96 850 Wagon -- Burnt Fuel Gage!?
 

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. :shock:

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?

:idea: 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? :D

No. I don't understand why people need remote start. I have no idea what you did wrong.

"but they can't be directly wired without going thru some coil, resistor or diode, right?"

No, they usually are wired directly to each other. I didn't look at the diagram, I admit it. Both the gauge and the sender offer resistance, and the power goes only to the gauge, so it's normal on any car that there is a direct wire connection between a gauge and its sender.

Because we [the people] are too lazy to go outside in the cold frozen weather of january at 5am to turn our cars on; and to impatient to wait for the engine to warm up.:cool:

Trust me I am no professional, but I thought that the YLW/RED connector that goes to the horn was the same that I saw under the dash. Little did I know that Swedish engineers decided to recycle wire colors multiple times.

I meant at the PCB of the Dash it self. According to the diagrams the sender unit is directly wired to the cluster, but that's all the info it gives. The cluster it self is a black box. The gage does move slightly when the car is turned on; suggesting that the coil of the gage is OK.

I believe that either I forgot to fully plug in the fuel connector at the multi-port wire box (thus not having continuity with the fuel gage) or I have a burnt resistor before the fuel gage coil.

Can anyone confirm that there is a resistor between the fuel gage coil and the YLW/RED wire and the dashboard?

Thanks Lee! (@Matthews Volvo Site)

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
http://www.matthewsvolvosite.com/for...e.php?id=19511

Closeup, Trace #1
http://www.matthewsvolvosite.com/for...e.php?id=19512

Trace #2
http://www.matthewsvolvosite.com/for...e.php?id=19513

Yes, our clusters have 1 fuse. I saw a post about a guy asking for this fuse, so....
http://www.matthewsvolvosite.com/for...e.php?id=19514

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!

You could always add a tank or freeze plug heater. Not as lazy as a remote start as you have to remember to plug it in.

http://ecx.images-amazon.com/images/...cL._SX385_.jpg

http://www.fivestarmanufacturing.com...300&height=225

Nah, I'll stick to my remote start.

On the other hand, I think I could use that tank heater for a Mercedes E300 WVO conversion.

I'm thinking of automatizing the process of heating the WVO tank with an Raspberry Pi and a Viper remote start.

Time to hit the drawing board.....................:cool: