Instrument Lights

[Jimjific 23]

Ok, I've got a weird one here.

 

I've been doing a bunch of interior stuff so I figured I'd look into why my instrument lights don't work.

 

Here's what I know:

- Lights never worked from the day I got the car. ~1.5 years

- When I first looked into it the fuse was blown.

- I replaced the fuse and they still didn't work.

- Since I have dash apart I tested the connector.

- At the time, I found the contact that lights the lights and it worked with the switch and I could see the voltage change as I rotated the switch.

- I could get a bulb to light by hooking up leads to it.

- Finally got back to working on it last night and couldn't get anything to work and couldn't find the voltage from the switch.

- So I checked the fuse and it would ring out with the meter.

- I check the terminal on one side of the fuse and I see 12V

- I check the other side and I don't see anything.

- At this point I'm like what the hell? I check the fuse again and it rings out again.

- So I pull the fuse and it is blown.

- I check the terminals again and 12V on one and nothing on the other.

- So I put the probes on both terminals and check continuity and it rings out with the fuse gone.

 

How can this happen?

 

I hate electrical problems.

 

Jim

[LoneWolf2U 136]

The probability of a pinched/bare wire somewhere in the lighting circut.

The fuse keeps blowing for a reason.

[69RavenConv 286]

The probability of a pinched/bare wire somewhere in the lighting circut.

The fuse keeps blowing for a reason.

 

+1 The printed circuit can be shorted to chassis by the mounting screws, too.

[danno 128]

Yes, the flextapes on the instrument panel often can short to the chassis right behind it. Remember that even with the instrument panel disconnected, the easy way to see if the fuse and wires are good is to look at the light for the heater contol. It is on the same circuit, so if it works your fuse and most of the wires are ok.

 

I would start by removing all 8 of the bulbs that light it up, and look for one of them that is different from the others. If you have some alligator clips and a batery charger, hook voltage up to the flextape where the lights connect, and plug in the lights one at a time. If you can do all this and the lights work, report back to us for the next step.

[Jimjific 23]

Thanks for the replies. I will have to try the battery charger idea. One thing that is really confusing me is, why does is there continuity between the fuse terminals when there is no fuse in it and the flex board is disconnected. Also, the fuse terminal rings out to ground. Would this indicate a bad headlight switch? Just so you know, this is the only thing that doesn't work on the car.

 

Jim

[Midlife 814]

Thanks for the replies. I will have to try the battery charger idea. One thing that is really confusing me is, why does is there continuity between the fuse terminals when there is no fuse in it and the flex board is disconnected. Also, the fuse terminal rings out to ground. Would this indicate a bad headlight switch? Just so you know, this is the only thing that doesn't work on the car.

 

Jim

If both fuse taps show continuity to ground without a fuse installed, then you've got multiple problems. Power runs from the headlight switch to the fuse box, across the fuse to 8 or so lamps. I suspect that one of the bulbs has a short to ground, and that is what is causing both fuse taps to read continuity to ground when a new fuse is installed but before you power the lamps up. As soon as you do that, the fuse will blow.

 

I like the idea of removing all bulbs and testing them one by one. Eventually, you should find the general area where something is catywhompus.

[Jimjific 23]

Ok, I guess I must have not stated things well. I have the instrument panel disconnected while I've been doing my recent debugging so the flex circuit is out of the picture for now at least.

 

All of this is with NO fuse installed.

- With the switch off both fuse terminals read 0 volts.

- With the switch on I see voltage (~11V) on one of the terminals (good)

Here's what I can't get my head around.

- When I check continuity between terminal it rings (Again no fuse)

- When I check continuity between either terminal to ground it rings also.

 

So this means that when I turn on the headlights the instrument panel lights are sending ~11V to ground. So why isn't anything burning up?

 

Also, with the lights on and checking voltage, as I turn the switch shouldn't I see the voltage drop? Right now it seems like it bounces and then settles back to 11 but not always. If I turn the it all of the way to the low light position it goes to very low voltage.

 

I printed out the schematic. I will check if the heater control lights works tonight. I believe it is out though.

 

The shift select works but from the schematic it is on a different circuit.

 

Thanks for the help,

Jim

[danno 128]

The continuity measurements are screwing with you. Continuity is measuring correct, but that is not working for what you need. You measure the continuity from across a light bulb, and it will look like a short. Yet you put 12 volts on it, and it lights up. When you are doing the continuity measurements, you are essentially measuring across the light bulbs in the circuit. You have to unplug all bulbs on a circuit to check continuity. And that means almost every bulb on headlights circuit to allow a continuity check. So don't count on that.

 

Also, when you turn the switch, you will see the voltage drop if everything is normal and connected. Without the instrument panel lights NOT connected, you will not see the voltage drop as you turn the knob.

