1996 850 Battery Drain Overnight - Yellow Wire Problem

[PeteB]

Our 850 has had a problem with the battery dying overnight for a long time.
I debugged this by removing the bolt and wire lugs from the post at the battery.

Then measured zero amps to the big starter wire and the single smaller red wire.

The larger lug with a bundle of red wires and a single yellow wire had the high draw.

Measured the bundle with an amp clamp and the high draw was the yellow wire.

I can follow the yellow wire about one foot then it goes into a big harness no idea
where it goes.

I found what I think are 1995 wiring diagrams but could not find any yellow wire going to the battery.
Anyone know what the mystery yellow wire is?
Anyone have an accurate wiring diagram for the 1996 850?

Here is another person having the same problem who found he could snip the yellow
wire and the car works fine but obviously it has to be something, I'd worry if it was the air
bags for example, this is their picture but ours looks the same:
He snipped all the wires and crimped on several new lugs leaving the yellow wire out.
Picture is from: https://volvoforums.com/forum/volvo-850 ... nal-84878/

VOLVO-850-YELLOW-WIRE.jpg (137.04 KiB) Viewed 1582 times

[abscate]

Pete..you’ve picked up one weakness with current track type wiring diagrams like Volvo provides. Only the wiring appropriate for the subsection are shown

I don’t see the yellow wire in the power distribution section, but it could be somewhere else, and unfortunately there is no way to see where to look.

If there is a #/## convention on the battery, maybe search that?

[BEJinFbk]

I have a sneaking suspicion that the yellow wire may not be stock.
Does this car have an aftermarket stereo, or any sign that it used to?

[PeteB]

That picture is off the internet and they are having the same problem that we are.
There is one very large factory terminal lug that the yellow wire goes into, it is
original, it even goes into a factory wiring harness.

I might just stop into the local Volvo dealer and ask in the parts or service dept.

And to answer your question, no this car does not have an aftermarket stereo, alarm
or anything else as far as I know.

[jreed]

For what it's worth, my '97 855 GLT also has the same yellow wire going to the positive battery terminal.

[RickHaleParker]

The yellow wire goes to the Secondary Air System. It supplies the power for the Secondary Air Relay and the Secondary Air pump.

In the wiring diagrams you will find the yellow wire in the Engine Management and Sequential Fuel injection sections for Fenix 5.2. & Motronic 4.4.

On the Motronic 4.3 the yellow wire goes to the Ignition switch.

The electrical wiring diagram for the 1996 850 is Volvo TP3911202.

2/53 Secondary Air Relay
6/54 Secondary Air Pump.

[abscate]

Do instead of cutting the wire , pull relay 2/53 and test to see if it is fused closed.

If it isn’t , your ECU is pulling the relay closed by fault.

You can solve the drain problem by just pulling the relay.

[PeteB]

Thanks very much for finding it and posting those diagrams.

I pulled all the relays in the fuse box some time ago, do you know where relay 2/53 is
located? I seem to remember a relay down near the SAS pump is that it? I don't have
the car here it is with my son.

[RickHaleParker]

2/53 is somewhere around the driver's side headlight. It is probably under the battery tray where the SAS pump is.

1. Remove Air cleaner.
2. Remove battery.
3. Remove battery tray.

[jreed]

The SAS relay (at least on my '97) is clipped to the the air pump bracket. It's easiest to get to from under the car. I had to replace this relay after it failed closed on my car about 10 years ago. The symptom was the air pump stayed running, even when the car was shut off. I replaced it with a "KAE" brand relay, which worked well.

The relay is shown in this picture:
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