949

car:
91 civic wagon rt.

when ever i press on the brakes or when i turn on the head lights the stereo starts to get static. its a brand new head unit. it was doing it with the last head unit as well. thats why i bought a new one.

so i need to know where are all the possible wires that can be bad or shorted so i can trace it back..

i recently repaired a some wires that a shop messed up on. they used T-taps/vampire taps and nearly severed many ignition wires trying to install some other aftermarket electical parts. looking at the wires with the taps removed, only a few strands were still connected. so i ended up repairing all of them that i could see. it helped but did not clear up all the issues. i think there are more but i need help knowing where to start looking for more issues.

plus if i start with checking the volts, what is the best technique to do it?

symptoms:
when parking or head lights or pressing on the brake pedal, the radio starts to hiss and i get static. when playing cd it doesnt do it.
i have not noticed anything that is affected.

im not having RPM hiss. its like im not getting a stereo signal or very weak signal. it sounds like im not getting a clear radio signal but i should be. i would get a clear signal if i dont put the key into the ignition position, press on the brakes, or turn on the parking lights.

recap:

i have been getting weak signal for a while and have thought it to be a bad head unit.

i just replaced it with a brand new head unit and it still has a weak signal.

symptoms and effects.

when the engine is off and the key in the ACC position, i get perfect signal and clear sounds.

when either of these are turned on i lose the signal;
key in the ON position ( the engine is off or on doesnt matter).
pressing on the brakes. (brake lights will come on).
parking light is turned on. ( no difference if head lights are on or off).


what i have done so far and nothing has changed:
i tried redoing the grounds.
i did the big three upgrade 1/0 gauge.
i replaced ignition switch with brand new OEM part.
fixed broken T-tap wires under the dash. (all the ones i could find) removed and soldered them back together.


i assume there is a short somewhere or a drain but only when i turn the key or use any of the accessories like light will the drain be more apparent.

how do i start to search for the problem?

93h2beg

read up about stereo interference. Lots of things can cause it, un shileded spark plug wires can increase it, many things on your car, poor grounds on the battery and the alternator can induce larger amounts of interference. i doubt its just a short, when u draw more voltage, ie brake lights your alternator works harder- it is probably ac leakage from an old alternator. you can check it at the lug on the alternator with it running, turn a digital multi meter to ac voltage and ground the other to the case of the alternator, if its over .2 (for 20 amp load) your alternator is junk and is causing the interference.

949

nice! i like your outside the box thinking.


i did try to do the big three upgrade. everything is 1/0 gauge. the car seems to run a bit better but the stereo static seemed to be the same.
i have regrounded and up graded anyting with ground as well. nothing has changed.

i did change the alternator a ways back, 7 years ago i think. i never did put much mileage on it though. but it could be weak i guess.

i dont want fry anything so im verifying my understanding of your procedure.
so to do you test is this what i am doing;
1. turn car on.
2. use mulitmeter on AC setting.
3. leave everything still hooked on the car and alternator.
4. touch the alternator with multimeter red lead.
5. touch the alternator case with mulitmeter case black lead.

949

another thought i have, i wonder if the oem antenna is bad?
when i push and pull the antenna in and out, the sound doesnt change at all. it doesnt make the static change. but the key is in the ACC position, which usually gives me clear sound in the first place.

the stereo's clearity does phase in and out. what i mean is that i do get get stations at a few sec bursts while either driving or wiggling the antenna cable in the back of the stereo.

to clearify what i have done so far. tests i did. i will get perfect sound when i DONT:
turn on the key to ignition position on the key (accessories position is ok),
turn on the parking or headlights,
or press on the brakes.

now playing cd or anthing else is fine.
there doesnt seem to have any draw on power. there is no dimming of interior or anything.

93h2beg

that is correct, alternators create ac voltage, they use a rectifier bridge to change to to dc . so your car can use it, when u have ac leakage the bridge in the alt. may be weak allowing more ac voltage into the system. causing all sorts of weird issues. static in stereos is one. you said you replaced the alternator, was it with a genuine honda one? or a auto parts store one? why? well auto parts store parts are rebuilt-ish if your alternator had a bad bearing when they got it, but everything else worked fine then when they rebuilt it all the company would do is replace the bad bearings since everything else checked out.

