Dim Dash Lights

[laffeaux]

The dash lights on my car ('71) are really dim. The bulbs are new. The brightness adjuster goes from "off" to "barely on." Could this be the fault of a bad adjustment switch? Are they hard to replace?

[2ManyZs]

More than likely it is the rheostat, not too hard to replace, if you can get your hands in there to reach the backside of it. :tapemouth

[skip260z]

On your back, head on the brake pedal, the Z owners Yoga.

IIRC, these bad boys are NLA. Pull yours and check it with an ohmeter, you should see the resistance move as you spin the stem. If so, it ain't the rheo.

Next thing to do is to get the spray electrical contact cleaner and find every, EVERY connector you possibly can, and clean, reconnect.

Then do the same with the fuse box.

Battery disconnected of course.

[EScanlon]

The rheostat (dimmer) is screwed on to the bottom part of the dash on the metal pan. There are two phillips head screws holding it in place. If you can get your hand up there and then find the screws and THEN get them off, well you're either a contortionist, or you have very small and agile hands.

Since the rheostat basically has an exposed coil, these tend to accumulate crud and oxidation on the contact surface of the wire coil. When the wiper contact slides over it, it has a lot of resistance due to this crud and you have very little juice that can make it past that.

To check if in fact it is the rheostat, reach up there and disconnect the two wires going to it. Then connect them to each other, i.e. short out the rheostat. If your lights then light up brighter than what you had, then it is the rheo that needs cleaning / replacing. It is relatively easy to fix / clean and get it working. The PITA is to get it out of the dash so you can do it.

If the lights however, DON'T brighten up, then you have a problem elsewhere. But I don't think that's the case here.

[laffeaux]

The lights definitely dim when the knob is turned - they go from off, to barely on (and anywhere in between). I'll try to short it out and see if they are brighter.

[skip260z]

To tell you what the dash lites look like while you are down there shorting the 2 wires together, as you will not be able to crane your neck up and see the dash lites. BTDT.

What I did was with lights off, shorted (bypassed the rheo), then came up for air and then twisted the light stalk to turn 'em on - - - before I could say sh*t, I had a tiny wisp of smoke... Luckily nothing damaged.

I think that the rheo is supposed to add some very minor baseline resistance even when "off" (that is, brightness to full), and by removing from the circuit you allow the full current to flow.

Just be fast on the twist stalk and you should be OK.

And as the other poster said, douse that rheo (and all connecters) with electrical contact cleaner. I sprayed my rheo till it was running out of the seams. Let it dry, and connected with new bulbs - it was thne finally acceptable.

[EScanlon]

Where did you get smoke coming out from?

The rheostat adds resistance to the circuit only when it is turned down from full brightness, as that IS the method it uses to dim the lights. When you turn it from OFF to Dimmest position, you are adding the maximum resistance it can. When you turn it to the full brightness it is essentially bypassing the resistance coil.

[WillieBoy240z]

Yeah, what EScanlon said....

This is fresh in my memory because I just removed the whole dash on my 72 and removed everything -- including the dimmer switch. While most of my components looked very clean, the dimmer was kind of corroded. My lights are dim like yours as well.

I think you can test and clean it up as instructed and it should work fine. If you went to the trouble of replacing the bulbs, then this should be a piece of cake in terms of access.

Disconnect the battery before you mess with anything electrical. Trust me -- I learned this "the hard way" a while back. I am happy to report that battery acid getting into your eyes after a shorted battery explodes does not always cause blindness as long as you can wash out your eyes within 10 seconds. This I know.... :-)

[EScanlon]

If you've maintained the Engine compartment wiring harness pretty much intact, there should be a fusible link connector going to the starter motor from the battery. Disconnect this and you disconnect the REST of the car from the battery.

Even though you still have the engine connected, you have the complete ignition circuit disconnected. Check your wiring diagram and you'll see what I mean. It works.