Fuse holder #7 sparks

xrayspex78 · Post by **xrayspex78** » 24 Feb 2014, 12:56

First and foremost hello to everyone. I just recently purchased a 1994 850Turbo and have been correcting hack jobs left and right. One problem I'm having is with the radio or fuse holder #7. I did a voltage drop test when I took delivery of this car. The voltage starts at 0.45volts and slowly drops down to 0.03volts. Once fuse #7 is pulled it quickly drops to 0.00volts. I noticed if I leave fuse #7 in it will eventually drain my battery. I did find a bare wire in the dash behind the radio. Fixed that but it did not solve my problem. Also cleaned ground wires in front of battery, behind battery, and battery terminals. I removed the fuse box as best as I could only to find I can get so far. But I'm under the impression the spark that happens when fuse is put back in is a short somewhere. But I can't find it. Any ideas or has anyone experienced similar issues?

Post by **misha** » 24 Feb 2014, 15:23

You will need to track that wire and remove it completelly.You isolated one side of it but it appears that it's shorted somewhere else.

Post by **abscate** » 24 Feb 2014, 17:44

What voltage are you measuring that drifts from 0.45 volt to near zero?

Can you tell where you are putting each probe on this Measurement?

xrayspex78 · Post by **xrayspex78** » 25 Feb 2014, 04:58

I found the voltage by disconnecting my negative battery cable. I set my multi meter to 20 volts. I put one probe on the disconnected battery cable (negative) and the other on the positive battery cable. I then began pulling fuses until I saw the voltage drop. I've tracked it down to fuse #7 (radio/amp). I'm also wondering if the head unit itself could have a short.

Post by **abscate** » 25 Feb 2014, 05:15

I think you are measuring cosmic flux with that measurement

What you really want to measure is current (amperage ) between the disconnected negative battery cable and the negative battery post, with everything off.

WARNING!

If you leave a door open or glove box light on, and are pulling more amps than your multimeter is rated, you can burn it out. You can put a bulb in series and see how bright it glows to test for the current level without risking your meter too. A clampon style ammeter is always safe, but expensive.

50 milliamperes , or 0.050 Amps is a rough target for reasonable current drain on a Volvo.

xrayspex78 · Post by **xrayspex78** » 25 Feb 2014, 14:53

Thanks abscate. I'll try the amp test tomorrow.

Post by **abscate** » 26 Feb 2014, 05:02

I'm from the old school gauge type VOMs, btw, if you have a decent digital one it might have overload protection and be safe to use for the negative battery cable test btw

xrayspex78 · Post by **xrayspex78** » 27 Feb 2014, 18:17

Did the amp test. Disconnected negative battery cable and set multimeter to amps. Put one probe on disconnected negative battery cable and the other probe on negative battery post and got 0.00.

Post by **abscate** » 27 Feb 2014, 19:25

What amperage scale were you on? It sure looks like the drain is ok if it's 0.00!

xrayspex78 · Post by **xrayspex78** » 27 Feb 2014, 19:55

I set it to 10 amps. I also tried other settings in the amp setting and it read 0.00. But I still have a spark in fuse holder 7 when I put a fuse in. I'll be replacing the head unit with a Premium Sound head unit soon. So if it doesn't spark with a different head unit then I know the short was the original radio.