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no brake lights /coil get real hot

Posted by sawshahall 
chuck Hall
charleston, WV, USA   usa
1972 MG M-type Midget "Mary"

Hello Guys
I have the 72midget. Thanks so much to all of you that contributed in getting my car started. Now I have another problem. I lost my brake lights and noticed tonight while car was runing I ws trying to trace down the wireing starting with the brake lights first. No luck. I noticed that I had point one headlight that is now staying dim bought new hgeadlight no change but when car was runing the coil got real hot. I placed a test light on the four fuses the first two fuses had power s litlle while later I tested the fuse box and all four fuses had power. i shut down the engine then try to start would not turn over. I still have signal lights backup lights thats it. Im confused I dont understand which way to go.
Need guidance

Thank you
most greatful
chuck
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Kerr Avatar
Norm Kerr
Ann Arbor, Mi, USA   usa

this is a challenge, because each of these are fed by a different circuit (there probably won't be one, single cause)

my suggestion is to follow your initial impulse, which was to trace the wiring all of the way from the item to the battery

the brake lights are powered by the green circuit, so if the turn signals and the tach works then the issue must be somewhere farther downstream. I would recommend you test the brake light switch (remove the cover from the pedal box and test for power there, and test the switch operation). If that switch has power, and functions properly, then I'd look for a cut wire between there and the tail lamps. Also, the tail lamps are grounded by the body attaching nuts, check that your tail lights work with a known power supply (run a long wire from the battery, to the wire connector near the tail lamp and see if it lights up, if not, then your problem is a bad ground). I suspect that your problem is power supply, not ground, because you said that they are both out (each is grounded separately).

The low beams issue could be a bad ground (they are grounded by a black wire screwed to the inner fender on the RH side of the engine bay, and there are a couple of connectors between the headlights and there. Check these first. If you confirm that the headlights work fine with a known power source (run a wire directly from the battery for a moment to supply directly to the back of the bulbs), then I'd suspect the power supply. The low beams are powered by the ignition switch, directly from the battery (no fuse) so it could be that, or the light switch on the column. Test them both (pull the wiring down from behind the dash/steering column cowling, and test the wires at the connector with a known power supply and operate the switch). The power to the ig. sw. is brown (battery +12V), and the wire from the ig. sw. to the light switch is blue, and from the light switch to the low beams is blue/red. If power is present at the in-line connectors, then trace the blue/red wire to the headlights to find the fault.

the high beams have their own supply, so you can see if they still work, to help trace where your wiring faults are with the low beams (they have separate power supplies, but share the ground

A hot coil can mean a bad ground inside of the distributor, or the polarity is swapped on the coil, or it is going bad internally.

Norm
hoggie Avatar
Mike Hogan
Oklahoma City, USA   usa

Chuck, as Norm indicates, you probably have multiple issues which makes you go crazy because you are trying to relate them all to the same cause which may not be the case. I have found the best way is to pick the most obvious issue, like no brake lights, and focus on that problem ignoring the others. I think on this car, you have to have the ignition on to power the brake lights, so you probably want to disconnect the distributor to coil battery lead so you won't be pulling current through the coil or burning the points while your trying to trace the brake light issue. That may be why the coil is heating up with your current testing. Normally the coil only pulls current intermittently as the points open and close. Do you have access to a good diagram ?
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Kerr Avatar
Norm Kerr
Ann Arbor, Mi, USA   usa

here is a link to the wiring diagram, '72 is diagram 12

http://www.spritespot.com/Downloads/Workshop%20Manual/Z%20Appendix.pdf


Norm
chuck Hall
charleston, WV, USA   usa
1972 MG M-type Midget "Mary"

Hello Norm and mike

I have been working on my mg today I have made some progress the headlights I started on them today. Well you were correct I started at the front fender snd started moving around some wires the headlight that was dim really brightened up then it got hot but after making a new connection thay are working. One down two to go. I checked the brake light switch it had power on it you said take of the plate cover off of the box and test there are these two different things because my switch sticks out throughthe box to the outside. I had mentioned that my turn signals work great and park lights also backup lights work you had mentioned in your last e-mail that my tac was working but it 's not working. I used test light under the dash the wires going to the tac had power also checked the ignition wires on the column three of the connections on the stearing column light up out of the four. i believe that is correct. When I try and start the car the key is onthe red light comes on after the key is at the on position nothing not even a noise. I crossed it over under the hood turned on the key used my remote started it atarted right up. I put a test light on bot sides of the solenoid there was power. So tomorrow I will run a wire from the battery back to the lights and check for power there. I turned on the key to the on position used my test light after removing the back lens no power.
I dont mean to be so long on the conversation but Im trying to learn how these are connected or not.

Thanks again
Norm/Mike

Chuck
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chuck Hall
charleston, WV, USA   usa
1972 MG M-type Midget "Mary"

Hello Norm:

I started testing some things on my midget. First I traced down the headlight that was dim. I fouund a loose connection on the right side of the wheel. So headlights work. Next I started tracing down the wires engine doesnt turn over when you turn the key in the start position. I had someone to hold the key in the start position while I placed a test light on the red/white wire that goes to the seioliod tnere was no power I placed the test light in the wire itself still no power.Now I went under the dash and placed a test light on the 4 wires to the ignition switch. Without the key in start position 3 out of the 4 wires would light up. When I turned the key in the start position one wire on the bottom of the ignition switch no power until I let up on the key then it would show power going to it. I did the same for the top wire and it would light up when I put it in the start position. Now my tacometer doesnt work but I checked power on the green wire and white wire they both had power. So is my solenoid bad? By not having power comming to the red/white wire?

