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MG TD TF 1500 - Ammeter question

I mentioned that my ammeter is stuck between middle and + and doesn't move when i use any lights or electrical devices.
Don't have an electrical diagram in front of me, but knew with some cars the power goes through the gauge to the coil... (or somewhere equally important).
If i am not getting anything going through it what are the odds i won't have any power going to the coil/distributor?

(not a mechanic, or an auto electrician)

Am thinking i will pick up a cheap ammeter and run it in parallel and mount it under the dash until i get the stock one looked at?
g.b.lawson '53TD

Gordon - All the power except for starter power goes through the ammeter, so the only thing wrong with the ammeter is 1) the vane that caries the needle is jammed against the coil or some other obstruction is keeping the needle from centering with no current through it and 2) the previous owner may have bypassed the meter entirely. You can remove the meter to have it repaired/overhauled and just connect the two wires together and insulate themuntil you get the meter back. There is really no need to get another meter while the original is gone unless you are really interested is seeing what is happening with the current. Good luck - Dave
David DuBois

My temp guage was stuck at 85 degrees for some time (won't go into just why...scarry story). Since the car was in storage since 67 I wasn't too surprised. But I was able to correct the problem very scientifically with a moderate rap on the back of the temp guage with the handle of a screw driver. It works perfectly now. Is it worth a try for your ammeter?
Gene Burgess

Having an electrical engineering background, I felt the following comments might be of interest.

One might well ask, why does all the power go through the ammeter? Or, why an ammeter and why not a voltmeter?

Cars of yesteryear showed the driver amperes in the electrical system, whereas, todays cars show voltage in the system.

I'll try not to get too complicated with this.

In actual useage, an ammeter gives much more usefull information as they indicate the LOAD on the system, whereas in a modern car with a voltmeter or God forbid, no voltmeter and an idiot light to indicate abnormal conditions, this only indicates whether your electrical system is being fed the correct power from your alternator.

Actually, an ammeter is really a voltmeter in which a big shunt - big enough to carry the maximum load of your entire car, is put in line as Dave has noted, and the miniscile drop across this shunt is converted to millivolts and read on the "ammeter".

It is true that a modern car with only a voltmeter will show when a load is placed on the system as this causes the voltage to drop. But with an ammeter, one can extrapolate an actual quantiative (directly measurable) indication of the changing load.

Also, it should be noted that an ammeter is more expensive to produce than a voltmeter.


What I can't figure out, is why the works elected to make the water temp gauge read in SI units (old - "metric") whereas the oil press. gauge is in Imperial units.

Does anyboy out there have greater wisdom than the Abingdon works?

Gord Clark
Rockburn, Qu.
Gordon A. Clark

Gord - If it is any consolation to you, the MGAs and MGBs went to Imperial units for the temp gauge.

Gene - The definition of a real technician is one who knows the exact spot to kick the equipment to make it work ;).
Cheers - Dave
David DuBois

"If we change this to "XX UNITS" the gauge should "read" just about center under normal operation. (as opposed to "off the scale") "That way we can use this gauge instead of haveing one made for us"
Considering the $$ whoes or our friends in Abingdon whilst they were building our cars I wonder if this was a consideration?
David 55 TF1500 #7427
David Sheward

There is no question that you have to take the ammeter out and see how it works. Since it is also a voltmeter, nothing prevents you from applying for a second the voltage of a small 1.5 V battery, it should go full scale.

Denis L. Baggi

Not sure why it is "stuck" half way to the + side... not crazy about disassembling it...but not going to spring for a new one right now... will remove it later in the summer.... for now i will run an aftermarket one in parellel.
g.b.lawson '53TD

Disassembling it is no big deal, I have done it many times. If the needle is stuck, it is easy to make if move freely. Otherwise, the coil could be repaired easily, it is a few turns of a thick wire soldered on the terminals. There are those like John Marks at Vintage Restoration who make a great looking item out of a wreck, though.

Denis L. Baggi

This thread was discussed between 21/07/2004 and 01/08/2004

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