HUMBER SCEPTRE

CHARGING PROBLEM

Q

I am hoping you can help with a problem that has baffled my local auto electrician. I have a 1966 Humber Sceptre MKII which is fitted with the early type alternator and the 4TR control box. When there is a small positive charge rate, the ammeter needle and the lights will flicker rapidly. If the wires F and Earth from the box are joined effectively isolating the control box, the flickering will stop. It was diagnosed that the control box needed replacing which I have done, but the problem remains exactly the same with the new control box fitted. Does this mean that the alternator is at fault? Davin Edwards

A

My first check would be to see that all the connections are tight and that the problem is not due to something as simple as a loose terminal. I would extend these checks to not only the alternator and ignition wiring, but also to the battery and earth connections, including the engine-to-body earth strap.

The alternator fitted should be a Lucas 11AC, which also needed the 3AW and 6RA relays. It is feasible that one of these relays has developed a poor internal connection and the higher resistance is creating the problem that you have. You may be able to detect such a problem by feeling the temperature of the relays when the engine is running and the alternator is charging. If the relays are warm, then they are probably suffering from wear on the internal contacts.

The 6RA relay is still readily available, but a replacement unit is now made for the 3AW unit which is available from www.autoelectricsupplies.co.uk. The other alternative is to upgrade the alternator using diodes to eliminate the need for the relays. Details of this can be found by searching the internet for 11AC alternator guides.