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MG TD TF 1500 - Ammeter causes car to cut off?????

My 52 TD will run and then cut off, I can tap on the ammeter (Lucas) and lights will come back on and I am able to start the engine again. I can tap on the ammeter and it will cut off again. Is this a bad ammeter? If it is any suggestions on how to repair?
J.A. McWhirter

First thing I'd do is to check and see if the nuts are tight on the wire studs. (Disconnect the battery before you reach back there with a wrench.) Bud
Bud Krueger

I have done that. This has been a constant problem since for 12 years. Now it has gotten so bad that the car stays in the garage. Any suggestion on a work around or a suggestion on replacing the ammeter. My car is a weekend driver.
J.A. McWhirter

I'm currently (no pun intended) working on my two ammeters & have just finished reading all of the threads in the archive. Tapping on an instrument isn't generally recommended but I agree with Bud in that it seems to suggest one of the terminal wires is loose, or it's also possible that one of the two solder joint inside the instrument may have a cold joint & a poor connection. Your tapping could dislodge a wire, short & do considerable damage. The issue/symptom you have was described on a couple of the threads in the archive, however as I was looking for images, I didn't note them. Just had a quick scan again but couldn't see it. Search using 'ammeter' in the thread title. There are about 30 threads in total. Bud's 'Refreshing 30 amp ammeter' gives a good overview with plenty of pics. A very simple instrument & easy to work on.

I did see one unanswered question in relation to the screw at the rear. This is generally covered with a varnish as the position is set on the bench at manufacture. It's function is simply to enable the installation of the pivot. We used to use nail polish to secure screws during instrument rebuilds. Tightening this screw will simply lock the pointer. No need to touch it unless you are removing the pointer, which shouldn't be necessary. Good hunting. Cheers
Peter TD 5801
P Hehir

The ammeter on the TD id very rudimentary. There is a single hairpin loop connected to the terminals and an iron vane suspended inside the loop connected to the outside needle. As current flows it creates a magnetic field which rotates the vane and thus the needle.

The current path is through the heavy wires, through the lug/stud to the inside of the meter, through the hairpin loop, through the stud/lug and through the heavy wire.

If the circuit is intermittent, and the wires are firmly secured to the lugs and the lugs are tight on the studs, you may want to remove the meter, take it apart and look at how well the hairpin loop is secured to the studs on the inside.

Jim B.
JA Benjamin

IF - IF the TD/TF can run without an ammeter in the circuit, by-pass it until you can have it fixed or replaced. I don't give mine a whole lot of attention.

The MGA doesn't have one, I think it's basically the same electrical system.

Anyone.....?
MAndrus

Careful-- The main wire to the ammeter is hot all the time when the battery is connected(It goes to the hot side of cable pull start switch). Any time your behind the dash, please disconnect the battery or smoke and sparks will ruin your day.

The ammeter could certainly be the problem. If it has been exposed to weather and wet conditions in the past, the internal connections could be corroded or loose enough to cause intermittent connections. (See the photo of copper loop and rivet attachment points).
A photo gallery of a disassembled instrument can be seen at web page: http://www.ttalk.info/Amp_Meter/

The ammeter is held in the metal dash center panel by some small tabs that are bent out to secure it. To remove the gauge those little tabs must be pushed in just enough to allow the ammeter to come out of the panel.

Disassembly of the ammeter isn't hard, but its a delicate operation to accomplish without bending the needle, and if the face or bezel condition is below your standards, it easier to let someone like "From The Frame Up" do the work.

Richard Cameron


Photo of little metal tabs (I think 4 each)

Richard Cameron

There are 4 tabs. These are on the original LUCAS BM 4 ammeters. If these are broken it is possible to alter the means of attachment so a 'U' bracket can be fitted. I'm about to modify one of mine so I can do just that, using a forked head, a knurled nut & some threaded rod. The one in my dash is not original & uses the 'U' bracket. This is a mounting point for the harness earths so I plan to reuse it. I agree with Jim & Rich on confirming that the two internal solder joints are secure. Continuity can be checked with an ohmmeter. The face can be easily refreshed using a decal. Much cheaper than having someone else do it. Pic of disassembled instrument below. It is not necessary to remove the top pivot mount. The small screw is the bottom pivot mount referred to in my first post above. The pivot in the foreground from my other ammeter has a broken pointer. Cheers
Peter TD 5801

P Hehir


I bought my ammeter bezels and glass, through this company in England. Parts were very good, reasonably priced, and they shipped to US without problems.

http://www.autoelectricalspares.co.uk/010154-bezel--case-for-lucas-bm4-ammeter-tag-type-2895-p.asp
Richard Cameron

Hi

Why not take it out of circuit and see if the problem goes away. Make sure you disconnect the battery first then join the two ammeter wires together with an insulation block. That will give you a chance to run the car and give the instrument a thorough check.

