1990 740GL, electrical strangeness

  • Thread starter Thread starter JayR
  • Start date Start date
J

JayR

After driving to a fish pond on a rough, bumpy dirt road, my 1990 740
started doing some strange things.

When I turned on the headlights, the wipers come on. I had to pull the
horn/wiper fuse to get home without the wipers screeching on the dry
windshield.

The next day, I noticed that the power windows were dead, but the fuse
looks good (I don't have a 30A handy to actually switch it out and test it).

Next, the turn signals went out, and the fuse is blown. However, when I
put in a new fuse, it blows immediately.

Obviously, something electical is wrong. A short somewhere perhaps?
How is something like this diagnosed by the home mechanic?

Thanks,
Jay R.
 
JayR said:
After driving to a fish pond on a rough, bumpy dirt road, my 1990 740
started doing some strange things.
Click to expand...

On the inside of each wing (on my UK spec 740, at least) is a bunch of earth
(ground) terminals. I'd start by checking all of them as 740s seem to have
real problems with earthing. Check the engine earth strap too (attached to
the bulkhead). It seems that it was made a little too short - mine had
snapped.

Si
 
Mungo said:
On the inside of each wing (on my UK spec 740, at least) is a bunch of earth
(ground) terminals. I'd start by checking all of them as 740s seem to have
real problems with earthing. Check the engine earth strap too (attached to
the bulkhead). It seems that it was made a little too short - mine had
snapped.
Click to expand...

Sounds good, I'll check. Er, what's the USA word for what is called a
"wing" in the UK?
 
Fender. Boot is Trunk, Bonnet is Hood, estate is wagon, saloon is sedan,
Sills are Rocker Panels, manifolds are headers. I may be wrong about Fender,
but it is the word that sprang to mind.

All the best, Peter.

700/900/90 Register Keeper,
Volvo Owners Club (UK).
 
I have just gone through the same deal with my 90 wagon.
After going to all the forums I could and getting the ground is bad
answer. I finally tore into it with a vengeance.
If this hasn't been repaired yet you will need to take out the glove
box and the kick panel on the passengers side.
You will find a cluster of red wires all hooked into a buss bar by
spade connectors.
this will be covered by a plastic cover which may show signs of melting
from the heat generated by a poor connection. Hey Volvo fire the bum
who came up with this little fire starter!!
Once you find it their are 2 ways of fixing it .
You can cut off all the spade connectors and twist and solder , wire
nut and electrical tape the whole wad, or you may chose to solder the
spades onto the buss bar as I did.
Either way that took care of most of my electrical spooks.
You can do it now or you can do it later but you Will be doing it
sometime as this set up causes a lot of grief to Volvo owners. Mine
caused the car to quit while in traffic and wouldn't start until days
later at my garage when this mess was found.
And oh ya I checked all the ground stuff twice!!
Good Luck
Mac
 
Mac,

This sounds great, I will definitely make this a project.

Regarding my 740, I checked the grounding harnesses inside each fender.
There were two on the passenger side, and one on the driver's side.
They did not look corroded and were properly affixed. I didn't see any
wires that appeared to have come unclipped from either fender ground.

I did find one more clue to my problem. I noticed that my driver's side
headlight is extremely dim. When I turn on the left turn signal, both
the driver's side headlight and the flasher blink weakly. The passenger
side light is fine.

So right now the turn signals are working again (new fuse that didn't
blow immediately this time) and the power windows have resumed working,
mysteriously. However, I still have the dim headlight and the wipers
still come on when I turn on my headlights. So something's still not
right and I need to get it fixed, but I am driving the car.

JayR.
 
JayR said:
Mac,

This sounds great, I will definitely make this a project.

Regarding my 740, I checked the grounding harnesses inside each fender.
There were two on the passenger side, and one on the driver's side.
They did not look corroded and were properly affixed. I didn't see any
wires that appeared to have come unclipped from either fender ground.

I did find one more clue to my problem. I noticed that my driver's side
headlight is extremely dim. When I turn on the left turn signal, both
the driver's side headlight and the flasher blink weakly. The passenger
side light is fine.

So right now the turn signals are working again (new fuse that didn't
blow immediately this time) and the power windows have resumed working,
mysteriously. However, I still have the dim headlight and the wipers
still come on when I turn on my headlights. So something's still not
right and I need to get it fixed, but I am driving the car.

JayR.
Click to expand...

Whenever you have dim lights, and switches from one device affecting
another, then I always suspect grounds. Keep in mind the problem can be
anywhere on the ground wire from the connection at the device to the
connection on the body.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)
 
Mike said:
Whenever you have dim lights, and switches from one device affecting
another, then I always suspect grounds. Keep in mind the problem can be
anywhere on the ground wire from the connection at the device to the
connection on the body.
Click to expand...

Ok, then it's pretty certain I've got a grounding issue. If I've
already looked in the obvious places and don't see bad connection, is
there a way to locate a bad ground, like a tool of some kind?

JR
 
JayR said:
Ok, then it's pretty certain I've got a grounding issue. If I've
already looked in the obvious places and don't see bad connection, is
there a way to locate a bad ground, like a tool of some kind?

JR
Click to expand...

One tool that is necessary would be a voltmeter. Put one lead on the
negative battery terminal. Measure the voltage at the ground wire at
the headlight. It should be close to zero, I'd say maximum about 0.3
V. Another tool that would be very helpful is a wiring diagrams manual,
so you know which colour wires are supposed to do what.
Because your wipers are turning on, I ask the question, what are your
windshield washers doing during all this?

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)
 
Mike said:
Because your wipers are turning on, I ask the question, what are your
windshield washers doing during all this?
Click to expand...

Washers are inactive -- it seems to be affecting only the wiper motor.
 
JayR said:
Washers are inactive -- it seems to be affecting only the wiper motor.
Click to expand...

What turns the wipers on other than the wiper switch? The washer pump.
Energizing the washer pump fires up the wiper motor, so if your
headlight is being grounded through the washer pump, then the wiper
relay will be receiving a signal down that wire, and will turn the
wipers on. Try disconnecting the wires at the washer pump.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)
 
Mike said:
JayR wrote:
Click to expand...
Rather than just rely on my visual inspection, I decided to follow the
advice here and disconnect/clean/reconnect the ground wires inside the
fenders. Vallah! Problem gone.

I still don't really understand why my #8 fuse (turn signals) was
blowing immediatly upon insertion, but everything's back to normal now.

Thanks to all who responded!
 
mudguard fender wing bulk head fire wall boot trunk bonnet hood
gear stick gear lever auto car gas petrol
 
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