69 Lighting Switch

[Pat K.]

Thanks,

Pat

[Peter L.]

Re: 69 Lighting Switch

Pat - Check the metal piece of the switch and see if it has a 3 digit number stamped on it. Older Delco-Remy switches had the last 3 digits of the part number stamped into the metal, later Delco replacement might have an ink stamp. That will help in knowing if it's either the original switch or an original part number replacement or some other replacement switch that could be configured differently from the original part. Pete

[Jack H.]

Re: 69 Lighting Switch

Not necessarily a short in that area... The HL switch has a potentiameter for adjusting the intensity of dash lamps. Should one of the lamps 'downstream' from the HL switch short (or the insulation on its power wire short), the HL switch is going to deliver more current than it was designed to handle.

The pot is metal in a ceramic surround that's connected to a Bakelite switch body. The path for heat to escape is primarily back down the electrical contacts with the 'weak' point being the ohmic contact surfaces of the HL switch's wiring harness connector. I think that's what you're seeing. Plastic surrounding the lead wire contacts that discolored due to localized heating...

Designing these circuits is always a challenge. You've got a plurality of downstream lamps drawing current on a single branch. Where do you set the branch circuit's fuse value? Do you want to lose ALL the lamps if just one malfunctions?

Bottom line, you can wind up with a 'race' condition... Who goes first...the branch circuit fuse or the potentiameter in the HL switch? That's one of the reasons used original HL switches are often A-OK except for the integrity of the resistance winding in the dimmer pot portion of the HL switch!

[Pat K.]

Re: 69 Lighting Switch

Pat - Check the metal piece of the switch and see if it has a 3 digit number stamped on it. Older Delco-Remy switches had the last 3 digits of the part number stamped into the metal, later Delco replacement might have an ink stamp. That will help in knowing if it's either the original switch or an original part number replacement or some other replacement switch that could be configured differently from the original part. Pete

Pete - 191 stamped into the metal and Delco Remy on the plastic. Pat

[Pat K.]

Re: 69 Lighting Switch

Not necessarily a short in that area... The HL switch has a potentiameter for adjusting the intensity of dash lamps. Should one of the lamps 'downstream' from the HL switch short (or the insulation on its power wire short), the HL switch is going to deliver more current than it was designed to handle.

The pot is metal in a ceramic surround that's connected to a Bakelite switch body. The path for heat to escape is primarily back down the electrical contacts with the 'weak' point being the ohmic contact surfaces of the HL switch's wiring harness connector. I think that's what you're seeing. Plastic surrounding the lead wire contacts that discolored due to localized heating...

Designing these circuits is always a challenge. You've got a plurality of downstream lamps drawing current on a single branch. Where do you set the branch circuit's fuse value? Do you want to lose ALL the lamps if just one malfunctions?

Bottom line, you can wind up with a 'race' condition... Who goes first...the branch circuit fuse or the potentiameter in the HL switch? That's one of the reasons used original HL switches are often A-OK except for the integrity of the resistance winding in the dimmer pot portion of the HL switch!

Jack - insightful information, thanks. But do you know if the one contact on the switch that's not connected to anything came from GM that way? I was looking at the wiring diagram and it looks like no wires are connected to that one, but those wiring diagrams can make my head spin sometimes.

Pat

[Greg L.]

Re: 69 Lighting Switch

Jack - insightful information, thanks. But do you know if the one contact on the switch that's not connected to anything came from GM that way? I was looking at the wiring diagram and it looks like no wires are connected to that one, but those wiring diagrams can make my head spin sometimes.

Pat

Yes Pat that's exactly how it came from GM. I also noticed this on my 69 a few days ago as I was putting the dash back together. It still has the original switch and harness and I also verified the "extra" terminal as not being used in the wiring diagram.

You're good to go!

[Pat K.]

Re: 69 Lighting Switch

ALCON - thank you for the information.

[Jack H.]

Re: 69 Lighting Switch

"But do you know if the one contact on the switch that's not connected to anything came from GM that way?"

Yes, it's part of the switch assy. That lead serves to hold the front ceramic dimmer assy to the plastic switch body until the top cover is installed and crimped in place. Plus, look at the switch more closely and you'll see its function...

The terminal connect through the ceramic to exit on the opposite side to the pot's rotation follower arm. When the dimmer is rotated all the way to one end of the illumination scale it 'clicks' home to give tactitle feedback that you've hit the end of the range.

At this point, the rotation follower arm rides UP on a cam to make contact with the metal switch cover which completes the terminal's circuit path to ground. Have you never noticed that the switch turns on the car's interior lamps at one end of dimmer rotation sweep?

[Jon S.]

Re: 69 Lighting Switch

For what it's worth, make sure all your light functions work properly before you button it all back up. On my '69 I could not figure out why the dash lights would not dim and were always at high intensity. Turns out someone had moved one of the connectors in the harness plug to that 'empty' socket. That one cost me about 3 different h/l switches and I don't know how many hours of frustration befor I figured out the problem.