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740 Stereo Electrical Shorting

fortbrick

fortbrick

Active member
Joined
Jan 24, 2012
Location
Indiana
Ran into a bit of a problem with my wiring recently. First, I was stupid enough to try hard wiring a non-oe power antenna without a built-in relay on it to the original connection point (which now I believe has f****d something up...) so I hunted down a little bit where it might be shorting at.

From evaluating what is going on, I have formulated what I know is working and is not.

In order for my amplifiers to get power, the antenna switch on the dash must be in the off position (top part of the switch out) ... and in the antenna connection in the trunk where the antenna should plug in I have a 30a blade fuse to complete a circuit (I found that this completes the circuit by some luck I suppose... so that allows for sound to come out of the system... kinda).

So, from what I have been thinking as of late... I believe that a fuse on the rear of the head unit is blown that controls the antenna. Often, the tiny fuse can't keep up with the stereo so the amps lose power often... but that is assumed I suppose. I now have a oe power antenna installed, just not hooked up.

Let me know what you think could be wrong, as I am no wiring expert. The stereo was installed like 4 years ago so I wouldn't remember what anything would look like unless I tore it all apart...

Just a wtf was I thinking moment. Thanks in advance if someone can be of any assistance.
 
Sadly that isn't going to be of much use. Aftermarket everything, and it was all custom wired. I just thought an idea might be had as to where the short might have gone.
 
It'll help you if you download the 740 Wiring Diagram greenbook and study the stock radio's wiring. Your aftermarlet radio needs to use same fuse/s/connections as the stock one did.

FWIW, The Volvo Wiring Diagram Greenbooks are *the simplest to read/understand* of any ever made IMHO. Once you view one, you'll see why.

Do not wire a car stereo without knowing which fuse/s and connections to make. You could cause yourself lots of problems/money/labor if you don't know anything about 12V wiring..

Thre is a TB member who has made a site making it able for you to view most all the Volvo Greenbooks, regardless of model/series/year.

Maybe someone can provide that link for him?
 
1989volvo740gl said:
Sadly that isn't going to be of much use. Aftermarket everything, and it was all custom wired. I just thought an idea might be had as to where the short might have gone.
Click to expand...


http://www.volvowiringdiagrams.com/

http://www.k-jet.org/documents/greenbooks/200-series/

http://www.k-jet.org/documents/greenbooks/700-series/

there is a very detailed 700 series STEREO INSTALLATION set
that has been posted here before..can't locate it at this moment...
will look and post back....*UPDATE* see URL below!

the 'search term' I provided SHOULD get you PAGES worth of installation
info...LOTS OF IT *aftermarket*....

googeling THIS: installing stereo in Volvo 740
gets you THIS: http://www.installdr.com/installdocs/volvo/PDF/865001.asp
 
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Sounds like you've toasted the output in the head unit. By. Poking a fuse into the antenna socket you are feeding power back into the signal line which is switching the amps on.

I've never seen a head unit with a fuse on the remote output and my head unit has a separate antenna and amp line (so the antenna comes down when it's not on radio).

Pull your fuse out of the antenna socket and put a volt meter between the remote and gnd terminals On the amp and see if you get _any_ voltage at all when you switch the head unit on and off. Shoving 12v back up the remote line into the head may well not have done it any good either. Those outputs can generally only source a couple of hundred milliamps. I've never toasted one, but then I've never tried to drive a motor directly from it either.

Can you slide the head unit out and get to the wiring at the back?
 
I pulled apart a lot of the dash, but didn't get the head unit out yet. didn't know how it locked in but i do now.

this is what we are working with:

 
You need the greeenbook to find the correct way to wire the power antenna and HU. The amp should be wired unto itself.

Do you not have the instruction book that came with your aftermarket stereo HU , speakers, and EQ products?

Are you sure you have a *short* and not a brken circuit? (were unsure if you know the difference or not)

I hear people say they have "shorts" when they just have no voltage in the circuit
 
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Haha, well, long story short... it is wired correctly already. What happened is that the original power antenna motor stopped in the up position. It never got fixed and one day a sister's friend broke it with a soccer ball. Left with a stub, I replaced it with a non-power antenna and it was one of the floppy deals. I got tired of it and wanted the original look, but I went cheap and now stuff is messed up because of it. The entire system was installed in the late 90's (when I was around 4 yrs old...) so I have no idea what is hooked up and how really besides what I can see. I got the head unit pulled and everything was hooked up right... I think it just needs all taken out and reinstalled.
 
