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MG MGB Technical - Ammeter; how to connect

Hi, I want to install an Smiths ammeter in my '75 BGT. Does anyone know how I should connect the ammeter?

Gerbrand
Gerbrand

Maybe this will help:

http://members.aol.com/danmas2/ammeters.htm
Dan Masters

Gerbrand - If you will check the archives, there is a thread there regarding ammeters vs voltmeters in the MGB. Basically it says that ammeters are not a real great idea, both because they do not tell you what the condition of the battery is and they require a very large current carrying wire inside the passenger compartment of the car. On the other hand a voltmeter monitors the condition of the battery and requires only a small gauge wire that can be fused to eliminate any damage if a short occurs along the wire. Good luck - Dave
David DuBois

Traditionally, an ammeter is spliced onto the alternator output wire to the battery.

On an MGB it is the thick brown wire that goes from the alternator to the starter.

You can do this without cutting into the harness by using tab and spade terminals where
the thick brown wire connects at the starter soleniod.

DISCONNECT the battery before doing anything!

More caveats:

1) You will be adding length to the amount of distance that the electricity must travel
to the battery in order to keep it charged. That means you'll be adding electrical
resistance. By today's standards, the output of a Lucas 16ACR alternator is rather
weak-kneed and can barely keep up if many items are turned on simultaneously
(lights, heater fan, turn signals, wipers, etc.). Adding an ammeter into the circuit
will only make things worse. Because of this, use a thick, automotive grade wire to
keep the added eletrical resistance to a minimum. The thicker, the better. Say,
#10 or #8 wire, or thicker.

2) You're playing with LIVE, UNFUSED wires here. Any sudden disconnection or accidental
grounding due to poorly made terminals, or chaffed (worn) wire insulation can be most
inconvenient...or disastrous. If something should go wrong later down the road, at minimum,
you'll lose your battery(s). At worse case - you can easily start an electrical fire.

This is no place to be cheap, or for short-cuts.

* Use thick rubber bushings wherever the wires must pass through bulkheads or sheet metal.

* Crimp AND solder the wire connectors and use heat-shrink tubing as stress relievers.

* DO NOT merely twist bare wires and wrap them onto the terminals at the back of the
ammeter. Use the proper crimp on "O" terminals at the back of the ammeter.

* Use thick electrical tape to wrap, cover and protect the exposed terminals at the back of
the ammeter.

In my case, I protected the ammeter wires by sheathing it's entire length inside rubber hose
(fuel line).
Daniel Wong

Daniel, thank you for the helpful advise. I was in doubt wether I should splice the ammeter on the thick cable coming from the alternator, or on one of the thinner cables. I already had planned to change the battery- and startercables for thicker ones with soldered connetcions. I have done this on my previously owned GT6 and the heater fan, wipers and indicators operated faster than ever.

David, I am aware of the fact that an ammeter isn't of very much use. I will explain why I want to have an ammeter installed. My B had a radio installed when I bought it. I never listen to the radio in a classic sportscar, because I like to listen to the engine, so I removed the radio and now I'm filling the hole in the console with a panel where I can place gauges. So why use an ammeter as one of these gauges? I found a never used ammeter on my parents attick and I also found a used vacuummeter. In my opinion its just fun to have some gauges, displaying information that is of no use. In normal driving, we don't really need a revcounter and oilpressure meter as well, but they are there and they give the dash a nice sportscar look.

Gerbrand
gerbrand

An ammeter must be in the heavy gauge wire, since it must be wired in series with the current source. That means that all the current must pass THROUGH the ammeter. That's why David is right about his caution that you are placing wires carrying lots of current into the passenger compartment.

A voltmeter, on the other hand, is placed in parallel with the current source. That means that it can sort of watch the current flow past without really being caught in the larger flow. The bulk of the current flows PAST the voltmeter, not through it. Therefore, only a thin wire need be run from the connection point to the meter.

Given that the ammeter offers little advantage and several potential dangers, I would skip the alternator. I understand about having lots of gauges. The presence of meaningful gauges, rather than idiot lights has always been one of the differences between an enthusiast's car and a grocery carrier.

Its your car, so do what you like. If you are careful and do things right, there is no reason that you can't safely install an ammeter.
Paul Noble

Since ammeters usually display charge and discharge they are connected in series with the battery (starter excepted) to show whether it is being charged or discharged. If it were in series with the alternator it would display the total current consumption of the electrics and only ever show a discharge if the alternator were faulty and draining the battery. Hmmm, maybe that would be more useful than trying to determine at night whether that needle is on the charge side of zero or the discharge ...

Neither an ammeter or a voltmeter will ytell you much more than the warning light, and like the temp gauigae and the oil pressure gauge is just one more variable to worry about. It is said that the oil cooler was only made standard because owners kept taking their cars back in summer compaining about low oil pressure. As John Twist says, "Buy yourself some nice driving gloves instead".
Paul Hunt

Hi..

Modern cars are usually fitted with fuses in the high current feeds (fuse values can be 100A or more) and could be fitted to a 'B', but MUST be fitted correctly.
I guess they really pay for themselves in the event of an accident, when all sorts of shorts could happen, and maybe start a fire.

Sometimes the 'fuse' is simply a length of lighter gauge wire, and is not obviously identifiable.

High current fuses and holders are availible from specialist auto electrical suppliers, or from the breakers for the thriftier amongst us (like me)...
hey, it's recycling really.

Don
Don

Don,

What you're referring to is normally called (at least on this side of the Atlantic) a "fuse-able link". It is usually a short length of wire, designed to melt when the current exceeds its rated value. But then, that's what a normal fuse does.

MGB's did not come from the factory with fuse-able links, but one could be fitted. The drawback to them is that they normally require tools to replace and are often fitted in the wiring harness. This makes side-of-the-road repairs difficult. But then, a fuse-able link should only blow under extreme circumstances, in which the alternative is likely a catastrophic fire.
Paul Noble

This thread was discussed between 21/02/2003 and 24/02/2003

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