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95 850 radio fuse #7 blown constantly, always 12V at fuse Topic is solved

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
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1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70

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95 850 radio fuse #7 blown constantly, always 12V at fuse  Topic is solved

Post by erikv11 » Sat Oct 05, 2019 6:49 pm

I managed to sort this out today before I hit "post" for help, but here is the problem and resolution:

95 850 R with factory amp at radio/heater core area and CD player in trunk.
Radio fuse (#7) blows instantly, key on or key off doesn't matter. Constant 12V across the socket according to my meter.
Removed radio and ECC unit and an't see any frayed wires at all in the radio/climate area.

What I did
- searched a bunch of old MVS threads
- found a post in this one really useful, by fazool (viewtopic.php?t=45058) explaining that power comes in from fuse #7 on two red-black wires
- after a series of "well it's not that" attempts (unhooking radio itself, CD player, etc. connectors) I figured out that unplugging the amp solved the problem. Amp is accessed from the driver's footwell.

Looks like a dead amp, not sure I will ever get to investigating that any further. Since the amp harness just plugs in between the regular harness, I could easily just switch back to un-amped setup and the radio makes noise again.
'95 854 T5-R, Motronic 4.4, 185k
'96 855 NA, 145k
'98 S70 NA, 220k (living out west)
'98 V70, T5 tune-injectors-turbo, LPT engine, 285k
'06 S60 R, 165k
'99 Camry V6 :shock: 125k
gone: '96 NA 850 210k, '98 NA V70 182k

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