Last week a friend who was working on his 1967 had two 1995131 Headlamp switches that didn't dim the cluster lamps, only full bright. We diagnosed the faults using his voltmeter, probing the switch terminals as I walked him through some tests by phone. Both rheostats were bad.
I had a old 1995149 Headlamp switch sitting on the shelf, along with many other old original switches that have been waiting for me to repair. I knew it had a bad rheostat, so I decided to experiment.
1203221742_resized.jpg
I took the 149 switch apart and saw it had a break in the rheostat close to the rivet where it terminates. All rheostats typically break in this area due to the arcing when coming off of the the rivet, which is the load from the lamps. As I recall, the rheostat wire is made of tungsten and difficult to repair. I used needle nose pliers and removed the broken piece and left a small piece still attached to the rivet.
Then I stretched to remaining wire over toward the rivet and the remaining wire. Using a high heat soldering iron, liquid flux, and silver solder, I was able to repair it. I gave it the tug test with a pick and it appeared strong. I later tested the repair electrically, using a 1967 Main harness loaded with dash bulbs. Results described later, along with some interesting observations.
So I attempted to also fix the two 131 switches using a similar repair method. Here are some photos of the repair sequence. I took photos this time. Note the photos may be from either switch, as evidenced by the two colors of the plastic actuator.
Using a flat blade screwdriver, lift the metal tabs away from the housing. Carefully lift the metal cover away from the housing.
After disassembly, you can see the rheostat wire broken close to the rivet. All switches usually have this fault. It was the weak link in the design. The heat generated nears 300*F when in it's lowest voltage setting, which is approximately 6 volts when fully dimmed, i.e. switch knob fully clockwise before the "off" position.
1204221248_resized.jpg
1204221248a_resized.jpg
After removing the short piece, I stretched the wire over to the remaining wire clamped by the rivet. Using the silver solder they were now reconnected. The rheostat resistance is approximately 6 ohms. The short piece I removed is negligible, likely a few hundred milliohms.
1204221302b_resized.jpg
1204221303_resized.jpg
I cleaned the rivets and verified good contact to the wire. If needed I could also solder the wire to the rivet. I actually repaired the 149 switch using that method.
The other 131 switch was taken apart further by the owner. I also soldered the backside of the rivets to the terminals.
1203221717_resized.jpg
I also soldered the terminals back to the contact plate within the switch housing after assembly as shown below.
1203221819_resized.jpg
I reassembled the switch after cleaning all contacts and using a silicone grease on the moving parts, note not on the contact points. The most difficult part of the process is keeping the contact block oriented properly. The end of the contact block with the hole for the knob shaft tip faces the knob. The o-ring is used to hold the contact block in place during reassembly.
1204221154_resized.jpg
The rheostat contactor wheel center hole mates only one way with the plastic actuator shaft. The spring attaches over the plastic actuator shaft first, then the wheel, ensuring the contactors face the rheostat. The spring keeps pressure on the contactor wheel to the rheostat.
1204221158_resized.jpg
1204221158a_resized.jpg
Note that earlier switches used a solid contactor wheel without the "fan" blades like on these later designs. Research explained the slotted fan blades were incorporated to help reduce heat, acting as a heat sink with multiple cooling features.
Here it is preassembled using the o-ring to hold the contactor assembly. Note the plate on top of the contactor(shown in a previous photo). A spring underneath it keeps it tensioned. The end of the plate has a keyhole which is used to capture the tip of the knob shaft. When the outer small button on the metal plate cover of the switch is pressed, it presses down on the plate/spring, lowering the plate to allow shaft removal.
1203221759_resized.jpg
Place the wheel/actuator assembly into the center hole in the rheostat porcelain and hold with one hand. Now the metal cover can be reinstalled with the other hand, simultaneously placing the front of the metal cover over the plastic actuator, then over the porcelain and down over the housing. At this point slide the o-ring away while keeping the assembly tight. Using a flat blade screwdriver, press the metal tabs of the cover back over the housing side keepers.
1204221202_resized.jpg
1203221818a_resized.jpg
So I had to test all 3 switches for functionality. I used a ohm meter to check all switch functions, including the dimming function. The rheostat measures around 5 ohms, rivet end to end of coil.
All tests passed. I then configured a main harness loaded with dash bulbs. I had to jumper each lamp socket ground as I didn't have a cluster. I left each switch in full dim mode for about 10 minutes. All 3 switches had fully functional rheostats again.
Note that to save the life of the rheostat, keep the lamps on bright. By design, this bypasses the rheostat from the circuit
Full Bright
1205221415_resized.jpg
Dimmed
1205221405_resized.jpg
Full Bright in darkspace
1205221414_resized.jpg
Dimmed in darkspace.
1205221415a_resized.jpg
Are you noticing that the lamps closest to the voltage source, left side, are brighter than those farther away at the clock area to the right?
