[gonec0untry]

Before you comment, please note I've spent days searching the forums to try and find my answer. No such luck.

I have a 1970 Chevelle that I am doing the SS conversion with. I've installed the correct wiring harnesses and have been able to get everything to work (after a lot of work. Grounds are a bi*c*h) except for two items.

First- The dome light only works when the door is open. It will not operate when using the head lamp switch by twisting it. It's brand new.

I took a 12v tester and tested the white wire coming out of the head lamp switch and it's dead in all positions. This is where I need YOUR help to confirm that I think the BRAND NEW head lamp switch is bad.

When I twist the knob all the way to make the dome light turn on, should i get power out of the white wire??? The orange wire seems to always be HOT. I appreciate your help on this one.

Second - (which may be related to the first) I have an HEI Distributor. My tach doesn't seem to work properly without the head lights being ON. When I turn the head lights off, the tach idles around 1k rpm and when I give it throttle it goes down to zero. When I turn the lights on, the tach works better, but not sure it's 100% accurate. It goes up to about 3k when goosing it in park. It's not road ready so I can't drive it around the block to further test the tach with the lights on.

Do you think the headlamp switch is causing it to only ground when the headlights are on? Before I put the dash in I tightened all the nuts and bolts on the back of the gauges. My gauges came as a kit with everything installed on the cage. The only nut I didn't check (thinking I should have) is the one under the circuit breaker that doesn't have a nut on top, only underneath. Is that the tach ground? Can I do an external ground? which post would I attach the wire too?!?

I'm still wondering if this problem is related to the possibly broken headlamp switch.

I remember reading a forum about the tach where someone had a similar issue, but that was months ago and now I can't seem to find it.

Any advice you can give is GREATLY appreciated.

 

[azchevs]

Do you have the ground strap that goes around the front of the headlight switch down to the bottom metal structure on the dash. Here is a link to a photo of one http://azchevs.com/images/misc_053.jpg. There should be 3 black ground wires that meet up under the cluster area, they come off the harness. Once everything is grounded, it should all work correctly.

 

[Dean]

The white wire to the dome light sends a ground to the light so no the headlight switch does not make it hot.

Sounds like the headlight switch isn't grounded maybe.

 

[1Fast7D]

First- The dome light only works when the door is open. It will not operate when using the head lamp switch by twisting it. It's brand new.

Most likely headlamp switch not grounded as already stated.

I took a 12v tester and tested the white wire coming out of the head lamp switch and it's dead in all positions. This is where I need YOUR help to confirm that I think the BRAND NEW head lamp switch is bad.

You probably did this with the door open (and the dome light on). If so you wont have power as the circuit is already grounded. Test again, but this time with doors closed (or someone holding in door pin switches)

When I twist the knob all the way to make the dome light turn on, should i get power out of the white wire???

White wire will only have power when doors are closed. Twist the knob all the way GROUNDS the white wire making the dome lamp light.

The orange wire seems to always be HOT. I appreciate your help on this one.

Its supposed to be. The orange is power in from the parking lamp fuse. It only supplys power to the parking lamps, and dash lamps.

Second - (which may be related to the first) I have an HEI Distributor. My tach doesn't seem to work properly without the head lights being ON. When I turn the head lights off, the tach idles around 1k rpm and when I give it throttle it goes down to zero.

What is the voltage at battery with car running and headlights off?

 

[gonec0untry]

First - All grounds are connected to the carrier frame, except for the longer one which bolts to the brake release bracket. I've tested all the grounds with an Ohm meter and they all read 00.0 when attached. As far as I've learned that means it's a good ground. I even took out the dremmel (sp) tool and ground down to bare metal for ALL the grounds. (except the block and firewall to frame. I haven't done those yet. it's been raining)

The ground strap for the light switch is in the car and is screwed to the dash carrier as well. (same area as the other two grounds, but all have their own screw) I shall test the ground on the strap tonight.

So I take it that the White wire would NOT make the tester light up even if the switch is grounded properly? If it's NOT grounded properly would the dash lights even work? Cause the dash lights all work and the twist knob increase the strength of the light as it should. Only part that doesn't work is to turn on the dome light. I believe I did test this with the door closed, but I'll try again.

 

[Tom Mobley]

hook the test light to a 12V source and test the terminal the white wire goes to, see if it becomes a ground when the switch is turned to the left. The test light is reversible, works in either direction.

 

[Dean]

The white wire will show some voltage at point "A" when there is no ground but it will be in series with the bulb filament so the test light will be dim.

 

[gonec0untry]

hook the test light to a 12V source and test the terminal the white wire goes to, see if it becomes a ground when the switch is turned to the left. The test light is reversible, works in either direction.

