hattymender Posted May 31, 2008 Share Posted May 31, 2008 110 engine swap. 3.5 V8 on carbs fitted. Bulkhead (and harness) from diesel. Harness matches. Engine runs. Oil light goes out. All's well. Except the ignition light. It's driving me nuts! Nothing, zero, zip & squit diddly. No light whatsoever either before or after starting. I've checked and swapped the bulb. There's continuity in the engine harness. There's 12v at the panel light multi-block. But absolutely no ignition light. Now here's the thing. I never figured out how the ignition light worked. Light going off when there's voltage is counter-intuitive? I can see there's a ballast resistor between white wire (ignition +) and brown/yellow (ignition light). But could somebody explain? And even better explain why mine does s#d all? Cheers Quote Link to comment Share on other sites More sharing options...
hattymender Posted June 1, 2008 Author Share Posted June 1, 2008 A long study of the wiring diagram in the smallest room (chamber of learning?) and I think I've sussed it. Ignition light takes 12v from the white wire when turned on. Alternator is not doing anything so all the wiggly amps flow down hill to earth through the brown/yellow and alternator. When the alternator wakes up it makes 12v + and pushes the wiggly amps back so it's = across the light. So the light goes out. Now I have 12v at the brown/yellow. I thought that was good. Now think it's bad. Should be 0v. So somewhere I have 12v getting onto this line. Investigations continue................ Quote Link to comment Share on other sites More sharing options...
Kim Horsevad Posted June 1, 2008 Share Posted June 1, 2008 A long study of the wiring diagram in the smallest room (chamber of learning?) and I think I've sussed it.Ignition light takes 12v from the white wire when turned on. Alternator is not doing anything so all the wiggly amps flow down hill to earth through the brown/yellow and alternator. When the alternator wakes up it makes 12v + and pushes the wiggly amps back so it's = across the light. So the light goes out. Now I have 12v at the brown/yellow. I thought that was good. Now think it's bad. Should be 0v. So somewhere I have 12v getting onto this line. Investigations continue................ Your explanation is correct. The alternator needs current input from battery over charge warning light to D+ on alternator. On startup the regulator shorts the field windings and D+, thereby making current flow. This turns on the ignition light, as a current flows through it. When the field windings are energised the alternator begins to produce current, and D+ is effectively coupled to B+ (main output from alternator). Therefore the charge warning light recives no current, as there is no difference in the electrical potential on each side. To make a charge warning light, you would want to locate som ignition switched supply, connect a 2 watt bulb and run a wire back to D+ on the alternator. Make sure the supply is ignition feed - else the bulb will be on whenever the alternator is not charging (vehicle at standstill) Quote Link to comment Share on other sites More sharing options...
hattymender Posted June 1, 2008 Author Share Posted June 1, 2008 10 cigs and three cups of coffee and we have a result! Bad earth on alternator. Quite why it was bad I don't know, joints tight and clean. But a rub with emery paper and the light came on. Now to the next problem................................. Quote Link to comment Share on other sites More sharing options...
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