Fuse 5 keeps blowing

[todd1561]

Was driving down the road and all of a sudden the tach jumped to 6,000 and stayed there and the voltmeter and oil pressure gauges went to 0, but the car was otherwise running fine. I started to head back home and noticed the engine bogging down under load. At this time the temp gauge also went straight up. I don't think it was actually overheating, just instrumentation issues due to this electrical problem. Upon inspection I found that fuse 5 was blown (labeled dash services). As far as I can tell from the wiring diagram if fuse 5 is blown the alternator won't run. I suspect the engine bogging was because I wasn't getting enough voltage for good spark. I replaced fuse 5 and it seemed to run fine, but then the fuse blew again just idling in my driveway after a few minutes. It might be worth noting the cooling fans cycled on and off just fine once I replaced the fuse, it appears the otterstat is tied into this circuit as well. I then replaced the fuse with my ammeter and it showed about 1.5A being pulled on fuse 5. This ran for a few minutes until suddenly the 10A fuse in my meter blew. So it seems like there's some kind of intermittent short in this circuit.

Does anyone know why fuse 5 would keep blowing? I checked the connections at the fuse block and traced the green wire to where it goes into the center tunnel and don't see any obvious issues. I can keep tracing it around but figured I'd ask here before I waste too much time.

Once last thing... I did notice that even after replacing the fuse the battery light would illuminate with the ignition in the "on" position (but engine not running) as normal but was pretty dim. The brake light right underneath was much brighter. I've owned this car for almost 19 years and I can't recall if that's how it's always been, just struck me as odd. Maybe that'll give someone a clue

Thanks!

[Bitsyncmaster]

Looks like fuse 5 only powers the dash and otterstat. I've not heard of an otterstat shorting to ground but easy to pull that wire off and see if your fuse pops. If you want to run that way just jumper the two otterstat harness pins so the fan always runs. It could be the otterstat is connecting to the case which would cause a short.

If you recently had the dash out, then I would guess your flex circuit has messed up at the connector locations.

[DMC5180]

In addition to power feeds to both Instrument cluster plugs and otterstat, it also feeds the Lambda counter switch to illuminate the light. the service light should illuminate at about 30,000 miles. If you coincidentally crossed that threshold recently, it could be a factor. You?re definitely getting a dead short some where.

I this car an automatic? I believe the PRNDL light is on this circuit but not illuminated. On 5 speeds they cut the metal light socket off the wire and taped it back into the left side console harness.


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[David T]

It is possible that your "O" switch is shorted to ground. Disconnect it and watch the amp draw and see if it stays low. Make sure you don't overheat the motor during your test. You could stick a toggle switch between the two wires to turn the fans on and off during your test to get the fans to run.

[todd1561]

Thanks everyone for the input. Turns out the wiring to the otterstat fell down and was resting on the exhaust system. So it had burned through the jacket and was occasionally making contact with the exhaust which is of course grounded.

Maybe this will help someone else down the road.

[DMC5180]

Congrats, you found the ?Smoking Wire?


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[todd1561]

Haha yes indeed