Headlight Switch Short?

[81L81]

Maybe someone can help. When I turn my headlights on, my temp gauge needle goes off the charts, litterly gets pinned. When I adjust the light switch all the way down the temp gauge returns to normal.

Any Ideas?
I ordered a new switch hoping thats what it might be.
Any recommendations on installing the new one?

Thanks for your help.

 

[jdp6000]

Thats a new one. Do you have a dimmer on that headlight switch? There are two parts...dimmer in front and headlight control at the rear. does it work?? This problem...does it happen only when the headlights are on or also when you set it so JUST the marker lights are on?? If it happens in the market light setting and the headlight setting. i think you problem maybe in the plug at the rear of your center cluster. I say this because when the switch is pulled you power the guage cluster lights. The circuit behind your guage cluster for the lights is near the circuit for your temp guage. Its just a copper printed board and it does break or shift. So if this discription fits...pull the cluster and look at how the temp guage sits on the printed circuit board.

Now if it only happens in the headlight postion and not in the market light position.It sounds like the power wire for the temp guage and one of the wires from the headlight switch are touching. The temp guage works on voltage. When you pull the headlight switch you send power through a wire...12 volt...it seems that this power is then being sent to your temp guage . You never know though...

Headlight switch is a bit of a pain to get out but you can do it. Remove the dash cover under the steering wheel area so you can look up. Unplug the wire harness and vac lines. There is a pin you need to compress to pull out the shaft and knob. Once the shaft and knob are out...remove the trim plate...etc and the switch will drop out. Reinstall in the reverse.

To those that have never done it before I recommend the following...its only so you can see better. You maybe able to do it without the following proceedure. Loosen off the dash pad (the part your speedo and tach are in)...there are a couple of screws on the bottom and a couple on the side near the door pillar...enough so you can pull the dash out so you can see the switch from the side.

Jim

 

[81L81]

Thanks Jim,

It only happens when head light swith is on. I think you are correct to say that some wires may be touching or the circuit board may be shorting. As you adjust the dimmer switch to high or full the temp gauge goes up, as you turn it down gauge needle goes down. Its almost like I am adjusting voltage to the temp gauge.

Thanks for your help,

Tom.

 

[jdp6000]

Sounds like your switch is fine...

It definitely a cross somewhere at the rear of the cluster. The copper circuit terminates where the harness plugs in at the rear of the cluster. It gets twisted up sometimes. I think you should take out the cluster and carfully examine the circuit board. Once out you can plug the harness in and play around.

Its easy to get out. couple of screws on the left... a couple on the right. don't miss the two that hold it to your console plate. You need to remove the covers on both sides of the consol to see these two. Most miss them and snap the plastic.

Jim

 

[jdp6000]

If you are going to do it change the bulbs while you are back there. Maybe lube some of the heater/AC connections.

Jim

 

[81L81]

Thanks,

Will check circuit board.

 

[jdp6000]

I should have added.

If you do take it out follow the copper on the circuit board from the temp guage back to where the harness connects. Easiest way to find the problem.

let us know if you find the problem.

jim

 

[Mr. Chuck]

The dimmer function of the the head light switch appears to be operating correctly since the problem seems to go away when you rotate the dimmer full CCW and since the dimmer should only vary the instrument light brightness, the problem is most likely at the connector at the rear of the instrument cluster or in the panel circuits. I would first look at any recent work done related to having the instrument cluster out or electrical connector(s) off & on. My 81 shop manual shows the only common link between the light switch and temp gage is the dimmer function and it connects directly to instrument cluster. i.e. a new switch doesn't seem indicated. This kind of problem normally doesn't come from component failure, more from human activity related to service efforts. The idea of flex circuit alignment or damage my be the cause. If you need selected copies of the manual, send me e-mail and I will reply with info.
Regards:

 

[81L81]

I should have added.

If you do take it out follow the copper on the circuit board from the temp guage back to where the harness connects. Easiest way to find the problem.

let us know if you find the problem.

jim

Will do. Talk to you soon.

Thanks again

 

[81L81]

Thanks Mr. Chuck,

You had helped me with a problem with my light switch and temp gage a few weeks back. I ended up replacing the gage circuit board after finding a crack in the copper contacts and everything works great.

Thanks again for your help,

Tom

 

[81L81]

Jim,

you helped me trouble shoot a problem with my temp gage and light switch and as you suggested there was a problem with the gage circuit board. There was a crack in the copper contact where the plug plugs in. I replaced it and everything works fine now. Thanks again for all your help.

Tom.

 

[jdp6000]

Just received notification. I replied to your email....

Jim