clock, courtesy lights, radio fuse blown
 

Hello, I own an unmolested '89 Coupe. A week ago, I tap the brake pedal a little hard to stop for a person. At that point my radio goes out. I say, um, blew a fuse. See that the clock has stopped and the interior courtesy lights don't work, and see the fuse #4 is blown. I replace it, and it blows as I install it. OK, I take out the original Blaupunkt radio, and the original Blaupunkt amp under the passenger seat. Try another fuse in #4 and it again blows right away. I pull out all three courtesy lights, all seem fine, no hot leads hitting grounds, the body, etc. Is it the clock? Ideas? How do you get to the clock in the car? It seems impossible for me to even see/find the lead at the back to pull it off. Any/All help is appreciated! Tom

you have a short somewhere. the clock just pulls out with your fingers. those rubber rings hold it in place with tension. you need a wiring diagram, which the host website has.

Schumicat, thanks for the reply. I'll try to pull it out today

Everybody says the host has electrical wiring diagrams....when I go there...it seems only for certain model years and ranges..... you need the factory manual and/or Bentley...and/or( horrors) Haynes. Sometimes I need all three to cross-check and balance.

I hate electrical issues, I basically suck at diagnosing them....worse than I suck at diagnosing everything else. But if I were a betting man, I'd say those systems you are having issues with are integrated and all tied together. In other words, Shumicat is probably dead-on with his analysis. You probably have a wire in there that's touching something it shouldn't. Now it's just a matter of tracking the specific wire, then finding where it's shorting out.

Firstly, I assume by your reference to "fuse #4", we're talking about FUSE #1 on the #1 Fuseblock (the middle section)....I'm working from the Bentley, BTW.

Secondly, you state that " I pull out all three courtesy lights, all seem fine, no hot leads hitting grounds, the body, etc."...what do you mean by "all is fine"? Fuse is no longer blowing? Or, you metered the hot leads on these items and found no continuity to ground? OR,...............does it still blow the fuse?

Don't forget the glove box light, as I see this in the circuit for the fuse in question...

SAME goes for the luggage compartment light...(probably the cause??)

Clarification needed...

Thanks!

Doyle

5 amp fuse, right?

Doyle

Yup, that wiring to the front compartment light is notorious for wearing through eventually. I'd say trace that wiring back behind the dash. It's possibly shorting against the body. Pull the interior lights and look for chafing wiring in the roof too.

You guys are good, that is why I love this forum. Got home from work, pulled the clock out (thanks to shumicat) tested it out of the car, and the clock is fine. Car still blowing that 5 amp fuse. Pulled all the interior lights back out, inspected the wires, started worrying about the ones in the roof, wondering how I could inspect those, when I saw that the glove box light wires head forward into the luggage compartment, and saw the luggage compartment light...forgot all about that guy....started to take it on when the wife called me for dinner. I'm betting (and hoping) you guys are right, and this is the culprit. Will find out tomorrow with my continuity tester. thank you, Tom
Yes, working right to left, first fuse in the middle 1-10 block, 5amp, really small gauge black wire feeds the devices. It has got to be that hot going to ground somewhere.

you'll find it!!!!!! drop the fuse,.....meter the hot conductors to ground.

Doyle

dshepp806 says... " Firstly, I assume by your reference to "fuse #4", we're talking about FUSE #1 on the #1 Fuseblock (the middle section)....I'm working from the Bentley, BTW..."

I hate not only Porsche electrical design and philosophy....but also their inconsistent way in which they number their fuses. The 89 will likely have a 8-unit fuseblock closest to the front of the car, followed by (touching) a 10-unit fuse block, and that is followed by (touching) a 3-unit fuse block. If we number these FROM the FRONT sequentially, I think we're talking the 18th unit. If we are counting from the back towards the front, it would be the 4th one.

Bentley, Porsche factory lit, and the various Tech/Spec books are all over the place with how they number these.

This 5A fuse feeds total interior light, glove box light, clock, and trunk light.

Bruce Anderson mentions in some of his notes that 1.) some radios were found from the factory with pinched wires as the radio chassis is slid into its receiver, 2.) the glove box light for some cars were found to be pinched and chafed, and from a lot of the guys here.... 3.) good chance that the wire that leads to the trunk area light might be chafed. I would guess there is lesser chance of there being a problem with the two dome lights, one above each door....but you never know. I'd go after the 3 most likely culprits first.

PS...don't ever be tempted to use the more easily obtained white 8A fuse in lieu of the hard-to-get-yellow 5A, maybe thinking its only 3A difference. Think instead it's a 60% increase in blow rating !!......

I specified my source (as to layout), per Bentley (which many here follow,..and is easily done). One can "deduce" from OP's circuit loads which fuse he speaks of (irrespective of source anomolies).....

We've already specified what the load circuits are/......

"Going after" the circuits means metering them......we've already NOTED that pesky trunk light ass'y as a possible (and probable) source.

So,..where are we on the actual measurements? No rehash,...Data please?

Doyle

To overfuse any circuit would provide results deserving of any poor (uninformed) soul who would commit such a gross error!!!!!!!!!!!!!!

Doyle

Has anyone even seen the yellow fuses lately?

It was, as many speculated, the luggage compartment (trunk) light. Hot black was chafed and pinched under hood hinge. Thank you everyone. Rusnak is right, the yellow 5amp fuses are rare in your walk-in parts store... never a five pack of yellows only, but if you buy an assortment pack, they give you ONE yellow fuse. I was oh so tempted to throw a white one in there today and be 'done' with it, but I just could not, and sprang for the assortment pack to get that one yellow.

I feel you, annoying they only offer one freakin 5amp fuse, Send me $1.09 and self addressed stamped envelope.

I will send you 4 at price I purchased from ACE Hardware, I bought the whole case of 22 :D They are Italian brand MTA and purple in color but are in fact 5 amps.

PM me & I will reply with my mailing address.

Draco, will send you a PM tomorrow. thank you Tom