QuestionQUESTION: Barrie,
My 1980 MGB had an intermittant failure which has now become permanent. I have lost: tach, fuel & temp gauges, brake lights, rear lights, turn signals and heater. There appears to be no power going to the top three fuses.
Is this caused by the voltage stabiliser or something else?
Please help!!
ANSWER: Hi Ron
The top 2 fuses are for the sidelights. They will not be powered unless you turn the sidelights on (red wire).
Fuse #3 feeds all the circuits that you describe. It is fed from the ignition switch (white wire)so it is only live when the ignition is switched on. The voltage stabiliser only feeds the fuel gauge so that is not where your problem lies. My guess is that either the ignition switch is faulty, or there is a break in the circuit between the ignition switch and the fusebox. Try replacing fuse #3 before you do anything else.
/------------- MORE --------------/
There is another possibility, Ron. On a 1980 MGB all the circuits that you mention are wired via the ignition relay. Look for a black or blue canister hanging down with 4 wires going into it, close to the fusebox. The wires will be one Black, one Brown, and two wires which are Brown with a White stripe.
---------- FOLLOW-UP ----------
QUESTION: Update: I have confirmed that the fuse box is not the problem. If I switch the power wires from the bottom fuse to the affected circuit the affected instruments come back to life.
Checking with a circuit tester I find that there is no power in the two white/brown wires. I checked and there is power at the ignition relay ( there seems to be two of them-one on either side of the fuse box).
What should my next step be?
AnswerHi Ron. Unfortunately they used the same colour for these two Brown/White wires. One of them is very short and just goes from the relay to the fusebox. The other one is the actuator wire that comes from the ignition switch. The plain Brown wire provides permanent power directly from the battery and the purpose of the relay is to connect the Brown wire to the short Brown/White wire. The Black wire is an earth.
The Brown/White actuator wire should come live when you switch the ignition on with the key. If it doesn't come live then there is a fault probably at or near the ignition switch. You will have to drop the steering column (3 bolts) and remove the cowl (4 screws) in order to reveal the ignition switch. Check the multi-pin connector from the switch to the loom. These often go faulty. The switch itself can be replaced without removing the steering column lock. It is held to the back of the lock by one small grubscrew.
