QuestionQUESTION: long story here but first thank you for all the help you have given!! got my 1977 mgb out this spring hooked the battery up an smoke came from under the hood i replaced the battery an it started right up . then we had a fire at home so i had to move it to storage . will when i started it to move the ing charging lite came on so i figured i must mave fired the alt. bought a brand new one the guy had to change the backs new one was a little diff so i come home hook it up an now it wont start it trys if u hold the key on an cranking it the second u let go it stops.i have have run continuity checks on lots of wires ones off the coil ect. i have a wire that comes off the same terminal on the coil as the white n green ones and goes to the bolt holding the coil.i check the wire its ok but there is a blue hard plastic head on the other end an when i check that no continuity. what is that for ? i tried to jump from that terminal to ground an the car wont even try to start then please help !!!!! ty mike whalen oshkosh wi usa
ANSWER: Hi Mike. What a sorry tale. Don't worry about the small blue plastic lump attached to the + terminal of the coil, it is just a condenser put there to suppress crackle when you listen to the radio. If you slacken the holding bolt on the coil, it should slide out because the bracket has a slot rather than a hole. Take it off and throw it away. If it shorts out, it can cause a fire.
The 77 B has a ballasted coil. Inside the wiring loom there is a pink resistive wire which I think has failed. It goes from the starter solenoid (on the starter) to the + terminal of the coil, and changes colour to white/green inside the loom. When you operate the starter, this wire is bypassed, but once you let go of the key the bypass wire is no longer energised, and a reduced voltage should be fed to the coil through the resistive wire. Just as a test, run a wire from the white side of fuse #3 direct to the + terminal on the coil. The car should run ok. You cannot leave it like that without changing the coil for an ordinary 12 volt coil. Basically, you have got an 8 volt coil at the moment, and it would overheat and burn out.
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QUESTION: Hi again i tried jumping from the + side of coil to #3 fuse nothing, when should that line turn hot ? i also noticed there is another relay on the fender well same numbers four terminals.could it be bad ? how do i check these ?this all started after changing the alt. think it could cause this ?
how can i check to see if the it self is not bad ? not sure that i mentioned i changed the ignition 28 years ago but it ran till i changed the alt. strang !! please i realy do thank you for you trying to help.please lets try again.i also noticed my tach an fuel gauge dont work??
ANSWER: That last bit of information is vital. It tells me that the ignition switch is not functioning properly, or the wire from the switch to the fusebox has failed. When you hit the starter, a separate wire is energised directly from the starter solenoid to the coil, bypassing everything in between. Once the engine is running and you release the key, that connection is severed and the engine then dies.
To check out the ignition circuit, connect the coil + to the brown side of fuse #4. The engine should now start and run on the key, but you will have to pull the wire to stop the engine.
Before you mess with the ignition switch, check out the wiring. Have a look at the two black plastic connector blocks between the switch and the fusebox. One is located about 6 inches away from the ignition switch, under the dash. There will be a bunch of them. Look for the one with 4 plain white wires going into it. Pull each bullet connector from the block, clean them and replace them. If the block looks as though it has overheated or the metal bit inside is corroded, then replace the entire connector block. They cost less than $1 each. The second connector block is in the engine compartment, near the bulkhead. It usually has 3 white wires going into it.
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Just looked at the wiring diagram. You have a relay that might be the culprit. It has 4 wires going to it, coloured Black, Brown, White, and White with a Brown stripe. They often play up. Usually located on the inner wing near the fusebox. Get someone to turn the ignition on while you hold the relay between your fingers. You should feel it click. My guess is that it will do nothing.
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QUESTION: Hi again i have a new relay had my son help he said he felt no click so he took it apart an now i have a new one but dont know how it goes back together !!! we forgot to mark down the position of the wire 85 86 87 30 are on the new one and the book shows c1 c2 w1 w2 ? could you please tell me why my tach an fuel gauge dont work now either ? also i replaced the alt. could it have anything to do with this trouble ? thanks again please lets keep trying all these things will save me alot of money.
AnswerRelay wiring is: Black to 85. White to 86. Brown to 87. White with brown stripe to 30.
If the relay still doesn't click, than you have a wiring fault, probably between ignition switch and relay. Use a voltmeter and check the switch has 12 volts to brown (input) and 12 volts to white (output). Be careful, because the brown wire is permanently live.
Tacho and fuel gauge are powered via fuse #3 and this relay activates fuse #3. Check that the heater fan still works ok, because that is on the separate extra line fuse below the fuse box.
