engine until the battery has recovered a bit. I fitted a 60A VDO ammeter when I upgraded my alternator. It only goes close to 60A for a few minutes after a cold start. But I'm old school - I like to see what currents going in and out of the battery and it matches the original instrument. Given that the 60A is flowing unnecessarily around the old dashboard wiring, a wiring rationalization and voltmeter would make more sense- voltmeters only became popular when alternator outputs soared 40 to 50 years ago. Quote Link to post Share on other sites
RobRennie Posted June 14, 2021 Author Report Share Posted June 14, 2021 3 hours ago, PeterTRR said: Further to the question regarding amp meters if i read your query correct , do you disconnect the two wires at the back off the amp meter and connect them together .2nd question how do you connect the vault meter into the wiring,does that then mean you can put a bigger alternator in the car. Thank you Peter. Hi Peter, Actually there were three wires that needed connecting together - on my install, there were two with spade connectors at the top of the meter then one of much smaller wire size at the bottom. They all had brown as part of the wire colour. Of course do not add in the two wires for the dial illumination Quote Link to post Share on other sites
stuart Posted June 15, 2021 Report Share Posted June 15, 2021 10 hours ago, RobRennie said: Hi Peter, Actually there were three wires that needed connecting together - on my install, there were two with spade connectors at the top of the meter then one of much smaller wire size at the bottom. They all had brown as part of the wire colour. Of course do not add in the two wires for the dial illumination The third brown would normally be the permanent live supplying the overdrive relay. Stuart. Quote Link to post Share on other sites
PeterTRR Posted June 16, 2021 Report Share Posted June 16, 2021 Thank you for all the information the car is a TR6 late 68 / early 69 ,i tried to fit an 18 amp on and it set fire to the ignition switch and the coil wire on the fuse side i then put the ordinary alternator back on renewed the wire and put a new switch on. Peter. Quote Link to post Share on other sites
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