96 850 Wagon Burnt Fuel Gage?

[jose456891]

Before you do a face palm let me be the first to admit to committing a major crime against humanity:

I started poking wires with full battery voltage in hopes of finding which of the trillion YLW/RED wires hook up to the alarm horn.

And in the process I screwed up the fuel gage.

Why? because I wanted to hook up my remote start to the alarm horn instead of the main horn (main horn requires a DPDT isolation relay and more wires for integration)

So far I tested the sender unit and it's resistance is within spec. The yellow/red wire that goes from the sender unit to the dashboard has infinite resistance, indicating an open circuit. This is the same wire that connects directly to the dashboard to display fuel level.

The wiring diagrams do not show any over-current protection between the sender unit and fuel gage, but they can't be directly wired without going thru some coil, resistor or diode, right?

Here is what I think happened: I managed to fry a resistor between the sender unit and the fuel gage.

Can anyone chime on this before I start taking the entire dashboard apart?

[Ozark Lee]

Download the schematics (I can't post anything from them anymore without getting the Volvo lawyers all riled up) and locate the junction points between the sender and the dash. I haven't looked at the schematics but you might be able to isolate the problem between two junction points. and cut down on the areas that need to be investigated.

I know of no resistors in the line between the sender and the instrument cluster, just wires.

The schematics can be downloaded from here:

http://www.volvowiringdiagrams.com/?dir=

Download a couple of years, there aren't any differences in that circuit but some of the schematics are incomplete.

...Lee

[jose456891]

Thanks!

[jose456891]

Thanks Lee!

I found the culprit. I was tracing the continuity inside the dash from pin 3 to ground. I noticed that the cluster fuse (yes the cluster has a built-in 5A fuse), resistors, diodes and capacitors all had their original and correct specs. But... somehow the continuity was interrupted before it reached the cluster's microprocessor.

It turns out that Swedish engineers have outdone themselves again! The thin copper traces from pin 3 (sender unit YLW/RED signal) broke just before the MP!!!

Seriously, I would be buying a new/used cluster if these tiny copper traces had not burned up.

Anyhow, take a look at the damage, a tiny amount of solder + hair thin copper will fix it!

These electronics (w/ expection of ABS & IGN) are just built to last!

Trace #1

Trace#1

Closeup, Trace #1

Closeup

Trace #2

Trace#2

Yes, our clusters have 1 fuse. I saw a post about a guy asking for this fuse, so....

Fuse

I learned my lesson, either do things the right way, by using a wire traces & a DVM rather than touching every lookalike wire with battery voltage, or the highway!