only 4.2 volts!!!!
Discussion
ok so i tried to wire in a new stereo today...........nice easy job!!
wired in an ISO connector with live feed 12v from ignition, permanent 12v for memory, earth and 4 speakers, all fairly simple so far but it all goes wrong when i plug into back of head unit, the 12v feed from ignition drops to 4.2volts but when disconnected i've got 13.8 (with engine running). so now i'm confused how can it suddenly drop when i plug it in???
i must warn you that i'm no electrical genius so please feel free to state the obvious and assume i'm an idiot!! i did notice before when i was checking electrical circuits on the fuse and relay panel that if i tried to use a metal part of the car (hinge, bolt, etc) that i could only get around 4 volts and had to run a wire direct from the battery neg to get a good 12v reading!
wired in an ISO connector with live feed 12v from ignition, permanent 12v for memory, earth and 4 speakers, all fairly simple so far but it all goes wrong when i plug into back of head unit, the 12v feed from ignition drops to 4.2volts but when disconnected i've got 13.8 (with engine running). so now i'm confused how can it suddenly drop when i plug it in???
i must warn you that i'm no electrical genius so please feel free to state the obvious and assume i'm an idiot!! i did notice before when i was checking electrical circuits on the fuse and relay panel that if i tried to use a metal part of the car (hinge, bolt, etc) that i could only get around 4 volts and had to run a wire direct from the battery neg to get a good 12v reading!
Hi Al
I assume your asking because the stereo fails to work
The usual reason for "dropping" voltage is poor connections. I assume as you have poor earthing via the metalwork on the car that you've run an earth directly from the negative terminal of the battery? obviously check the soundness of any joints or connections in the wiring you've done , check that the connections on the 2 halves of the iso connector marry up and make a sound connection too. do you still get 12v between the permanent live and earth when connected up ? Is the stereo unit a proven working unit?
As with all things check the simple stuff first before assuming its something major.
Good Luck
Ron
I assume your asking because the stereo fails to work
The usual reason for "dropping" voltage is poor connections. I assume as you have poor earthing via the metalwork on the car that you've run an earth directly from the negative terminal of the battery? obviously check the soundness of any joints or connections in the wiring you've done , check that the connections on the 2 halves of the iso connector marry up and make a sound connection too. do you still get 12v between the permanent live and earth when connected up ? Is the stereo unit a proven working unit?
As with all things check the simple stuff first before assuming its something major.
Good Luck
Ron
stereo is brand new so should be good
yes the permanent live is ok and will hold 12v plugged in or out
so its likely that the ignition feed has a poor connection somewhere!!
is the bad earth on the car something to worry about? i've used new earths where ever possible and cleaned where it connects to chassis, is there a main earth from the fuse box?
yes the permanent live is ok and will hold 12v plugged in or out
so its likely that the ignition feed has a poor connection somewhere!!
is the bad earth on the car something to worry about? i've used new earths where ever possible and cleaned where it connects to chassis, is there a main earth from the fuse box?
HI Al
as a quick check disconnect the live feed from the ignition and then use the permanent live to feed both the live terminals in the iso connector. Everything should now work ok (other than the fact that the stereo wont turn off with the ignition) .This will prove all the other wiring & stereo unit is ok just leaving you to investigate why there is an issue with the live feed from the ignition.
Ron
as a quick check disconnect the live feed from the ignition and then use the permanent live to feed both the live terminals in the iso connector. Everything should now work ok (other than the fact that the stereo wont turn off with the ignition) .This will prove all the other wiring & stereo unit is ok just leaving you to investigate why there is an issue with the live feed from the ignition.
Ron
Yet another chapter in dodgy wedge wiring !!
Try testing with your test meter straight from the -ve battery terminal (use a long piece of wire if necessary) then see if the +ve voltage drops at the stereo when switched on. If it does, you have a faulty connection in the LIVE feed (or fuses) somewhere.
Then test the earth from the stereo (still connected to battery -ve terminal). If you get any voltage reading at all (i.e. more then a few millivolts) when stereo turned on, then there's a faulty connection in the earth feed.
(with luck the voltage readings will add up to 12 !)
In my humble opinion, always supect a dodgy earth return first on the wedges, checking carefully for corrosion. As most of them have ordinary nuts and bolts around the place used for wiring, it's not surprising. THEN check the fuses for corrosion too.
You can always check for voltage drop along wires when relevant thing is switch on.
(from +ve or -ve battery terminal) and it should never be more than a few millivolts.
[There is always a small drop, as every wire has some small resistance]
Hope this helps !!
Try testing with your test meter straight from the -ve battery terminal (use a long piece of wire if necessary) then see if the +ve voltage drops at the stereo when switched on. If it does, you have a faulty connection in the LIVE feed (or fuses) somewhere.
Then test the earth from the stereo (still connected to battery -ve terminal). If you get any voltage reading at all (i.e. more then a few millivolts) when stereo turned on, then there's a faulty connection in the earth feed.
(with luck the voltage readings will add up to 12 !)
In my humble opinion, always supect a dodgy earth return first on the wedges, checking carefully for corrosion. As most of them have ordinary nuts and bolts around the place used for wiring, it's not surprising. THEN check the fuses for corrosion too.
You can always check for voltage drop along wires when relevant thing is switch on.
(from +ve or -ve battery terminal) and it should never be more than a few millivolts.
[There is always a small drop, as every wire has some small resistance]
Hope this helps !!
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