40mopar Posted August 5, 2017 Share Posted August 5, 2017 Was messing with the ignition switch bezel on my '52 MG because it was loose. Like an idiot, I didn't disconnect the battery. Experienced a few sparks and smelled smoke. Stopped immediately, but now I have no lights and no spark to the engine. The needle on the ammeter is now pinned at -30 rather than being at 0. Starter works and horn works. No fuses seem to have blown. Don't have a clue where to start looking for the problem. Help. Link to comment Share on other sites More sharing options...
Rusty_OToole Posted August 5, 2017 Share Posted August 5, 2017 Suggest you start with the ignition switch. Look for burned wires on the back. Disconnect the battery first. Your ammeter is toast. That should not stop the car from running. They do have a fuse on the back of the ignition switch if I recall rightly. Check fuses first, then look for burned wires. Link to comment Share on other sites More sharing options...
JACK M Posted August 5, 2017 Share Posted August 5, 2017 Jump across the ammeter to see if it may be open. Link to comment Share on other sites More sharing options...
40mopar Posted August 5, 2017 Author Share Posted August 5, 2017 Don't see any fuse on back of ignition switch. Fuses at voltage regulator are ok. No burned wires that I can see. Not quite sure how to jump across ammeter. Link to comment Share on other sites More sharing options...
mike6024 Posted August 5, 2017 Share Posted August 5, 2017 (edited) I think the ammeter has a built in shunt resistor which is probably burned out due to current overload, which would explain why it is pegged at max current discharge. But like was mentioned that would not prevent the car from starting. Do you have a wiring diagram? You have no voltage getting to the coil? Think about what might be burned out by tracing through the wiring diagram how 12 volts should make it's way to the coil, and where the problem may be. And use a volt meter to test at various points along the path. Not sure if this is the correct diagram, it is in pdf format. http://www.mossmotors.com/graphics/products/PDF/357-068.pdf Here is a supposed '52 MG diagram, unreadable though. Edited August 5, 2017 by mike6024 (see edit history) Link to comment Share on other sites More sharing options...
oldford Posted August 5, 2017 Share Posted August 5, 2017 You shouldn't have to jump across the ammeter. The ammeter is a dead short with a sensing wire that samples the current. Most likely, the lighter sensing wire is burned open and this is what causes the ammeter failure. If the shunt has failed, you will see melted wire on the back of the ammeter. Frank Link to comment Share on other sites More sharing options...
capngrog Posted August 5, 2017 Share Posted August 5, 2017 Click on the link furnished by Mike6024 above, and you'll see that everything in the car, with the exception of the starter and the horns, is fed through the ammeter. This is typical for many older cars, and I encountered a similar situation when I re-wired one of my Crosleys. I know little about electricity, but what oldford said above sounds about right, but who knows how a British ammeter is set up? Check for continuity between both poles of the ammeter, and if you have it, your problem is not the ammeter itself, although the current measuring capability of the gauge may be "toast". Looking at the wiring diagram furnished by Mike6024, it appears that power is fed from the ammeter to the voltage regulator, and then to the ignition/light switch. This seems a little strange to me, but, as I said, I don't know that much about automobile electrical systems. Perhaps someone on this forum having more knowledge than me can take a look at Mike 6024's diagram. I understand that the major components of your MG's wiring system are of Lucas manufacture. Good luck with your efforts and let us know how you make out. Cheers, Grog Link to comment Share on other sites More sharing options...
mike6024 Posted August 5, 2017 Share Posted August 5, 2017 3 hours ago, JACK M said: Jump across the ammeter to see if it may be open. This means remove the wires from the back of the ammeter and connect them together. Brown wires connected to one terminal (going in?) and a brown/white wire on the other terminal coming out. So jump means connect the brown to the brown/white directly. This way if the ammeter is fried you will be bypassing it. Link to comment Share on other sites More sharing options...
TerryB Posted August 5, 2017 Share Posted August 5, 2017 In the good old days of analog gauges it was not unheard of wrapping the gauge needle around the stop pin at the extreme ends of the gauge range. Terry Link to comment Share on other sites More sharing options...
HarryLime Posted August 6, 2017 Share Posted August 6, 2017 Once you let the smoke out of a Lucas system, it's just too hard to repair back to original. 1 Link to comment Share on other sites More sharing options...
R Walling Posted August 6, 2017 Share Posted August 6, 2017 Are you really wondering why your electric system in not working? Come on, it's a Lucas system! Link to comment Share on other sites More sharing options...
