12V line for twin cdm's...

giguchan · Post by **giguchan** » Sun Oct 10, 2004 6:56 pm

Hey,
I'm almost ready to install my cdm's I have been hearing about installing a relay in the 12v lines..should i go straight to the battery or another source?i wont be doing any monitoring or transmitting while the vehicle is off.what purpose is this relay?
thanks gig
n2jhs

wa2zdy · Post by **wa2zdy** » Mon Oct 11, 2004 12:54 am

Positive lead straight to the battery, with a fuse right at the battery. Negative lead to chassis ground as close to the radios as you can get.

Relays and such are installed for folks who worry they'll forget to turn the radio off and will run down the starting battery, or folks who have second batteries installed and want them isolated from the starting battery while the engine is shut down, etc.

If you can remember to turn your radios off when you park for extended times (like over the weekend) you can just wire them the simple way - to the battery.

apco25 · Post by **apco25** » Mon Oct 11, 2004 1:04 am

or you just like your radios to turn on and off with the vehicle ignition.

Lord Windeshmere · Post by **Lord Windeshmere** » Mon Oct 11, 2004 5:31 am

Just like the Maxtrac and GM300 there is a pin on the accessory connector on the back for ignition-switched sensing. No need for a redundant relay.
Also, fuse the GROUND and HOT leads. The fuses should be no more than 6"-8" away from the end connections(power sources).

nmfire10 · Post by **nmfire10** » Mon Oct 11, 2004 7:00 am

Yes, use the ignition sense pin on the accessory connector to have it follow the ignition. You can program it to allow manual overide using the power button to use the radio with the car off or turn the radio off with the car on.

I was always told to never fuse the ground. If the ground fuse pops for whatever reason, it will seek out a ground through something else and cause damage. Hence, the power cord from Motorola only has a fuse holder on the (+) lead.

jbxx · Post by **jbxx** » Mon Oct 11, 2004 7:10 am

This question has to do with fusing the ground.
Is this only neccessary when going directly to the battery
negative? I am under the impression that this is to provide
a safety factor in the event that the bond between the
batt. negative and the chassis opens, thus using the
radio neg. wire to conduct say, the starter current.
If you go to the frame, do you still fuse the negative?
J.B. AD6WX

MassFD · Post by **MassFD** » Mon Oct 11, 2004 12:40 pm

In that case I would fuse the ground, would not want starter current to find it's way to ground via the radios power cable. Bet that would blow some traces on the board!

I would not recomend you bring the radio ground to the battery for that reason, take the radio ground to the chassis and check that the battery ground cable goes to the engine block to supply the starter ground and that their is a good bond jumper from the engine block to the chassis.

Lord Windeshmere · Post by **Lord Windeshmere** » Mon Oct 11, 2004 12:53 pm

You could fuse & ground to the battery terminal or to chassis with no fear. Anyone doing installs should always check anyhow that the battery is grounded to the chassis. My installs have always been either chassis or battery terminal and either way I've NEVER had a problem.

n3kvp · Post by **n3kvp** » Mon Oct 11, 2004 1:25 pm

One good thing about hooking both positive & negitive leads right to the battery is that the battery acts like a big filter capacitor to reduce any alternator a/c ripple/whine.

giguchan · Post by **giguchan** » Mon Oct 11, 2004 6:28 pm

MANY THANKS!!!!
I was alwasy told the you should go right to the battery(fused) Never heard of fusing the neg... but i guess it makes sense... But since I never had any problem doing it the old fashioned way thats the way i'll do it..The only reason I asked was the radios are new and i guess i have new radio jitters, Besides i thought i heard somewhere here that a fellow had problems with his maxtrac or cdm and a 12v line.. did something to the radio... but thanks anyway for ALL of the replies... I'd show you pics of the install but by the standard i see here I don't want to embarass my self.(with my installs or my spelling) supposed to be getting a new company vehicle(chevy trailblazer) so it might be temp.. i hear they are quite challenging.
...
thanks.