Barry
B Bridgens

No need for a block - just put both wires on the same terminal of the ammeter to rule out the instrument.

Chris at Octarine Services

it's a real pain to take the ampmeter out so I'd test it first. You can bypass it by just taking off one of the wires ( either one) and putting it on the other terminal and then screwing the removed nut onto this terminal. If everything works you will know that the problem was in the ammeter. You can easily hook up a voltmeter to this terminal to get you by till you tackle the removal job.
cj schmit

Glad to see that the bezel/cases have finally been reproduced. O'Connor used the screw from the inside of the case years ago, but as cheap as the bezels are better to just replace it. All advice good.
George Butz

Let me apologize for the senior moments that had talking about the posts on the ammeter. I'm so used to ammeters with posts that I totally forgot that ours have screw terminals.

Looking at the WSM wiring diagrams I can see an easy way to bypass the ammeter -- if your '52 has a 5-post regulator. Connect a jumper wire (14 gauge) between terminal A1 of the fuse box and terminal A of the regulator. This provides a shunt directly across the ammeter, taking it, and its connections, out of the circuit.

Bud
Bud Krueger


Bud, that's a smart and easy recommendation to isolate J.A's Ammeter or target it as the culprit one way or the other. I hope he appreciates your wisdom after a senior moment earlier.
Richard Cameron

Thanks to all for the help and direction to isolate the trouble with the ammeter. I will cut the ammeter out of the circuit this week. Hopefully that will get me back on the road. Will advise all of the results. Don't worry Bud, I have plenty of senior moments,.
Jeff
J.A. McWhirter

Just don't use the word CUT. Move one wire to the other is a better way to put it.
:)

M Grogan

Looks like the trouble is in the ammeter. The back of the ammeter is cracked where the wires attach, causing the circuit to go open. Any recommendations on someone to repair or rebuild?
J.A. McWhirter

Best to remove it and see if you can make a repair to the body with epoxy adhesive. At the same time check that the innards can be repaired. These things are incredibly simple from what I remember. A heavy bent wire carries the current and the magnetic field causes the deflection of the pointer mechanism. For safety sake make sure that the terminals are secure and firmly attached to the bent wire. You don't want any risk of a terminal touching anywhere its not supposed to or there is serious risk of fire.
Dave H
Dave Hill


Recommend you call Doug Pelton at Frame UP. Tell him what your problem is and what you want done--i.e. a full rebuild/restoration or just a repair. I have had good luck with the company and they seem really good about working custom deals for individual situations.

https://fromtheframeup.com/
Richard Cameron


Also-- One on EBAY? Looks like it will need some work also though, #292113078924
Richard Cameron

I agree with Dave. It's an incredibly simple & basic instrument. If it can be repaired you should easily be able to do that yourself. Bud Kruger's thread in the archive 'Refreshing 30 amp ammeter' will give you all the information you need, with plenty of pics. Curious as to whether the 52 had changed over from the 20 amp to the 30 amp version & does anybody know the date/chassis number of the change?
P Hehir

JA--- Did you remove it from the dash yet? If so please post a picture of the cracked area.
Richard Cameron

Peter,

Recently I asked Chris Couper the question about the change from 20/20 to 30/30.

This was his answer:

<quote>
I don't know. Might just have been a standard upgrade because other cars using the same part needed it. For example cars started getting heaters and radios so the power draw was larger. Both of these were options on the TD and they might have felt it was (would be) needed.
<unquote>

Jasper
Jasper Nederhoed TD3966

Change occurred at TD 10751, same time as flat to dished face speedo and tach according to "The T-series Restoration Guide" from the NEMGTR.
George Butz

Thanks Jasper. I'm attempting to compile info for Chris on the evolution of the TD dashboard instrumentation & switches. Obviously the collective knowledge here is a valuable resource particularly those with one owner cars or cars that belonged to a parent. Green, Schact & TSO Handbook are also useful sources. Apologies for bending your thread JA. Cheers
Peter TD 5801
P Hehir

This thread was discussed between 06/05/2017 and 15/05/2017

MG TD TF 1500 index

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