Guest BillP Posted August 6, 2017 Share Posted August 6, 2017 12 hours ago, 23hack said: Once you let the smoke out of a Lucas system, it's just too hard to repair back to original. There is a fix for that. Link to comment Share on other sites More sharing options...
padgett Posted August 6, 2017 Share Posted August 6, 2017 (edited) Many edits as some little used synapses relating to an MGA I had a long time ago fired. As mentioned inside the circuit is a 30A shunt resistor that is almost (but not quite) a short. The ammeter itself is a low current (like 1 ma) device that measures the drop across the shunt resistor. If the resistor opens, the meter will peg but nothing will work. 40: Does the 52 MG have a 12v battery ? The .pdf is much better but looks like the shunt resistor is inside the "control box" (regulator ?) and not the ammeter. If so the wires to the ammeter will not be overly large. Also the starter switch (looks mechanical - is it a pull knob on the dash ?) is directly between the battery and the starter so should work (cranks but no fire). If mechanical there may not be a solenoid. ps looks like with a blown regulator, there will be no power on the AI (lighting and ignition) regulator connection. E should be ground. Edited August 6, 2017 by padgett (see edit history) 1 Link to comment Share on other sites More sharing options...
Uncle_Buck Posted August 6, 2017 Share Posted August 6, 2017 3 hours ago, BillP said: There is a fix for that. And if your local dealer is out of this popular product, be sure to check out FeeBay for this product, Best Offer, Auction ends soon ... 1 Link to comment Share on other sites More sharing options...
padgett Posted August 6, 2017 Share Posted August 6, 2017 I never had any problems with Lucas systems and had some advantages: - was very easy to open the drivers door of my 150 & hit the fuel pump with a spanner if it didn't tick. - to hotwire a '50-'60s Rolls you just needed to move one fuse - to add a Delco alternator, you just needed to reverse the diodes. Italian wiring OTOH... Link to comment Share on other sites More sharing options...
40mopar Posted August 7, 2017 Author Share Posted August 7, 2017 After studying the above posts and looking at the wiring diagram I think I understand. All the power goes through the ammeter and regulator first, then to the ignition/light switch, so if one is bad, nothing gets to the switch. The wires on my car are color coded as described, so today I will try to jump across the ammeter and have ordered another control box just in case. Only problem now is how to physically get to those wires. Thanks everyone for the help. Link to comment Share on other sites More sharing options...
40mopar Posted August 7, 2017 Author Share Posted August 7, 2017 Ok, finally got the nerve to try this. Got the two wires off the ammeter. Checked the one coming from the battery and had 12v, so it's ok. Connected the two wires, then went to the control box. Had 12v at the terminal with the wire from the ammeter, so that wire is ok, but no juice at the other terminal, so I assume the voltage regulator is shot. Is there any other way to check the voltage regulator? Also, when I disconnected the ammeter, the needle went back to neutral. Any way to test it and can it be rebuilt? Thanks Link to comment Share on other sites More sharing options...
MCHinson Posted August 7, 2017 Share Posted August 7, 2017 If the needle went back to a neutral position when you removed the wires, it sounds to me like your Ammeter might be OK and only the voltage regulator needs to be replaced. Link to comment Share on other sites More sharing options...
padgett Posted August 7, 2017 Share Posted August 7, 2017 "All the power goes through the ammeter " I do not think so. Are the wires to the ammeter much heavier (like #10) than the other wires ? If not it is just sensing the load and not carrying it. Link to comment Share on other sites More sharing options...
40mopar Posted August 7, 2017 Author Share Posted August 7, 2017 39 minutes ago, padgett said: "All the power goes through the ammeter " I do not think so. Are the wires to the ammeter much heavier (like #10) than the other wires ? If not it is just sensing the load and not carrying it. Wires are heavy...at least #10. Link to comment Share on other sites More sharing options...
Ronnie Posted August 7, 2017 Share Posted August 7, 2017 I just looked at the wiring diagram you provide in the .pdf. The heavy wires on the ammeter connect to the voltage regulator and the battery. The ammeter appears to be in the battery charging circuit. Since the ammeter is reading a negative value I suspect a bad regulator - Or if you didn't find any burned wires or bad fuses and the regulator is good you might need to polarize the generator/voltage regulator after the sparking episode at the ignition switch. I'm just trying to think of something that would cause the ammeter to read a negative value. Link to comment Share on other sites More sharing options...
40mopar Posted August 9, 2017 Author Share Posted August 9, 2017 Got my replacement control box today. When I took the old one off I just happened to look at the bottom. Little metal strap that carries the incoming current was burned out. Hooked up the new box and have light and the car starts. Man what a relief! 2 Link to comment Share on other sites More sharing options...
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