949

in the past the bolt on the alternator was not tighten down causing a tap'ing shortage which fried a few items i cant remember. so i changed out the alternator with an aftermarket unit. i have been replacing parts after parts just to recover from that shortage. hence the reason i think i still have a shortage of some sort, i just need to find all of them.

since then i have replaced a lot of parts with brand new OEM parts. with each new part i put in, it does seem to clear up little issues here and there. which im fine with. i just cant find all of them.

so with your theory, why does it still do it when the engine isnt turned over? all i neeed to do is turn the key to the ON position and the signal in the stereo is weak still?
i thought the alternator would only come into play when i turn the engine over and have it actually running.
i guess im not fully understanding the leakage.

93h2beg

i missed the engine off part i guess.

949

im thinking ill start replacing stuff. ill start with something small and cheap.
i just ordered a new antenna.

im not sure if all the 1991 civic antenna's are the same. all the sites are just showing non wagon version.

93h2beg

it is some sort of electrical interference, is your antenna hooked up to the back of the head unit securely?
is it grounded very well? I would then try to tap into the black wire coming form the head unit, and ground that directly to the dash frame.

949

i agree.

i messed with the antenna again. pushed in, out, in, out and then some more today. no difference. there is a difference if i move or touch the antenna wire under the steering column. not enough to keep it clear with the brake pressed but there is a small change. im wondering if im nudging another unkown cable under the dash as im doing this as well?

i just added another ground to the chasis of the head unit to the car. no difference. not even a little gain. arrrrgggghhh.

i tested the power this time. thinking im not getting power or some sort of loss when i press the brakes or use the parking lights. so i measured at the battery and at the stereo harness. it was the exact same at the stereo harness. 12.4 to 12.5 volts
no loss between the harness and the battery.

when i press the brakes it only drops like 0.1 to 0.2 volts max.
when i turn on the parking lights it drops the same amount. but no more that 0.2 volts. i believe these are acceptiable tolerances, but im not sure.

*tested with only the key in the ACC position and with it in the ON position. NO engine running on both key position.

93h2beg

do u have another head unit to swap out and see if it does the same thing?

DagoAcura92

A good sure way to know if you have a short is to disconnect the positive terminal on your battery and clamp a test light to it, then put the probe part on the battery post. If you have a short the test light will turn on. It basicly says that one of your positive wires is somehow touching ground.

If it doesn't turn on, you reconnect and do the same on the negative side and look for the same results.

When the light turns on you pull the fuses and put them back until the light turns off and that would be where you need to look for a short.

949

i had a clarion head unit and thought it was the problem. so last week i bought a brand new pioneer and insralled it. samething is happening.

949

ok. ill try this.

i follow u with the positive but
can u explain more why the negative too?

DagoAcura92

Sorry, late night posting, wasn't thinking right. Just the positive side.
Have you tried looking at your speaker wires? What about your antenna wire (is it the stock one that is by your windshield?), you say it only happens on am/fm, not cd. Is the antenna wire crossing paths with a computer, light switch, brake pedal, or Ignition harness?

949

no speaker wire issue. as i just added a new wire set for speakers. that didnt change the signal. i tried moving the antenna wire under the steering wheel column around. it seemed to change the static a little but its still there. i did order a new antenna from sonicelectronics. either way its an old car and old parts, so its a cheap and good replacement. i hope that will fix it before i go to the next step.

i am curious about the radio chasis. i know that there is a negative wire from the wiring harness of the stereo to the car's harness, but is the chasis of the radio also grounded some way?
because i went to a local stereo store yesterday and asked them about the static. they say its because of a weak or bad ground. im curious if i should try to ground the radio chasis as well or remove the ground from the harness and place it on another location.

davidbloom2013

It does. You have to plug in the antenna to the head unit’s antenna receptacle and then crimp the power antenna from the vehicle harness to the head unit’s wiring harness. It should improve the reception.

fcm

Say what???

That test is for parasitic drain, it has nothing to do with a short, the result would be the same if you leave anything on, [like dome light] in the car.

A short, [power lead touching ground] will result in either a blown fuse, [most likely] or burnt wiring, [not fused or improperly fused].

It also makes no diff. if you use the pos.(+) or neg.(-) of the batt. the results will be the same, it is a DC circuit.

