I an not prepared to put up with gratuitous insults when I am trying to assist. Sort things out in your own way.

Yes - can't have too many fuses in vehicle systems!

Andy wanted a relay device to switch on manually with a push button, and which would switch off automatically when the ignition was turned off. My diagram 1 does that - I have shown an auxiliary relay if the main one does not have a spare latching contact. If a purely electronic version of the latch...

I just googled "dynastart regulator" and found several sites offering modern electronic regulators. Perhaps a bit more expensive than what you had in mind, but when you factor in your time probably not so bad after all ...

I there is a spare contact on your relay you can use that (or another relay with the coils in parallel) to short out the manual push switch. That will give you the effect of having the push switch on until the relay de-energises when the ignition is switched off.

Most multimeters have an internal cell or battery which is used on the ohms ranges. I can well appreciate that trying to measure a resistance in a circuit which contains semiconductors (transistors, ICs, etc.) would give rise to different readings because of the applied voltage from the meter. Why n...

The maximum supply voltage for standard TTL is 7v, and the max input voltage is 5.5v. If you are going to use TTL in a car, it is essential to use a 3 terminal voltage regulator chip, such as the 7805 series. A simple (and very effective - I have used it on numerous occasions) way of obtaining a swi...

Try http://www.new-wave-concepts.com/products.html - I think this may be the software author's address. It may well be available as a download.

Should be OK - why not try the simpler circuits and see. You might have to adjust the values of the variable resistors in series with the LDRs, to get exactly the turn on/off range you want. The 741s may not work too well on a +5v power line, but you could always power the relay from +5v, and the re...

How about a magnet attached to a spoke and a reed relay on the frame or forks?