Refer to the Greenbook for power antenna wiring.

Also, refer to www.antennasrus.com for instructions on how to replace the mast in the power antenna. This given the motor & gears are AOK.
 
So you're saying the power antenna never worked until you tried to hook up an aftermarket one?

If wiring is correct, like you say, then don't reinstall HU. It's the antenna wiring that needs correction. Aim to get antenna working with proper trigger wiring for antenna, in the process you'll probably figure out if HU is fubared...

p.s. On my wagon I disconnected the motor wiring for antenna; really annoying having it go up and down every time car on/off. I still get reception because antenna ends on top of roof. Sedan may not work with antenna end at trunk height...
 
Bensin said:
So you're saying the power antenna never worked until you tried to hook up an aftermarket one?

If wiring is correct, like you say, then don't reinstall HU. It's the antenna wiring that needs correction. Aim to get antenna working with proper trigger wiring for antenna, in the process you'll probably figure out if HU is fubared...

p.s. On my wagon I disconnected the motor wiring for antenna; really annoying having it go up and down every time car on/off. I still get reception because antenna ends on top of roof. Sedan may not work with antenna end at trunk height...
Click to expand...

no, it worked with the current HU and everything until the motor blew and then the mast broke. everything would be working right now perfectly if i hadn't tried hooking up the non-oe power antenna. it was all a-ok until i did that... this makes me think that a fuse is blown somewhere, not a wiring issue. i didn't modify the wiring AT ALL when i plugged the non-oe one in. all i did was plug the ground into the connector where the ground wire normally goes in, and then the red wire into the (positive?) part. it had black, blue, and red.

disconnected the harness from the back of the head unit and plugged it back in --- drove to work and back with the stereo on and it didn't kill itself once. maybe it's good that this is happening... it all needs cleaned and the display panel for the HU and equalizer need redone.
 
FWIW, on Volvos black isn't always ground and red isn't always + and blue isn't always ground nor positive

This is why you should consult a Volvo greenbook wiring diagram before wiring things................especially inside the car such as radios and power antennas
 
smokeyfan1000 said:
FWIW, on Volvos black isn't always ground and red isn't always + and blue isn't always ground nor positive

This is why you should consult a Volvo greenbook wiring diagram before wiring things................especially inside the car such as radios and power antennas
Click to expand...

maybe i'll learn..... one day.
 
smokeyfan1000 said:
The external ground wire for power antenna grounds to lip of "wheel house", where the two halves of the wheel house meet . This of course, is in the trunk..................


Here's a few links that might come in handy for you.......
http://antennamastsrus.com/Volvo/240/Volvo 240 Sedan 1976-1993.htm

http://antennamastsrus.com/Instructions Mast.htm

http://antennamastsrus.com/Nut Removal.htm
Click to expand...

i'm sorry, but i don't understand why you said that. i'll try to explain again. nothing with the antenna was changed from how it was before, and it is all installed correctly. the ground is on the trunk thing like you said.

from the way that the car is set up with the stereo, using multiple components, it could be anywhere. the stereo was installed at a professional stereo shop and i don't wanna figure this out myself and ultimately break something else that is now non-existant. it'll return to the original installer that installed it back in the 90's, and he will be fixing it and redesigning the center part of the dash in late july. i know it's the norm here to fix stuff yourself and use duct tape where necessary, but i just want it done right and the way it should be.

thanks for the effort in trying to help but this is a relay or a short somewhere hiding in the dash or behind my amp wall that has yet to be found.
 
replaced the voltage regulator... that cleared up the issue with the system power cycling. i'll make sure to take lots of pictures of the system when my buddy and i figure it out in a few weeks.
 
Found a short in the power antenna + wire that runs to an amp. Problem solved, and power antenna works just fine. Need a new radio cage for a '89 style 740 if someone has one...
 
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