Interior Instrument Light Rheostat

[erectorset]

It's Father's Day today and I decided to replace the interior instrument light rheostat on my 1971 240Z (manufacture 6/71) with a used one that I picked up on eBay. The original rheostat stopped working long ago and the instruments lights are dim. My hope is that the replacement rheostat would solve this problem. What I thought was going be a simple swap turned out to be a an excursion into the nether reaches of the dash. It appears to me that the rheostat is in a totally inaccessible location and that the swap can only be done if the dash is removed. I read EScanlon's 2/12/2002 Post on this matter and he says you can get a 90 screw drive and there and loosed the two phillips head screws. Another person said that you need to remove the driver's seat to get back behind the dash to do the work. Compounding my problem is that the shaft that the black plastic knob slips over is loose and now that I pulled the black plastic knob off I can no longer get it back on. It would appear that either the phillips head screws are loose or missing because I can slide the metal shat up inside the dash foam. Lastly, the replacement rheostat that I got was supposed to be from a 1971 Z. It matches up somewhat to the picture in my original Service Manual which is very dark. It has two wires, one male the other female. The wires are both red with a blue stripe and are each 2" long. Feeling around in there has been of no help as I cannot touch even the rheostat and the wires that are visible appear to require longer leads than what I have. My questions are:

1. Has anyone done this swap recently? Do I really need to remove the driver's side seat and purchase some type of 90 degree screw driver?

2. Are the phillips head screws above the mounting plate or below it? If they are below it the underside portion of the insulated dash would be in the way.

3. Do I have the correct part?

Any advice would be appreciated.

[Terrapin Z]

I have never do the job myself, but looking at my spare dash it looks like a 90 deg. screwdriver or a vert short stubby might work. with some patients

Sounds like you have the correct part, my dash if from a mid 72 car.

Here are some pics of it from the top side.

I hope these help, good luck!

[MikeW]

The original rheostat stopped working long ago and the instruments lights are dim.

I hate to break it to you but it's possible that even with a new rheostat the lights will still be dim. A rheostat is just a variable resistor and you can simply bypass it to see how bright the lights will be with a working rheostat turned all the way up. You may find that you've got some burned out bulbs and others that just don't measure up. New lights may be in order.

[EScanlon]

Or it may be that the knob that rotates the contact on the rheostat has broken off the plate and that is why he only has the dim setting.

If the Rheostat had burned out, or the wipe contact had bent out of shape and no longer contacts the spiral wound wire he wouldn't have any dash lamps at all.

The pictures that Terrapin Z provided show the rheostat well. Those two phillips screws and the knob on the underside need to be removed before you can push the rheostat UP into the backside of the dash to remove it. Part of the problem in pushing it UP into the backside, is that the Tach itself, and the Hazard Switch wiring can get in the way.

Mike is correct in that you can simply connect the two wires going to the rheostat to get an idea of what the brightest setting would be.

Removing the drivers seat isn't a must, but it certainly does help not having to contort yourself between the seat, the steering wheel and the foot pedals in order to lay down on the floor to be able to get your hand up and behind the dash to get the little bugger out.

The reason for mentioning the 90° screwdriver is that even a short 1.5" stubby will be difficult if not impossible to fit in there. I used a 90° and was able to do the job... some years back which is when I wrote the post. One of those small handles that hold a P2 Screwdriver bit would also work and you can get a set of those at Harbor Freight for a buck or two.

When you look at Terrapin's photos, the one on the right shows you the backing plate for the Hazard Switch and Cigar Lighter which should allow you to "see" what you're working on.

HTH

E

[erectorset]

Guys: Thanks for your responses and the pictures. First, my instrument lamps are all working but dim when the car is running. Both the old and new plastic knobs are not broken. If the instrument lamps stay dim with the rheostat turned up then so be it. I won't know until I put in what I hope is a functioning rheostat. Since I made the post yesterday I went back to the car and reached up further behind the dash. I was able to reinstall the plastic knob by pushing down on the top of what I thought would be the rheostat but felt like a cable attachment to the top of the metal rod which the plastic knob attaches to. This cable goes somewhere else which I could not determine. My dimmer switch is to the left of the steering wheel when I am sitting inside on the driver's seat and looking out the window. My Hazard light swith is on the other side of the steering wheel and my cigarette lighter is in the console below the ash tray. Could I have an older set up with a remote rheostat somewhere else? I was also able to feel a wing nut. Is this wing nut what attaches the tach to the braket shown in both pictures? My next move is to get a probe light and some mirrors to find out what I really have. I will get back to everyone when I do.

[zKars]

Aha! That is your trip-odometer reset knob to the left of the wheel! There is an identical knob on the RIGHT side of the steering column under the dash that is your dimmer rheostat! That cable attached to the left hand knob is attached to the back of the speedo. No wonder you were confused!

Jim

[erectorset]

Jim: After 39 years of ownership it is easy to forget. I am embarrassed. I will now look on the right side of the steering wheel.

[Gary in NJ]

We're all laughing with you, not at you.

[Z train]

Be advised there are different wattage bulbs available.