| Author | Message | ||
     Bob Reynolds Frequent User Username: bobreynolds Post Number: 81 Registered: 8-2012 |
The headlamp flasher was not working on my 1975 SS1. I just traced the fault to a faulty flasher relay. The relay was clicking but the contacts had bunt out and were not making contact. This got me thinking about why they had burnt out, and it has raised some interesting questions.  The most obvious question is why Rolls-Royce didn't put a relief relay in the Main Beam supply, instead of feeding the entire current for all 4 headlamps through the Switchbox, Dip Switch, Flasher Relay, and other components. Considering the number of relays in this car (some of dubious purpose) it's hard to understand why they didn't put one in the main headlamp supply - especially as the car has 4 headlamps. I looked in the handbook, and the specified (UK) headlamps at the time were 37.5W/60W sealed beams for the outer ones, and 75W for the inner ones. So the 4 original main beams consumed a total of 270W. At 12 volts, that is a current of 22.5 Amps. All 4 headlamps are fed through Fuse 4, which is a wire fuse of only 22A. How is this possible without blowing the fuse continually? Are my calculations wrong? Even with 4 modern halogen headlamps of only 60W, the current would be 20A, which is much too near to the nominal value of the fuse for comfort. No wonder they needed to add a Headlamp Safety Relay to switch back to dipped beams if fuse 4 blew. That looks almost inevitable! It would have made more sense to use this relay to power the inner headlights via fuse 5 and share the headlamp load between fuse 4 and fuse 5 (fuse 5 feeds the headlamp flasher circuit). |
