MG Car Repair: Headlights and Tail lights do not work, fuse box, brown wires

Question
QUESTION: Howard, the clutch is working, the engine is running, I registered the car after 24 years of being off the road and not fine tuning the little things getting ready for the inspection and a surprise!! My headlights and tail lights stopped working. I must have done something when pulling the engine out. I know this is hard to do via notes but hopefully there is something obvious you can pint me to. I looks like the top and second fuses in the fuse box control the left and right heal/tail light circuits. I put a volt meter on the fuses and I am not getting power to the top two fuses. I have been looking at the schematics and trying to figure this out but thought there might a a relay or switch that controls this. Any thoughts? Where does the power to the fuse box come from? Can I jump a hot wire directly to the fuse box?

I know this is not an easy thing to work on this way so if it is too complicated a topic I understand. Hopefully there is something simple I can look at.

Thanks

ANSWER: Robert, look at all the brown wires as they are power supplies. The head light switch powers up the lights. Lucas is very good about color codes and what they do.
browns are power
blacks are grounds
whites involve ignition
purples are hot all the time
blue are head lights
reds are other lights
greens are accessories
When they use a colored stripe it is usually a modifier of the color for example, a green wire will operate an accessory and a green wire with a black stripe will be grounding operational wire for that accessory. Like a white wire is ignition wire and a white wire with a black stripe will be a grounding wire for the ignition system. This is general but it helps when trying to locate problems.
I would not even look at a car with an electrical problem without a wiring diagram. It is a basic and necessary tool to work on electrics.
You need to purchase a manual if you intend to keep the car.
Howard

---------- FOLLOW-UP ----------

QUESTION: The wiring color scheme will help. Thanks. I have a Haynes 1962 to 1980 Roadster and GT Coupe, 110cu-in Repair manual. I rate it as just "ok" in being helpful. Is there a book better than that one you would recommend?

ANSWER: I found that service manuals are not complete, even the factory manuals so I try to hang on to every manual I can. On some cars I have the Clymers, Haynes, Bentely and the factory manual and I sometimes have to refer to all of them. Generally I rate them as I have listed them. Not true in every case though. I also have a lot of the factory training booklets and bulletins. I plan to put them up on E-Bay soon. Other than trying to help people on this program, I don't work on cars for other people any more. I do have pet projects on a few MGs, Triumphs and Jags of my own. Even though I have a good background in British cars I still have to grab a manual to answer some of the questions on this program.

---------- FOLLOW-UP ----------

QUESTION: Hello Howard! Yes that color scheme on the wires has proven to be a BIG help.

I hope these follow-up questions with resolution are helpful to other readers.

As it is turning out, the electrical problem seems to be nothing more that all the contact/connections being so heavily oxidized that there is no connectivity. This car has been sitting in garages for 24 years so time has taken its toll. I just need to clean all the connections and one by one everything seems to be coming on line.

Two more questions (maybe three or four more over the next few weeks too!!). The brake light switch. Is it the switch on the master cylinder? My Haynes manual and catalogues from Victoria British and Moss (the diagrams in those vehicles have been the most helpful in figuring this all out!!) call that switch the “Pressure Fail Switch.” Nothing mentions the Brake Light switch anywhere in the manual or parts catalogues. Is this a dual function switch? The brake lights will light up if I connect the two wires that lead to the switch. If I order the replacement switch called a Pressure Fail Switch from the catalogues am I ok?

Thanks again for all the help!  

Answer
The Pressure Fail Sw. is the sw. on the junction block with all of the brake lines to it. When either circuit fails the difference in the pressure between the two circuits moves a piston over which lights the warning light on the instrument panel. As I remember your brake light sw is mounted on the cover of the clutch and brake pedals.
Yes, even the better manuals miss items. I try to keep one of each brand manual on the cars I still work with.
Howard