MG Car Repair: Lost the taillights, inline fuse, fuseholder

Question
QUESTION: Hi Howard,

1968 MGB, GHN4 model.  My taillights just quit.  Brake lights work fine.  I inspected both the bulbs, and both filaments in both bulbs are intact.  I even measured resistances across each filament, and they seemed appropriate. Looking at the Haynes manual schematic it indicates that the taillights and headlights are fused, with red wires on both sides of the fuseholder.  I found two such fuseholders under the hood/bonnet on the right hand side, adjacent to the main fuse bank.  Unfortunately though, when I disconnected each fuse (separately, and both at the same time), with the headlights switched on, the headlights continued to burn, and of course the taillights were out.  My conclusion then was the fuses under the hood/bonnet are for something else, although I cannot seem to find them on the schematic.  What can you offer for me?

Thank you in advance, for any thoughts on the matter.

Regards,
Dan

ANSWER: Hi Dan,
If the front parking lights are working then the power from the light switch is good and it has to be a connector or an inline fuse. You may have to use your ohm meter to check for a connection from the tail light wire up to the connectors for the main harness to find where the power is interrupted at. I always preferred to run a temp power supply to a disconnected item then use a test light to find a fault in a circuit. I kept a fused test wire for that purpose and even put a warning buzzer and a light in it so if I blew a fuse while testing it would set off the buzzer and turn on the light to tell me I blew my fuse. It served me well for many years in dealerships. I see the in line fuses in the diagram but I don't remember where they were.
As I remember there are some connectors under the car at the fuel tank and then the next connectors are at the fire wall.
Leave everything turned off and run a power wire to the red connector at the first connector at the rear and just go to the pack of connectors at the fire wall and test all read connectors. That is how I would have approached the problem.
Howard

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

QUESTION: Hi Howard,

thank you for the prompt response.  The front parking lights are working.  I used an old computer power supply for a 12 VDC source, and chased down the connectors; they were mostly in the trunk.  It turns out the one of the two fuseholders I mentioned in the engine compartment (closer to the firewall, as you stated) was the flaky culprit.  Fussing with it seemed to improve the electrical connection; I wonder if I should just replace it.  I imagine the other fuseholder is meant for the headlights, however like I stated before when you have the headlights powered up, and disconnect the fuse, the lights stay on.  I almost wonder if my headlights are not fused; as if a previous owner disconnected them from the fuse?

Again, I appreciate the prompt, and valuable response, Howard!

Regards,
Dan  

Answer
Hi Dan,
I have found that many of the MGs were altered and there is no telling what changes have been made to the cars since new.

Every one including myself, made fun of Lucas electrics but even though their switches and relays were always the fault, the color coding of there wiring was always consistent and I was able to find and correct faults in British cars that we didn't have wiring diagrams because of the consistent color coding of the wiring.

If you ever have to work on the wiring of a Alfa or a Fiat you can appreciate Lucas of the British cars.
Howard