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MG MGB Technical - Radio w/ignition on

Hello,
Will it hurt anything to run the radio with the ignition in the 'on' position without the engine running? On my old system I had a switch I used which powered the radio when the car was off. I just installed a new system recently and left off the by-pass switch. Do I need to put it back on?
Paul
Paul S. Canup

That depends on the year of the car. If it's a MKI, with no 'Accessory' key position, you can burn up your points. Your coil and fuel pump will also be energized, so my answer would be to put the bypass back in.
Ken Lessig

I agree with Ken, having the ignition on for long periods without the engine running also cooks the coil. Don't really see that you need a bypass switch, just connect it to a purple supply or a brown one via an in-line fuse and turn it off when you don't need it. If you think you might forget to do that then you might forget to turn off the bypass switch just as easily.
Paul Hunt

I agree with Paul S. 99% of the time, you want the radio to turn off when you turn the ignition off, so leaving the bypass switch in the "ignition" position, you have that feature. The few times you may want to have the radio on with the engine off, flip the bypass switch over and you have it. You may still forget to turn it off, but the odds are not as high as if you had the radio wired to permanently bypass the ignition switch.

Just make sure you don't creat a "sneak" path, whereby power can sneak through the bypass switch and backfeed the ignition switch. I would use a SPDT switch, and wire the radio power lead to the center pin, the power feed from the ignition switch to one of the end pins, and the power feed from a brown or purple wire to the other end pin.

Maybe if you ask real nice, you can get Paul H. to design you a nifty little circuit like he did with the OD sequencing relay (a very clever design, btw), such that the bypass is automatically reset whenever you turn the radio off, so you don't have to worry about it the next time you start the car.
Dan Masters

You could put a hidden switch in the white to the pump and coil but take the radio feed from the ignition switch side. Only a simple on/off switch would be required, when you take the keys out the radio (and everything else) will always be off, and it is a simple imobiliser albeit easily defeated. The ignition warning light would still glow on early cars where they are wired direct to the switch but on others could also be disconnected depending on where you cut or interrupt the white.
Paul Hunt

This thread was discussed between 19/11/2002 and 20/11/2002

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