1979 Underdash Electrical Question

rjm65 · 11:22 AM

Just starting to sort out some of the wiring bugs on my "new" 79 and thought I'd start off with a few questions.

1. Under the dash there appear to be two rheostat controls, one on the left side and one on the right (little wheel with serrated edges). I believe one controls the brightness of the dash lights (right side?), what does the other one do? Dash lights are extremely dim, adjusting the rheostats makes no difference.

2. Engine off, key out, moving the turn signal control to either left or right will make the corresponding light come on (but not flash). It appears like the PO tapped into the hazard switch to grab power for the radio (I'm going to rewire that), so not sure if that might have something to do with it.

3. Attached is a picture of a loose connector I found just hanging under the dash. Not sure where it should go or to what.

4. Is there a cover panel that goes underneath the steering column?

That's enough for now!

Thanks,
Raymond

Danglerb · 02-25-2008, 11:53 AM

Dash light dimmer often gets dirty or worn out contacts, you may be able to clean it.

Kinda looks like speaker wire on the back of that knob, maybe something installed by a previous owner?

rjm65 · 02-25-2008, 01:25 PM

If you look at A on the photo, just want to confirm, is that the dash light dimmer? If so, I have another one just like it towards the left side of the dash. What's that one for?

B isn't actually a knob, the end is threaded and there are electrical contacts inside the socket.

Is there a switch inside the car to turn on the interior lights?

Danglerb · 02-25-2008, 02:39 PM

Let me change my answer to not sure on the first part. Could be a test connection, maybe only used at the factory. Dash light dimmer and wiper interval are the only things I can think of, but just guessing.

Lights work off the pin switches in the door frame and at least I think the light above the windshield mirror has a 3 position switch, off, on, depends on door open or closed. Interior lights may have a fuse etc. out since they are the number one battery drainer when they go bad.

Landseer · 02-25-2008, 04:35 PM

The turn signal light is behaving as-designed. It allows the car to be parked on the shoulder of the road, marked by low-voltage signal lights on only the pertinent side of the vehicle, ie, the side hanging out in the road. Kind of a parking light situation that minimizes current draw but serves the purpose of lessening chances that another motorist or bicyclist will crash into the car.

Landseer · 02-25-2008, 04:37 PM

Hanging fixture --- isn't it a bulb-holder for a map light that fits in the missing cover beneath the wheel?

rjm65 · 02-25-2008, 05:48 PM

Quote:

Originally Posted by Landseer

The turn signal light is behaving as-designed. It allows the car to be parked on the shoulder of the road, marked by low-voltage signal lights on only the pertinent side of the vehicle, ie, the side hanging out in the road.

Good thing I didn't fix it!

Makes sense on the loose connector being for a bulb.

But one thing I still haven't figured out is how do you turn on the interior lights? I haven't found a switch for it (this is my first Porsche so I'm kind of finding my way around).

Danglerb · 02-25-2008, 06:40 PM

Switch is on the lights, above the mirror in the front, on each door, and back on the rear hatch.

Incognito · 02-25-2008, 08:34 PM

I believe the left is dash lights and the right is wiper delay.

rjm65 · 02-25-2008, 10:03 PM

Confirmed the left one controls the lights.

The light above the mirror has no switch on it. I know there's a pin switch on each door and on the hatch, but can't find a manual on/off switch.

Alan in AZ · 02-25-2008, 11:23 PM

There is a switch - rock the whole lens front to back: middle is off, one way is permanant on the other way is door switched mode.

There is no single overide for on or off - each fitting has its own switch.

Alan

Alan in AZ · 02-25-2008, 11:24 PM

Quote:

Originally Posted by Landseer

Hanging fixture --- isn't it a bulb-holder for a map light that fits in the missing cover beneath the wheel?

No

rjm65 · 02-26-2008, 11:10 AM

My lights can't move back/forth. Car is a 79, so maybe they changed this on later years. I'll post a picture of the inside lights later.

rjm65 · 02-26-2008, 02:54 PM

Here's a picture of the inside light, it can't move back/forth.

Also, I've checked my instrument light dimmer switch with an ohm meter, the switch is fine. I also have the lead that comes off of the dimmer switch (on the light bulb side of the circuit) and when I apply +12v the lights pop on. What I can't find is the actual +12v lead that connects to the dimmer switch. I see no unused connections behind the dash.

Where does the +12v lead that connects to the dimmer come from? The headlight switch? A relay?

Thanks in advance.

Alan in AZ · 02-26-2008, 03:02 PM

Yes it can - the lens pivots about the middle of the long axis - just press hard either side of the lens. Same all years

Alan

rjm65 · 02-26-2008, 10:33 PM

Ok I see it now. I was thinking you meant the entire lense slid back and forth, but after removing the switch from the car and seeing how it's hinged in the middle I understand now. Thanks!

Landseer · 02-28-2008, 06:38 PM

Are you sure, Alan, on "B"? I just crawled under the dash and the 84 at least has a bulb holder that fits into the right side of the cover under the steering column.

Alan in AZ · 08:44 AM

Even on an '84 - I am unaware of any underpod lights - if you have them they may be aftermarket... It does not seem to be a location that would really work very well as a map light anyway.

Anyone else have this?

Alan

Danglerb · 02-29-2008, 12:54 PM

Quote:

Originally Posted by Landseer

Are you sure, Alan, on "B"? I just crawled under the dash and the 84 at least has a bulb holder that fits into the right side of the cover under the steering column.

How about a picture?

Another thought, loose under dash bulb holder, no telling where it might have originally been attached and to what.

Landseer · 06:44 PM

I have a couple photos, but it's not much different than the one above.

Here's what I found. It was mounted where I said in the rightside lower part of the dash. The removable cover under the pod has a cutout for it, but it mounts in the lower part of the pod/dash.

It didn't have a bulb, and I couldn't figure out what it would use. With key on, the two electrodes had battery voltage across them, then, whammm, the wipers wiped a few times and quit. I repeated. Sure enough, again. So, this is a base remnant of an under-dash switch that "bumps" the wipers a few times.

( Does this sound a bit like the 'what is it" portion of "Ask This Old House"?)

This actually makes more sense than having a crotch light.