 

If you need to check continuity of the instrument lights circuit, do so with the fuse out. You have to unplug the heater switch light, radio light, and clock light ( if you have one). Then measure contunity, and it should be good.

[Jimjific 23]

Danno,

 

With the headlight switch in the open/off position and the fuse removed from the the fuse block the downstream circuit is broken and the instrument/heater/clock lights should have no bearing on continuity. Yet, when I probe either terminal it rings out to ground. The "down stream" one makes sense since it could be going through the heater bulb to ground. It is the "up stream" one that has me confused. If it is grounded when the fuse is removed why don't I see sparks when I energize it by turning on the headlights?

 

I think I need to take the switch out and see if there is an issue there.

 

Thanks again,

Jim

[Midlife 814]

Danno,

 

With the headlight switch in the open/off position and the fuse removed from the the fuse block the downstream circuit is broken and the instrument/heater/clock lights should have no bearing on continuity. Yet, when I probe either terminal it rings out to ground. The "down stream" one makes sense since it could be going through the heater bulb to ground. It is the "up stream" one that has me confused. If it is grounded when the fuse is removed why don't I see sparks when I energize it by turning on the headlights?

 

I think I need to take the switch out and see if there is an issue there.

 

Thanks again,

Jim

 

Yes, if the power side of the lamp circuit fuse has continuity to ground, then you do have a problem. That wiring is relatively simple. The headlight switch provides power to the fuse box through one wire running between the headlight switch and the fuse box. I'd disconnect the headlight switch from the harness and then check for continuity to ground on the power side of the fuse box. That will let you know if the problem is in the headlight switch or in the wiring.

[Jimjific 23]

The frustration continues...

 

- I've isolated the wire that supplies power from the switch to the fuse block and all seems good there. Pulled the light switch out.

- I've also tested the gauge cluster lights using the battery and there is nothing wrong with the flex circuit.

- So I put a new fuse in (With the gauge cluster removed as well as the heater light and I have no clock)

- As soon as I turn the light switch all of the way to max, the fuse blows. I Had another switch and tried that one and got the same results.

- I assume my issue is between the down stream fuse terminal and the wiring that feeds to the gauge connector.

- One weird thing I can't understand is with the fuse block pulled from the fire wall I checked continuity between the down stream fuse terminal and the contacts on the back side of the fuse block and it rang out when I touched the 12V main source pin.

 

I'm getting really tired of spending what little time I have on this. I am getting nowhere on the car so it just sits. I'm getting to the point of cutting out the instrument lighting wiring circuit and making my own.

 

Jim

[danno 128]

The wire for the intruments lights goes from the switch to the fuse. After the fuse, it goes to these places

-instrument panel

-heater swithc light

-radio panel light

-clock light

 

The clock light connector is above the glovebox, it is a blue with red strip wire. The radio panel light connector is on the left side of the glove box. Make sure neither of these is connected to or touching ground.

 

When you put the fuse in and it blew, did you have anything ( like the instrument panel) connected? I know that the instrument panel tested ok when it was removed from the car, but just because it worked when removed does NOT mean it will work when reinstalled. The instrument panel can have a short between the +voltage and the metal frame it sits in. This short between the + and case will not cause any problem with it is removed, but as soon as you re-connect everything, it will blow the fuse.

 

So assuming you have absolutely nothing connected, and you still blow the fuse ( or measure it as low continuity), then you have a bad wire somewhere. Start at the 5 ends mentioned above, and follow it back to the fuse block.

 

You might have some work done be a previous owner that might have been some modifications to the factory wires. Look for the radio connector, that is where it often happens when an aftermarket radio is installed.

 

Do NOT cut the panel wires and make your own. It is frustrating, but take it one step at a time.

[Jimjific 23]

Danno,

 

Yes the instrument cluster is disconnected as well as everything else that I can tell from the schematic.

 

Jim

[Jimjific 23]

Danno,

 

Success!!!!! So I went to work on the car and figured I'd do something I knew I could get done to get some positive vibs. So I got the inside quarter panels back in. With that done, I switched to looking at the dash lights again. I re-read your last post and said to myself, I will look at the clock wire. I previosly hadn't looked at it since I don't have a clock. Well wouldn't you know, the previous owner had the glove box light switch plugged into it. I unplugged it and checked to see if the down stream fuse terminal rang to ground and it didn't! So I plugged it back in and did the same check and it rang to ground. So that was shorting out the circuit. I put a new fuse in and plugged the headlight switch in and no blown fuze. I just plugged the instrument panel in and it all works.

 

Victory feels good. Thanks for everyone's thoughts on this. I am a way more mechanical guy than electrical guy.

 

Jim