Hi all. I just introduced myself in the Newbie forum. As of two weeks ago, I'm the proud owner of a '69 Cutlass S convertible.

The instrument panel lights don't function. My guess is that it's the headlight switch rheostat or possibly the wiring from rheostat to the lights. The lights hadn't worked in the short time I've had the car, but then two nights ago the light for the fuel gauge illuminated faintly (the light for the speedometer stayed dark). Then last night, nothing.

I have a multimeter and have checked out what I can so far.

• The 4 amp fuse is fine (not just visual but with multimeter too)
• The fuse terminals are good. They could be a little cleaner but they carry current (checked with multimeter)
• I haven't had a chance to check the wiring from fuse box to panel, the bulbs, or anything else behind the dash.

Everything else on the headlight switch works. Turning the rheostat to the right and back doesn't dim/light up the panel. Turning it all the way to the left turns on the dome light.

If anyone has suggestions, I'd really appreciate it. I have copies of the original '69 chassis and Fisher body service manuals, so if you point me somewhere I can look it up. I'll be happy to buy a new headlight switch, but the fuel gauge dash light coming on threw me for a loop. Maybe the rheostat is fine and it's a wiring issue? Hoping to avoid removing the instrument panel itself, for obvious reasons. Thank you.

 

What is the voltage on both sides of the fuse with the headlights on and the rheostat turned to the left?

 

Thanks for posting. Can you please clarify "due"? If you mean the voltage coming into the 4 amp fuse terminal and then the voltage exiting on the other side, I don't know but I'll check tomorrow.

Minor clarification: being a convertible, there is of course no dome light. Turning the switch all the way to the left lights up the map light and a passenger side light.

 

A couple of possibilities: Assuming all wiring and connections in this circuit are intact, either your dimmer rheostat is bad or multiple (all?) bulbs in the dash are burned out. A way to check for which is bad, bypass the dimmer by connecting +12V to the bulb-side of the rheostat. This can be done at the switch (consult your wiring diagram for wire color). I'm pretty sure that this node also connects to a wire going to the radio for its back-light, which dims as well with the dash lights. This wire may be easier to get to. Either will work. If your dash lights come on when this node is connected to +12V, the rheostat is bad, if they don't come on, you'll have to tackle the bulbs in the dash (or possible bad connections going into the dash).

 

I meant fuse. Turn the rheostat to the left and stop before the dome light detent. Also check the tail light fuse as that feeds the voltage into the switch.

 

The headlight switch in those days carried and dealt with fairly high amperage to feed the headlights and other bulbs. It’s not uncommon to see melted insulation and partially melted plastic shells on the wiring connector that goes into it. The ceramic heat sink that the rheostat wire sits inside sort of tells the tale about how much heat these switches had to deal with.

In the 60’s & 70’s Olds used a wiring connector system called Packard 56. You can still get the male and female spade terminals to repair damaged wires and you can get the plastic shells too. See AuVeCo for these parts.

Another place things get dodgy is the ignition switch. Again high amperage sometimes melts the wires.

This is all leading to a humble suggestion that if you have the time, patience and inclination consider pulling the entire wiring harness from headlights to the dash and repairing it on the bench so you have a solid electrical system. One of the best fixes I ever did.

I can’t get replacement harnesses for my ‘66 big cars, but for Cutlass/442 in popular years there are replacement harnesses for sale. Check with the experts here about who makes the best ones.

You’ll find the problem. These were robust systems back in the day and usually finding the problem is 80% visual inspection.

Good luck!
Chris

 

Thanks for the input, everyone. Been a busy few days and couldn't get back to this right away.

The dash lights (fuel gauge and speedometer) now illuminate, but are rather faint. The maximum (rheostat turned left) feels like it should be the minimum. The minimum (rheostat turned right) dims to off. There was no optional clock installed, so I'm guessing no dash light for that unused display; if there is one it doesn't work. Turning the rheostat all the way to the left activates the map light as before (convertible so no dome light).

Steps leading to this result:

I checked the fuse voltage again. With headlights on, I got results from 0.14V to 2.00V but I may done it wrong. This was done with the multimeter leads touching each side of the terminal. It was late and hard to wedge myself properly to get at the fuse box.

After a good night's sleep, rereading everyone's comments and my multimeter instructions, I tried it again. This time I touched the positive to the fuse terminal and the negative to metal. With the lights on and the rheostat to the left I got 15.7V. With it turned fully to the right I got 0.25V. I disconnected the battery, removed the 4 amp fuse and gave the terminal a scrub with a wire brush. Put in a new 4 amp fuse, reconnected everything, and got better results. BTW, the old fuse still doesn't appear blown, but it is definitely tarnished and dirty next to the shiny new fuse.

Any thoughts about the dash lights working but looking dim even in max position? Again, turning the rheostat right/left does dim/brighten. If it's not the bulbs, fuse or rheostat, maybe a corroded wire leading to the actual bulbs is provided some resistance?

Thanks again, everyone.

 

The rheostat goes bad. I've had this happen on more than one car. You can test for this by unplugging the connector to the headlight switch and jumper the brown/white wire in the connector to the green wire. If the dash lights come on at full brightness, replace the headlight switch. If not, trace those wires and find the problem. Also verify that you have battery voltage from the brown/white wire to ground.

 

I"ll try it. Thanks, Joe!

 

Thanks for the information, Chris. I think pulling the wiring harness is above my current skills, but your (and everyone else's) information has been really helpful. I'll take this as far as I can. If I can't fix it, a family friend owns a classic car restoration business about 40 miles away. Once my list of "tried but failed" fixes is long enough, I'll have him take a look. I just don't want to leave my "new" car with anybody at the moment!

 

I see you're in LA, SoCal is part of the desert Southwest. The rheostat coil can get coated with dust that will interfere with the dimmer voltage, but since you are getting a range of voltage across the fuse that seems unlikely. Just to be sure, twist the **** back and forth rapidly several times. It may or may not help. You may just have corrosion on the small dash light socket connections. Been there done that. Find the grey wire behind the dash that feeds the ash tray or radio light and make sure you have voltage there. It should be the same as you measured across the fuse. If you have an aftermarket radio, it happens a lot to have that grey wire used as a ground wire. That usually pops the dash light fuse, but not always.