Team,
I have an LM-1 (wideband handheld computer). I am having serious issues getting good RPM data. Some claim this may because of "dirty" power noise.
I am running a new CS130 alternator which charges very well at idle.
The LM-1 comes with a cigerette style plug in. I used the factory plug for awhile and was getting some dirty RPM signals (pulled off HEI tach wire). I decided a wanted a keyed power sourse. And for other reaons besides the LM-1 I decided to put a hidden 12 volt keyed cigerette style 12 volt port under the dash. That way if I forget to shut the switch off my LM-1 I do not cook my O2 sensor all day.
Do get power to it, I tapped into my "accessory" terminal of the fuse block (after a fuse of course). However, just after the fuse I also splice, radio, voltmeter, 700R4 lockup and electric choke. This obviously can not be the "cleanest" 12 Volt signal. Any ideas how to get pure clean Volts to a keyed custom cigertte 12 Volt port?

relay ?

relay ?

I don't know much about relays. I guess I need to learn because I want to do some lighting upgrades soon and I know I'll need relays for that as well.

The relay would have power straight from th batt, or horn relay buss (12V constant), and then you would use the 12v switched to turn the relay on/off. You can set it so when your ign is on, it triggers the relay, turning on the 12V constant to your LM-1

The relay would have power straight from th batt, or horn relay buss (12V constant), and then you would use the 12v switched to turn the relay on/off. You can set it so when your ign is on, it triggers the relay, turning on the 12V constant to your LM-1

And in theory this would be a stronger cleaner signal than running off the accessory terminal? Its obvious it would be stronger, but would that give a cleaner signal?

And in theory this would be a stronger cleaner signal than running off the accessory terminal? Its obvious it would be stronger, but would that give a cleaner signal?

Yes I would imagine. the only items bewteen the car's main power point and your LM-1 would be the relay. Can't see it getting much better than that if you want it switched.