Thanks

Chuck
hoggie Avatar
Mike Hogan
Oklahoma City, USA   usa

Your solenoid should be OK if you can place a strap from the battery side of the solenoid to the White/Red terminal on the solenoid and turn the engine. Check to see that the White/Red wire at the ignition switch is getting battery when you turn the key to start. If so, you might have a connector problem. The wiring diagram shows a splice connector on the White/Red wire at some point. Possible it has become oxidized and needs cleaning.
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Robert Kirk
Davenport, Iowa, USA   usa

Tracking down wiring problems is a royal pain in my book. But the coil issue as Norm indicates can also be a number of things. I'd make sure you have the proper internal ballasted coil used in that period. The wing dings at the corner parts stores who only advise via their computer aren't always the brightest lamps on the tree....



Regards,
Robert Kirk
kirkbrit@yahoo.com
563 323 1017
Moss distributor UK importer
Beat or match any retail/delivered quote

Member Services:
Parts for your classic British and Italian car. 30 years in business.
mjamgb Avatar
michael anderson
NORTHERN NEVADA, USA   usa

Once you have the engine running, check the coil. If it is still VERY hot, you may put it on your list to replace soon.

It is very common for a coil to get hot if there is power to it but the motor isn't running... bad for it. Incidentally, also bad for your points (if you have them) as they can weld together, should the engine stop at "just" that point where they are opening or closing, from a sustained arc.

Correct polarity is nice, too, but the same exact coil works fine with either negative or positive ground systems depending on how you hook it up. Totally mess up the connections and it just will not run.
1973 midget Avatar
Jim M
Really, Kansas, USA   usa

Mine was doing was doing the same thing. Even had a thread on it. Turned out to be the ignition switch. The contacts had melted at some point. Replaced and have had no problems since.
chuck Hall
charleston, WV, USA   usa
1972 MG M-type Midget "Mary"

Hello Gentlemen:

I got under my dash tonight I found the red/white was unpluged. When I put it back together it started right up. Now the headlights are fixed but now the coil is real hot after I have it running for a while. I have the white wire in the positive side of the coil and the black/white strip going to the distributor. Still no brake lights at this time. I tested the two green wires under trhe dash it had power. I checked the hot wire on the tack and its hot but tac not working. So Im looking at brake lights and coil getting real hot also the tac doesn't work but there is current going to it. Please advise

Than you Guys

Chuck
hoggie Avatar
Mike Hogan
Oklahoma City, USA   usa

Chuck, Your coil battery feed loops through the tach. That's how the tach determines the engine speed, by the frequency of the current flow changes to the coil as the points open and close. With the points open, no current should be flowing to the coil. If their is still current flowing to the coil with the points open, then your tach is not going to detect the changes and your coil is going to heat up. The white wire should be connected to the + positive terminal on the coil. You can insert a current meter at this point and look for current flow. If you see current, pull the white/brown wire off going to the + terminal distributor and see if the current stops. If you have any current with the dizzy white/brown wire pulled, then you probably have a bad coil. Most likely you will not see current flow after you disconnect the wire to the dizzy. Then the most common suspect would be the dizzy condenser. If the dizzy wiring or points were grounding, then engine would not run. Also for reference, your coil should have about 3 to 4 ohms resistance.
chuck Hall
charleston, WV, USA   usa
1972 MG M-type Midget "Mary"

Hello Gentermen:
Ok headlights working great loose connection. Mike you had mentioned that my coil battery feed loops through the tach. I ordered a tach should be here monday. Question I got the car running . I started it today I was going to take it for a spin. I was in the house for a few minutes the car just quit. I checked the fuel pump the glass fuel filter was full but didn;t want to fire at all. Later tonight I went out to stsrt it again started right up after it warmed up a little it just stop running. I tried as before to restart the engine turns good but wont star. Would this be tied into the coil being bad?still working on headlights

Thanks a lot

Chuck
hoggie Avatar
Mike Hogan
Oklahoma City, USA   usa

Normally I would think you have a fuel issue, but your coil is suspect if it is still heating up and pulling current with the points open. If it is fuel related, then your engine is either flooding or starving. Shoot a little starter fluid in the carbs and see if it will fire, or pull a spark wire, and see if you have any spark.
Robert Kirk
Davenport, Iowa, USA   usa

Chuck you need to be a little more inquisitive. As soon as the motor will not start, pull a wire to a plug and see if there is fire to the plug...if not, do the same with the coil wire...pull it from the dizzy cap and see if there is fire. Note the color of the spark..it its yellow (weak as opposed to blue/white) or nonexistant directly from the coil, you have a bad coil.



Regards,
Robert Kirk
kirkbrit@yahoo.com
563 323 1017
Moss distributor UK importer
Beat or match any retail/delivered quote

Member Services:
Parts for your classic British and Italian car. 30 years in business.
. You can hide this ad & support this site by upgrading to a Gold Membership ~ click here for more info

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