Hello. I am the owner of a 1988 Volvo 760 Turbo Wagon that has developed multiple electrical problems in relation to the tail lights, climate control, windscreen wipers and overdrive.

At the time of purchase, I became the third owner of this car in july 09. It was inspected, lisenced and insured all in the same month and the inspection shop noted no malfunctions and passed the car.

In august 09, my dad and I installed an aftermarket radio in the car. We had to remove the external amplifier that powers the volvo's stock radio system and all we did was cut the wires and not give it a second thought.

The car did not see much use from then on and sat outside throughout the winter of 2009/2010. I brought it out in the spring to give it a tune up and that was when I started noticing the problems.

1. Tail lights do not work.
All bulbs are intact, fuses are good but no power is being put out to the brake light contacts (checked with continuity tester.) I did some looking online and the problem appears to be a faulty break light switch. Any suggestions on how I test it?

2. ECC System Malfunctioning.
The dampers that control the flow of air through the different venta are not working. All I get is defrost. According to the owner's manual, the A/C light will blink repeatedly if there is a malfunction, but such is not the case. The ambient air tempurature sensors located in the front speaker grilles have a mind of their own.

4. Overdrive not working.
Ever since the new radio has been installed, the car does not shift into overdrive. The overdrive button located on the shifter does nothing and the indicator on the dash (an orange arrow) only seems to light up when the key is in the "start" position. I suspect a faulty O.D. Relay, but again I don't know where to start in terms of diagnosing it or even finding it.

5. Windscreen wipers do not shut off.
Regardless of what position I have them in, they will either operate in "low" or "high." In order to get them to turn off, I have to carefully position the switch in between the "single sweep" and "low" positions.


Any advice would be appreciated.
Lobsterbox.

 

First, there is a distinct difference between tail lights and brake lights. A bad brake light switch should not affect the tail lights. Tail lights, the lamps that come on when the parking/headlamps do, are on an entirely different circuit. So...frankly, my best advice would be to re-visit the "scene of the crime", which in this case would be the radio install. It's been a few years since I bypassed my 760's amp in favor of a new head unit. I do remember I left intact the wiring other than disconnecting the DIN cable. There was a reason I did not remove the amp but my memory is vague. I suspect, at the very least, you disconnected a common ground. While it's quite possible all the issues are not related to the stereo install, that is where I would start.
The ECC/ACC has always been an interesting bit of over engineering/under achieving. Defrost is the default position...you might try easing the temp selector towards the desired position. Let's say it's 85 degrees outside and you wish to run the a/c. Rather than setting it immediately on 70...set it to 80 and see if it works. Most likely, the ECC failure is electronic in nature; it may or may not be related to the stereo. Those ECC head units fail nowadays quite frequently and most second hand units are failed as well.

 

It's been so long since I used this forum, my apologies for not being a very active member...

Update:

Fixed all of the lights, and the windshield wiper switch, but the ignition cylinder seized in may 2011 and the car sat for a year before I got around to it again...

After bypassing the cylinder and steering lock, it fired right up, and after some brief mechanical checkups I took it out on the road... I didn't get more than a mile away with it when I smelled hot brakes so I pulled over and found that the left rear brake was disturbingly hot, and there was smoke coming from the calliper. I limped it back home, the brake seemed to have cooled itself off some by the time I got there, but I took it for a drive just recently and found that although the brake wasn't smoking hot, it was definitely hotter than the other ones... I'm going to see what I can do about spending some time taking the callipers apart, cleaning them and replacing the break pads. In the mean time, I still am dealing with the climate control and overdrive problems, although I have some new light to shed on those issues:

When I was out driving it in may 2011 shortly before the ignition cylinder seized, I noted that the climate control first of all was completely dead, no lights were showing at all. I have a hunch that it's not receiving any power, but all of the connections looked intact and in place on the back of the unit. I did more research, and eventually found a relay, called the climate control relay and I was wondering if this relay may be the source of my problems with the climate control unit not receiving power, or wether it may in fact be an internal problem in the ECC unit itself and would require replacing it all together.

The other thing I noticed on my drive is that prolonged highway use (about 15 minutes going 100km/h in 3rd gear at 3500rpm) allowed the overdrive to engage. This happened only once, as I have not had the chance to run it up to speed for that long since. My question is: In light of the above events, is the relay still the suspect given that shifting into overdrive is in fact possible, just under extremely rare circumstances, or should I suspect something else further down the line?

Any input would be appreciated.

Thanks,
lobsterbox.

 

I had this same problem on my car after I first got it 7 years ago. My wipers would come on for no apparent reason and my right headlamps would not work properly. I found out that the washer fluid pumps were shorting the electrical system out. After I disconnected the pumps in the reservoir (underneath the air box on turbo models) everything started to work like it was supposed to.