949 Because the static is there only on radio it will be an ant. issue most likely.

It is unlikely an alt. issue as that would result in "alt. whine", a whistling/siren kind of sound, [maybe also called a hiss] that changes in pitch as RPMS change and increases in volume as system is loaded up, [things are turned on] and would be heard on radio and CD as it enters through power leads, and only if engine running.

You did say static and also when parked, [I assume you mean engine off] and that points to an ant. problem.

All 88-91 Civics use the same in A pillar ant. like this...



Now before you go and replace it there are some simple test you can do, you will need a multimeter, but before you do any testing, the pillar mount ant. all had a common problem over time, grounding...

Of the two mounting screws, one of them is for grounding the base of the ant, and two problem can occur over time, the screw and the "nut", [threaded part in car roof] will corrode, [get rusty] or the ground "strap" will break, remove the screws and carefully pull the ant. out of the pillar a few inches, so you can see the bottom of the base, make sure the "tab" of metal that is the ground strap that runs from the mast case to the screw hole is not broken, [a piece may fall out when you pull the ant. out of the pillar, so keep an eye out].

If the strap is still intact, fold it out and clean it, [both sides], clean out the hole and treads in the roof, clean the screw and remount the ant. and try the radio, hopefully if solves your problem.

If not you will need to do the tests, set meter to continuity, place one probe on ant. mast and the other to the center pin on ant. plug, you should get full continuity, if not, replace the ant., if good move probes to the outer, [larger] part of the ant. plug and the other to any chassis ground point, again you should have full continuity, if not, replace the ant.

Last test, place one probe on the center pin and one on the outer larger part of the ant. plug, there should be no continuity at all, if there is, replace the ant.

Another thing to keep in mind, the ant. must be grounded at both ends, at it's mounting base and at the radio, [outer larger part of plug], if the radio will turn on with the ant. unplugged and radio held away from any contact with the car, [other then wiring], grounding is good, either way you should be running a ground "strap" from the chassis of the HU to the cars chassis, the stock black ground lead in the stock radio harness is not really sufficient for aftermarket "high power" HUs, [that goes for the constant power lead also].

If you use a metal "L" bracket off the back of the HU to the stock rear radio support, [like the stock radio was] that will take care of grounding for the HU, also good for supporting the back of the HU so CD transport, [suspension] can work properly.

For constant power, run a fused 12ga from the batt. and connect the HUs yellow to it, don't forget to cap off the stock constant power so it can not short out. 94

fcm

What????94

949

ok. sounds good. ill try the procedure.
i did order the new antenna and it has arrived. i have yet to try to install it. there is no instructions on how to install it properly. i know it looks simple but if there are small parts that needs to be done a certain way i wouldnt know.

looking at the package there is a ground strap on it. how is that attached?

fcm

If you already have the new one, install it.

The easiest way to install a new ant. is to pull the old one out a few inches, cut the ant. lead, remove the mast housing leaving the old lead in place, attach the new ant lead plug to the end of the old lead, [I shove the center pin of the plug into the old lead and tape, [electrical tape] them together so they do not pull apart, tape the new ant. lead to the bottom of the new mast housing, [one wrap of tape] so they cannot separate easily.

Now slowly pull the old lead, [down in the kick panel] untill you can feed the base of the new mast housing into the "A" pillar, then pull the old lead and feed the new ant. into the pillar, be carefull so as not to pull the old lead from the new lead, do not force it if it gets stuck, pull it back out a little and try again twisting the new ant. a little to get past the obstruction.

Once you get to the point where you taped the lead to the mast housing you will have to separate them, [reason for only a single wrap] continue pulling the lead as you push the rest of the ant. into the "A" pillar, install mounting screws.

One of the screws goes through the ant. base and through the "ground strap" to ground the base of the ant., don't forget to clean out the screw holes in the roof once you get the old mast out.

With all that said, I would still do the checks first, there is no point in throwing out a perfectly good ant. just because all that was wrong was a bad ground. 94

949

i just tested the continuity part of it. i wont have time to replace it yet.

the two bolts to each other. have con't.
bolt to mast. no con't.
mast to body. no con't.

i didnt have time to take the radio out and do a deeper test yet on the other ends.

949

update:
im not really sure what i did to fix it because i did a combination of things.
so currrently it is working much better.

i replaced the mast with a brand new one.
i got new bolts that attach the top of the mast to the roof.
i regrounded the stereo chasis.
moved around the rear antenna wire.