That really confused me. You're saying to test the white wire at the dome light itself? I know the dome light works though. it lights up when the door opens.

 

[gonec0untry]

update! I tested the white wire with the door closed and the tester lights up in ALL positions of the switch. What does that mean?

Also, I tested the grounds with an ohm meter and they all read 00.0. I tested the metal casing of the head light switch and it read zero. I tested the strap down below where it screws to the carrier and it also read zero. I also tested the nut that screws into the head lamp switch to the side of the dash frame and it also read 0. Doesn't that mean that the switch is grounded????

Does that mean the switch is bad?

 

[1Fast7D]

That really confused me. You're saying to test the white wire at the dome light itself? I know the dome light works though. it lights up when the door opens.

I believe he meant to say to test at the headlight switch white wire terminal.

 

[1Fast7D]

update! I tested the white wire with the door closed and the tester lights up in ALL positions of the switch. What does that mean?

Also, I tested the grounds with an ohm meter and they all read 00.0. I tested the metal casing of the head light switch and it read zero. I tested the strap down below where it screws to the carrier and it also read zero. I also tested the nut that screws into the head lamp switch to the side of the dash frame and it also read 0. Doesn't that mean that the switch is grounded????

Does that mean the switch is bad?

I dont believe you are doing the tests correctly. Disconnect the wires from the headlight switch. Set you meter for ohms. Place one lead on the terminal the white wire goes to, the other on the grounding ring. With the knob twisted to make dome light come on, do you have continuity (00.0) between the two? Twist the knob to make dome light turn off, you should not have continuity between the two. This will at least tell you if its the headlight switch, or not.

 

[gonec0untry]

I dont believe you are doing the tests correctly. Disconnect the wires from the headlight switch. Set you meter for ohms. Place one lead on the terminal the white wire goes to, the other on the grounding ring. With the knob twisted to make dome light come on, do you have continuity (00.0) between the two? Twist the knob to make dome light turn off, you should not have continuity between the two. This will at least tell you if its the headlight switch, or not.

Thanks for responding Greg. When I test the switch tonight with the knob turned to the right to make the light turn off, should the reading be 00.0 or should it have any number higher than 00.0? thanks again!

Rich

 

[Dean]

With the wire disconnected from the switch and the knob in the "light off" position, there should be zero continuity from switch to ground.
With the wire disconnected from the switch and the knob in the "light on" position there should be infinity continuity from switch to ground.

 

[gonec0untry]

update:

Late last night I figured out I have the WRONG headlight switch. There is no terminal for the white wire. I put my old one back in (which I thought was bad) and everything worked. Well, almost everything. The copper on the CB broke right above the AMP gauge light socket. I read about a Curcuit writer pen I can get from Radio Shack to make that repair without pulling the dash back out. One thing though, when i touch the tip of my tester to complete the curcuit the only light that will light up is the one on the underside of the Tach. All the rest work as they should no matter. The AMP light has power on both sides. I don't think that's correct. It worked fine before I swaped switches, and before the break in the copper.

What would now cause the strip to have 12v on both sides of the bulb for the AMP gauge???

the Tach also still only works properly with the head lights on. I may have one of the ground wires attached in the wrong location. I have two ground wires next to where the strap is for the head light and the third down on the brake brake bracket. Which one should go on the steel gauge housing? the shortest one? Or does it matter which one?!? That may be why my Tach only works with the lights on. ??!???!??!!?

Thank you everyone for your help!!

 

[Kirby10]

With the wire disconnected from the switch and the knob in the "light on" position there should be infinity continuity from switch to ground.

I have never heard an electrical "short" called "infinity continuity"...

You might need to trademark that Dean or I'm going to start using that term around the R&D Lab.
.

 

[John D]

I have never heard an electrical "short" called "infinity continuity"...

You might need to trademark that Dean or I'm going to start using that term around the R&D Lab.

I was told by a Tech Support person to desolder the original value, then install "zero ohm" resistors in their place once.... (to convert the inputs on an audio mixer).

I said: "Do you mean a jumper?"
"NO, a zero ohm resistor"
"Oh, Ok - I'll have to order some then...."

 

[gonec0untry]

update: My Tachometer problems are solved!!!!!!!

I'm not sure if I mentioned this in a past update, but my car had a MSD coil in my HEI distributor. I put the old coil back in the car and the tach worked like a charm. Soooo Happy my Tach problems are over.

Now I have a reproduction Tach to sell cause I put an original tach in car thinking maybe the tach was bad. As it turns out, the repro tach is just fine!!!