MG Car Repair: 1978 MGB ignition wiring, mgb gt, fuse box

Question
Hi Howard,

I recently bought a 1978 MGB GT, it broke down within two hours of collection with what appeared to be an electrical malfunction, due to a lack of power to the fuel pump. Upon closer inspection I have determined that the battery and alternator are both fine and the fuses/fuse housing under the bonnet are in good order. When the ignition is turned to position 2 there is no voltage on the fuse which protects the fuel pump, brake lights, windscreen washers etc, however the engine will still turn over, but obviously, not start. I am something of a newbie when it comes to classic cars and having checked the fuses am a little stuck as to what to check next. Do you think it could be an ignition problem at the key end, or is there a common fault on these cars which affects this particular circuit. Any advice you could provide would be great, as I'd much rather learn how to fix and maintain this car myself, rather than pay for someone else to do it.

Many thanks,

Gregg

Answer
Hi Gregg,
That fuse is powered by the ignition switch relay. To confirm that is the problem, run a temporary jumper in the fuse box to the dead fuse to see if everything operates. If so disconnect the the jumper and put a 12v test light on the white wire at the plug of the ignition switch. Turn on the ignition and if the white wire lights the test light, it tends to confirm that the problem is in the relay. (providing that the black wire at the relay is a good ground)
Sometimes you can strike a relay with a wrench and bring it back to life, if not, you can pry the cover off and clean the contacts with a points file.
Howard