Underdash Electrical Fire

[danl]

Driving along today I was shocked to see smoke coming from under the dash (left side). It stopped quite quickly (thank God) and upon inspection the headlights don't work. Obviously, it was headlight wires under the dash shorting out on something.

Strangely, no fuses were busted. I'm not familiar with relays (yet) but I've read that they are the way to go with high draw lights. I ordered an H4 upgrade today from our hosts and plan on installing a relay.

So, before I dive in (and under) any words of wisdom/caution?

I'm sure I'll find some fried insulation - I was wondering if there is a typical place where I'll find the cause (headlight switch, stalk hi-beam switch etc) or if there are some tips for making the situation a little safer.

Any help is appreciated.

Oh yeah, Bone stock 78 SC with sugar scoops....

[rgrimm]

No expert, but I think you've narrowed it down pretty well.

Make sure you look carefully at the wires for melted insulation. I have a short under the dash and chose to have my wrench look at it--he cut back into the harness, replacing any wires that looked suspect.

I assumed that a replacement dash harness would be typical outrageous Porsche prices. But I might add that when I checked with the dealership's parts department, they even looked at the price twice. If I recall, an entire replacement dash harness was only $40-$50, so that may be a good option, at least for peace of mind.

[project 911]

This is a bit tough to read, but it might help.

[danl]

Ah, thank you...

That last article somewhat explains why a fuse didn't blow and is related to the circuit (headlights and dash lights) that I'm experiencing problems with.

It'll be a rats nest under there, but there's no way I'll stop until I figure out a solution.

If a dash wiring harness is that cheap I'll certainly look into it. I can only stand so much heat shrink and red wires before I replace the works.

[sporqster]

I'd appreciate a link to that ~$50 dash harness if someone's got one. I've got a '79 in the garage with a rat's nest of suspect wires... (and wipers that occasionally 'automatically' activate)

[fintstone]

There are 3 or 4 known dangerously unfused circuits like this. There was a thread on it a while back where they...and their fixes were discussed. This one, one was with the early SC footwell blowers another had to do with the front A/C condensor fan.

[RoninLB]

Trunk light sw and glove box sw fails and it should be on the dash light circuit. I installed a 4amp mini resetable circuit breaker from a marine supply store. That circuit is a fire waiting to happen imo.

[GeorgeK]

Start with that:
Dash lighting fuse installation

Then, do a search for headlight relay install. These 2 items should cover you for the future.

[Wil Ferch]

Yeah...its' likely the terminal number is 58a....not 58L as mentioned in Steve Grosekemper's article....

...had me scratching my head for a while.....

- Wil

[danl]

Originally posted by Wil Ferch
...had me scratching my head for a while.....
- Wil

Ah, Wil Ferch.... we meet at last.

You'll be happy to know I am about to apply the "Ferch" method to my suspension mods...

Cheers!

Oh yes,

UNFUSED CURCUITS? That's just plain crazy. Will fix.

[Wil Ferch]

danl:

let us know how it goes...people who use the system to set up ride heights seem to say the method works.....

- Wil

[madmmac]

What years are affected by the dash fire hazard?

[edward993]

Hmmm, very interesting stuff. Crazy to think that Porsche would have unfused circuits, let alone a high-draw one. Can anyone post all the unfused circuits? I'd like to address these as a preventative measure, and nailing them all at once would be great. Thanks!

Edward

[danl]

Originally posted by edward993
I'd like to address these as a preventative measure, and nailing them all at once would be great. Thanks!
Edward

Yes, this would be useful. I'm into my second year of ownership and there are many things I just don't come across unless a disaster befalls. For example, I was planning an H4 upgrade and I knew that using relays was in the cards but I didn't know that constant use of my hi beams would fry my wiring. I read tons of threads but this never came up in my reading even though it has been discussed several times.

Now, it looks like my stalk switch is toast and there are a few wiring upgrades (inline fuses) that I'll be installing. I would have loved to have known about these little items ahead of time.

It seems like a good section for the next edition of 101 projects. An Electrical Fire Prevention and a Fuel Leak Prevention would be great especially for the new-to-you Porsche owners.

[Wil Ferch]

Better sit down....I 've posted this before...
- Wil
===============================

There are many more electrical areas..Porsche does a really poor job in this category.
- For A/c cars....add the 7.5A fuse kit for the front condenser fan. Another fire hazard.
- add headlight relays, as mentioned
- add upgraded relay with external 16A fuse in smugglers box ( A/c system)...late 70's to late 80's cars.
- oddly *all* relays that Porsche uses ( ex: foglight relay) is fused only on the power side...not on the control side. Quick wire switcheroo will fix this.
- fuse box disaster. Design uses riveted construction of fuse holders that may get loose over the years. At some point in time, take box out, re-tighten or solder the rivet connections. Some of these have "bus-bar" connections that jumper incoming points on the fusebox. Or use external wire jumpers. Best to add external wire jumpers *everywhere* there is a bus connection with no external jumper wire to begin with. This would end up being a duplicate, parallel circuit.
- 930 A/c system gangs too many loads into too few circuits. Steve Grosskemper ( again) ....or was it John Rice..offers suggestions on how to add more fuses to separate these loads and have the wires run cooler. I think this article resides somewhere in the Pelican Tech Article section.
- no headlight relays ( as mentioned)
- other interior lights are still not fused with this mod ( cig lighter...fresh air panel).

I could go on....but I'm getting ill again thinking about all this...and all the work ahead of me to remedy these "excellence expected but not achieved" designs. What did Porsche do?..hire apprentice electrical designers??


- Wil Ferch

[Cipotifoso]

"Removing the Headlight Switch" - Isn't that a project in itself?
Also, Wil, when you say "Quick wire switcheroo," what exactly do you mean (forgive my ignorance).

Thanks!

[danl]

Originally posted by Wil Ferch
Better sit down....I 've posted this before...
- Wil

Yeah, my searches are turning up all sorts of stuff. Unfortunately, "Electrical Disaster" was not in Wayne's Book, nor in the Bentley Manual, nor in the many buyer's guides that I read.

Tensioners, Air Box, and Rubber Centered clutch are listed as the "problem areas" of my era of 911. The 2nd and 3rd items seem like a walk in the park compared to a fiery death.

Again, thanks. Heavy Sigh.

[Bobboloo]

Originally posted by danl
So, before I dive in (and under) any words of wisdom/caution?

This has already been mentioned in the Steve Grosekemper post but I'll reiterate it. Disconnect the battery before you do any work on the electrical. Not only are a lot of these circuits unfused but they are also unswitched. They are always live whether the ignition is on or off.

[Wil Ferch]

In some cases...like when the control circuit of a relayed device is not fused ( say...the wire is on the "top" of the fuse board...the "incoming" line)...a simple "switcheroo" like moving that particualr wire to the bottom ( output side) of the fuse board on some proper....nearby...fuse....

...can sometimes work...

- Wil

[Gene Wilkes]

I just went thru this with my 911. The PO didn't add in the relays and the result was a melt-down at the headlites and a melt-down at the switch. Don't remove the old switch until you get the new one and replace one wire at a time to make sure you get them all back in the correct slots. Digital photos of stuff helps you to remember too! I used this company to get a heavy duty wiring relay setup and am happy with it! http://www.eautoworks.com/html/ORD-1-1-1-23754.cfm