I have been having peculiar incidents with the operation of the headlight switch, at least I believe that's the culprit maybe someone can confirm that. I recently noticed when I turn the lights on, the red lamp indicator dash light stays lit and doesn't go off. Then I noticed, with the lights off and in down position if I turn the ignition switch to on position the tachometer lights up and stay lit and when I pull on the headlight switch the speedometer lights go on and the headlights come up as expected.

Could there be a short in this switch ? Thanks for any input you may have. Fred

 

The headlight switch has a ground strap that runs to the back of the speedometer then that is gorunded to the harness with a tab and a wire. I'd look at those grounds, and the cluster ground just above the hood release handle bracket on the pillar.

As far as the headlight warning, those switches are flimsy. Adjustment or could be broken- after all look at the age of them.

 

Sometime ago I checked the ground in back of the speedometer which was a black wire 16 gauge that was grounded to the pillar beam or frame.
As you suggested these are old parts so I guess I'll start with the process of elimination. Switch first. Thanks

 

Your light in the dash that says HEADLAMP is controlled by the limit switch on the front of the actuator linkage. This switch was a poor design and breaks quite often. This is what Tim is talking about.


The other problem and what Tim is referring to is a metal strap between the headlamp switch and the speedo housing. This is a metal strap and not a wire. It could be corroded or not making good contact. This really does not sound like the headlamp switch. The lamps in the tach and the rest of the dash lamps are all on the same circuit. Something is back feeding voltage to the tach lamp.

I don’t know what it could be and maybe someone else has a suggestion, but you should not have voltage on the tach lamp wire and it is indicating a back feed situation which is most often caused by lack of a ground.

Willcox Inc.

 

Much appreciated thank you for that info. Fred

 

Is there any where I can get a detailed picture of the rear of the tach and speedometer so I know what to look for in hoping to correct this problem
Thanks, Fred?

 

a metal band going from the speedo housing to the light switch.
as usually crappy rusty connections, are not acceptable.
again GM's crappy gnding method. 68VETT

 

The red metal ground is what they are talking about, it goes under the blue screw too!

 

I have a question for those leaning towards the headlight ground strap (in red on above drawing) as the cause of the problem. What are your thoughts as to what is lighting ONLY the Tach bulbs ?

My thoughts are that the red strap is the ground path for the the courtesy lights and would have no effect on ONLY the tach bulbs.The strap is attached to the speedo.

Strom19--- Are all the illumination bulbs in the tach lighting up or could it be only 1 bulb like the park brake bulb that is in the wrong hole ?
Is the wiper solenoid mounted to the tach case (where its supposed to be) ?
Could you have left the black 14 gauge ground wire off of the tach case ?
Do you remember connecting the brown 12 gauge wire to the capacitor on the ignition switch ?

edit-is this a new problem or did this come after reinstalling the dash ?

 

Dwncchs, I'm sort of on the same path. Something has to be feeding voltage to the bulbs. I don't think this problem is the headlamp switch. I think it is something back feeding voltage. I just posted the picture so the OP would know what Tim was talking about.

The concern would be why just the tach bulbs? Are the bulbs glowing or are they bright?

The gray wires that feed the tach bulbs also feed the rest of the dash lamps so the selectiveness of the tach is not making any sense.

 

the head light gnd strap is only used to complete the Dome light circuit Gnd..
no affect to the outside lights.
69VETT

 

I am overwhelmed with questions and suggestions and I really appreciate all the help that has been pouring in regarding my problem.

