powering up a headunit

[n0obi]

I was at a mates place yesterday and we tried to power up a headunit just to make sure it worked before installing it. We connected up the red, yellow, and ground, should have powered on right? We did that and it wouldn't power on, we did that in my mates car and it powered on. It's got me confuzzled :confused:

[Bol]

Did you connect to an accessory power - therefore only working when the ignition is on...?

[n0obi]

I did have the ignition on when testing to see if it worked. The unit wouldn't power on.

[Bol]

Ok...

So assuming that you connected the wires correctly, and that the unit does in fact work then there seems to be a problem with the wiring in the car. Just grab a test light and make sure both power wires work and that the ground also works.

Also, double check which is constant and which is ignition because if the are switched it isn't going to work.

[n0obi]

I'll have to try that when I get home tonight.

[noodleman27]

have you check the radio fuse?might be blown so no power going through the red wire

[n0obi]

I tested the ignition wire that reads 12.4V so that looks alright, but when I test the constant I get a reading of 3V if any reading at all.

So I hooked up ground + ignition, turned the ignition but get nothing. Do I have to have the constant hooked up also to get some activity or should I have got "something" from hooking ground+ignition ?

[stoney]

you need to have all 3 wires connected at the same time. if you are only getting 3 volts constant than you probably have a faulty fuse (burnt, but not blown). if you cannot find the fault than run another wire to another constant power source.

NOTE: finding the fault is important as it may cause other problems.

[Fhrx]

If both the red and yellow are receiving 12 volts and the black is against a solid earth then yes, the deck will power up.

[n0obi]

That would be the radio/lighter fuse right ? I checked it last night but it was a bit dark, what I saw was that it was a 30, but the diagram says it should be a 15. Maybe i'll have some better luck today/tonight.

[Fhrx]

If it should be a 15, put a 15 in it! Don't ever chuck a larger fuse in dude.

[n0obi]

If it should be a 15, put a 15 in it! Don't ever chuck a larger fuse in dude.

I didn't, i'm thinking the previous owner did for his system install. I'll double check the fuses today after work or during work.

[Fhrx]

That's cool then. Many of the wires in the car cannot handle 30 amps continuous and the last thing you want is your dash going up in flames when things start to burn. :(

[n0obi]

Ouch no we don't want that to happen.

[n0obi]

I think I give up something is obviously not right. I've done a couple of HU installs before, but they've all gone smoothly. Can anyone advise which wires go to where just to confirm i'm connecting the right ones.

I'm connecting the accesory/ignition to yellow with red stripe; battery/constant to white with blue stripe; and black to black of course.

Didn't get to check the fuses today because I got home too late and it was dark, but my mate said he swapped the 30A fuse with a 15 that was a spare in my fuse box.

[n0obi]

Found the problem. The wire I thought was the 12v constant wasn't it, there had been another wire (grey in color) that the previous owner has connected direct to the battery through a fuse. The reason why I wasn't getting any reading from any wires for a constant 12v was because the fuse was blown. Changed the fuse, everything's all hunky dory now. Only concern I had was that they used a 20A fuse, I didn't have any 20A fuses spare so I used a 15A and it seems to be holding up pretty well ....... for now. Not sure what fuse would be the "right" one.

EDIT : OH and my clock doesn't work anymore :(

[BlakTegra]

LOL
Try replacing the clock fuse

[geo41e]

the reason why ur clock doesn't werk is coz of the back up fuse is blown, which is why the prev owner ran a new wire.

under your hhood, in the fusre box, look for "back up" and shoud be a 7.5amp fuse and that fuse should be blown..theres a replacement fuse under ur steering coloumn..

another 7.5 amp fuse should be there.
HOWEVER BEFORE U CHANGE THE FUSE, MAKE SURE THE ORIGINAL BATTERAY WIRE IS EITHER CONNECTED TO UR DECK, OR TAPPED UP TO PREVENT BLOWING THE FUSE AGAIN/SHORT CIRCUTING.

[boost_morrre]

that's why u were geting 3.x V....

had a similar problem years ago when i did one in a civic and didnt know what was wrong with it.

15A is pleny for most HU's, dont put in a 20 unless u realy need to.
even go down to a 10 if u want and if that blows when u turn up your system then put back in the 15....most HU's come out stndrd wit 10A fuses....

Power = Voltage x Current

hence voltage = 12-14.4, current @ max 10A, therefore Power = 120Watts

a 4x50 watt HU is about max 30rms hence approx 120 watts at full power dissipation (proly @max volume with all adjustments set high)....normally u get a lot of distortion before this and will never get there hence the 10A fuse.