head unit wiring problem

[dbun]

hi guys,

i have a 3rd gen prelude and I am trying to wire in a headunit. The problem i've found is that the constant battery on wire is only putting out about 9-10 volts when it should be around 12 volts, therefore the headunit does not switch on. However if i wire the accessories and power from the headunit to the accessories wire in the prelude it all works fine, but this is dodgey. Any ideas about the low voltage output on the constant battery on wire??

[ICACHA]

did your original head unit work fine?

you might have a dodgy fuse in the fuse holder of the car, get that checked out :)

constant should be white with red stripe, or another colour stripe, you sure you know what your doing? :p

[ICACHA]

radio reception will also be weak if you didnt connect the antenna trigger either, thats another thing that isnt easy to work out :) some secrets do need to be kept on how we test for antenna triggers :p

[dbun]

yeh old h/u worked fine.

Basically because i didn't have the wiring diagram for the prelude i pulled out the old h/u and with masking tape noted what wire was what by looking at the h/u manual.

Then when i had twisted all the wires together and was about to solder and heatshrink the connections i quickly tested the h/u and it didn't switch on......so then i got the multimeter out and found the power wire to be 9.8 volts when i thought it should be about 12v.

I do electrical engineering so i'm not a complete idiot when it comes to wiring gear up....i'm just new to the auto electric side of things if that makes sense.....not 100% sure on how much voltage is supposed to be where etc. I mean from my understanding when the car is of.....there should only be one wire that is putting out voltage??

[destrukshn]

yes check fuses first or just trial replace.

[dbun]

yeh i pulled the radio fuse and had a look at it......looked intact to me.

Maybe i'll just try swapping it with one of the spares in the fuse box.

[zorrt]

constant should be the readout of ur battery. have you checked the reading of your battery?

[dfekm3]

if all else fails, just run a new wire for the constant wire to the head unit and ensure that that wire has 12V to it constantly

[CRXer]

Hello mr elec engineer.Funny how things look different when you finally get your hands on the wires! whats the diff between a car,a computer & a fully automated factory? nothing,they are all just things with wires connecting a hole lot of different forms of switches to somethin else(sorry,sparky here who has had too many hassles with the theory boys)
Im assuming your wiring into the stock harness plug?
There are lots of things that are pre-ignition under the dash,including your lights.A loss of voltage would tell u that its dropping across something wouldnt it?Im also assuming its not a bad joint(cos u got the heat shrink out & everythin),so it sounds like you picked up the dash light wire.Turn your dimmer up and down & see if the volts change more.Usually a red/black wire in hondas ive worked on.What you want is (i think again) a white/yellow wire or if your running a super high power h/u a fused wire back to the pre-accessories white/black wire.There will be enough power here unless u go adding amps off the same supply,but i dont have to tell u the theory,do i?
Btw

some secrets do need to be kept on how we test for antenna triggers
.....secret?......................tracing a wire that activates somethin?? ........................was this part of the Q???...................
You gotta find some new secrets man...........

Sorry guys,feeling obnoxious,had a few :p

[ICACHA]

yeah its white/red or white/yellow or white blue, same thing i just mentioned in another post as wire colours change, locations dont :)

CRXer, funny how people who specialise in one field are hopeless in another :cool:

i say, check, double check and triple check :wave:

well its not much of a secret for those in the know, but for those who DIY its a secret to find the trigger wire as i wont tell :p

[Slow96GSR]

You keep trigger testing a secret? Shit guys I'm sorry to say but you are all bad at keeping secrets, everyone I know knows how to find it, and I didn't tell them!! LOL!! That's ok, anyone with half a brain should be able to figure it out, I would hope.

Check your connections like ICACHA says and make sure the battery is charged and the connections on the battery are good. If it reads 12v on the switched input, then it should read the same on the constant… maybe +/-.01-.02 volts but that’s a big maybe, haven’t seen that happen much and only when a connection is bad. Use a Multimeter to check all the wires and don’t hook up the new head unit until you are sure all the connections are correct. Nothing is worse then having it all set right and hooking up a new head unit and finding out you blew it when a wire was crossed.