I can honestly say it all began when I replaced a tach cable and shortly after that I noticed the brake light pulsating on and off when the ignition was turned on. It was suggested that a ground was the culprit so I took the panel down and began looking for anything that didn't look right. Well to be honest everything under that dash didn't look right as it was all foreign to me anyway. I did however have enough sense to see if I disturbed any thing in my tear down. I looked for possible torn ground wires etc. but did not notice anything unusual that I could have caused. I proceed to check that bulb & connector and try to place it back into the socket hole. It seemed to resist seating properly so I spread the tabs on the ground part of the bulb in order it would snap and hold in place. When I finished I tested the bulb for pulsation buy turning the ignition on and to my surprise it continued to do the same, so I just pulled the connector with bulb and tied it up around the harness neatly and button things up. My first indication was the headlight stem when pulled out for parking lights only did not have a click or a position space for that function so I had to pull it out just a tad or else the headlights would go up. It was just the other day when I replaced a wiper door actuator located under the right side fender scoop that I turned the Ignition switch on to activate it when I noticed that the tach lights were on only and then when I continued to pull the headlight switch on the speedometer lights came on . To answer one of the question regarding the brightness of the tach bulbs, yes they seemed to be brighter. Well I hope one of you catch this posting if any of that makes sense what may have happened. Thank you you all again, Fred

 

Your suggestion was a very good suggestion and I agree. . Possible! The only way to find out is to run a jumper ground and test.

What is confusing about this is why just the tach bulbs?

The selectiveness of the tach lamp bulbs is not making any sense at all.

Maybe this is a back feed low voltage problem from no ground. My thought on this would be that the voltage is so low the tach bulbs get enough to light up but the drop from the tach bulbs lighting is causing enough drop that the other lamps not. . . . . I hope this makes sense!

Unless someone has done some fancy wiring in the dash this would be about the only explanation that I can think of.

Willcox

 

I wish I was at home so I could go out in the garage and do some experimenting but right now I'm sitting in a Motel 6 in Macon Ga..
It seems to me I remember getting shocked from an unmounted wiper tach solenoid. It could have been a bad one but they might all act this way.
But if it wasn't bad and the solenoid can backfeed through the case this might be the power backfeeding through the tach head if the black ground wire is not attached. The tach bulbs would be using the other bulbs in the speedo for a ground until the headlight switch is turned on. This might explain why only the Tach bulbs are being effected.

edit-- Oh and yes they left the light on for us.

 

Catching up on the discussion I would like to reiterate that everything worked fine up until I replaced the Tachometer cable and by doing so pulled the panel in order to to get to the cable. In short ( no pun intended) I must have disconnected or broken a lead some where behind the speed o and tach. If I had a photo diagram of a complete working system I then could possibly see whats out of order. If I had the following manual would it help me achieve that? http://www.helminc.com/helm/product2...EDU03TT0PK32PC

 

Here is a picture of the wiring circuit.



Roger, if the solenoid was shorted out and mounted to the tach can it could cause this by shorting power to the metal can. Interesting thought.

You might up-plug the tach solenoid and see if the problem leaves. Or you might probe the metal can and look for current.

Willcox

 

with only the tach lights glowing something is shorted and/or open against the tach housing,
back-feeding thru the tach lights to gnd. I would suspect the tach housing gnd wire is not connected.
process of elimination, when you do not know what the problem is, start unplugging thinngs until the problem goes away.Not random unplugging, know what you are unplugging, tackle 1 problem at a time, at this point repost your symptoms please.

 

Thats why I mentioned the wiper door solenoid that is usually mounted to the tach housing. The solenoid works fine just hanging (as most seem to be )but I wonder if when not attached to ground will it backfeed current ? As I said earlier I've got shocked by the tach solenoid when engaging the wipers.

Another item I mentioned that could "power up" the tach housing is the brown wire that is supposed to be attached to the radio suppressor or condenser on the side of the ignition switch.
If this wire was mistakenly attached instead of the black ground lead this would most definitely apply 12 volts to the tach housing. The wire is dark brown and has the same female connector as the black grounding wire. Its just a thought and most likely not the case because if the tach cable was connected would send the brown lead directly to ground blowing the fusible link. Strom is your tach cable hooked up ?

 

The Wiper Solenoid was never attached to the tach even when there were no problems It's just the way It was when I purchased the car, just hanging. I'll get into it and try to post some photos and check those connections.

 

The tach cable is hooked up and that brown lead is connected to a thinner black lead by way of plastic matching connector which on the end hangs a condenser. Because of site rules I am unable to show photos of under my dash. I haven't pulled the dash face so the only access I have at the moment is under steering column. Everything else that was asked seems to be in order.....