I believe this is a artifact of the harness design. From the fuse panel, only one 18 Gauge Gray wire enters the harness and feeds all 14+ dash lamps. The furthest lamps get slightly lower voltage due to the voltage drops along the harness.
Another interesting measurement. Be very careful when putting hands up on a operating switch when in dimming mode. Also make sure all wires and loose items are far away from the switch.
The housing.....267*
1205221412_resized.jpg
The porcelain....279*. Note at one instant it read 288*.
1205221413_Burst01_resized.jpg
EDIT: 2/15/2024
NEVER USE ANY TYPE OF LUBRICANT, PARTICULARLY ANYTHING FLAMABLE, ON THE RHEOSTAT!!! IF IT SQUEAKS, IT'S NORMAL.
Notes:
The wheel contactor outer contact rivet is the source voltage from the fuse panel Tail lamps circuit. The wheel center contact goes to the lamps, via a fuse. This functions only when the knob is pulled in Park or Headlamp mode. Note that because of this design feature, if you ever notice dash lamps off, it could be the main fuse for the tail lamp circuit is blown, a dangerous driving condition.
Rotating knob positions are as follows:
Full CW - Dash lamps Off
In this position the rotating wheel outer contactor moves away from the rheostat wire on to the porcelain, opening the circuit.
Full CCW(before detent click) - Dash lamps Full bright
In this position the rotating wheel contactor moves away from the rheostat wire on to the rivet supplying max voltage to the lamps.
Full CCW(after detent click) - Dash lamps Full bright, Courtesy lamps On
In this position, as above, the dash lamps are still full bright, and a separate copper contactor is closed onto the switch metal cover, activated by the plastic actuator tab pushing down on the copper. This connects cluster ground to the separate courtesy lamp circuit, turning them on.
Partial rotation CW/CCW - Dash lamps Dimmed CW, Brighter CCW
The rheostat is in the circuit varying voltage to the lamps.
====
I had a old 1995149 Headlamp switch sitting on the shelf, along with many other old original switches that have been waiting for me to repair. I knew it had a bad rheostat, so I decided to experiment.
1203221742_resized.jpg
I took the 149 switch apart and saw it had a break in the rheostat close to the rivet where it terminates. All rheostats typically break in this area due to the arcing when coming off of the the rivet, which is the load from the lamps. As I recall, the rheostat wire is made of tungsten and difficult to repair. I used needle nose pliers and removed the broken piece and left a small piece still attached to the rivet.
Then I stretched to remaining wire over toward the rivet and the remaining wire. Using a high heat soldering iron, liquid flux, and silver solder, I was able to repair it. I gave it the tug test with a pick and it appeared strong. I later tested the repair electrically, using a 1967 Main harness loaded with dash bulbs. Results described later, along with some interesting observations.
So I attempted to also fix the two 131 switches using a similar repair method. Here are some photos of the repair sequence. I took photos this time. Note the photos may be from either switch, as evidenced by the two colors of the plastic actuator.
Using a flat blade screwdriver, lift the metal tabs away from the housing. Carefully lift the metal cover away from the housing.
After disassembly, you can see the rheostat wire broken close to the rivet. All switches usually have this fault. It was the weak link in the design. The heat generated nears 300*F when in it's lowest voltage setting, which is approximately 6 volts when fully dimmed, i.e. switch knob fully clockwise before the "off" position.
1204221248_resized.jpg
1204221248a_resized.jpg
After removing the short piece, I stretched the wire over to the remaining wire clamped by the rivet. Using the silver solder they were now reconnected. The rheostat resistance is approximately 6 ohms. The short piece I removed is negligible, likely a few hundred milliohms.
1204221302b_resized.jpg
1204221303_resized.jpg
I cleaned the rivets and verified good contact to the wire. If needed I could also solder the wire to the rivet. I actually repaired the 149 switch using that method.
The other 131 switch was taken apart further by the owner. I also soldered the backside of the rivets to the terminals.
1203221717_resized.jpg
I also soldered the terminals back to the contact plate within the switch housing after assembly as shown below.
1203221819_resized.jpg
I reassembled the switch after cleaning all contacts and using a silicone grease on the moving parts, note not on the contact points. The most difficult part of the process is keeping the contact block oriented properly. The end of the contact block with the hole for the knob shaft tip faces the knob. The o-ring is used to hold the contact block in place during reassembly.
1204221154_resized.jpg
The rheostat contactor wheel center hole mates only one way with the plastic actuator shaft. The spring attaches over the plastic actuator shaft first, then the wheel, ensuring the contactors face the rheostat. The spring keeps pressure on the contactor wheel to the rheostat.
1204221158_resized.jpg
1204221158a_resized.jpg
Note that earlier switches used a solid contactor wheel without the "fan" blades like on these later designs. Research explained the slotted fan blades were incorporated to help reduce heat, acting as a heat sink with multiple cooling features.
Here it is preassembled using the o-ring to hold the contactor assembly. Note the plate on top of the contactor(shown in a previous photo). A spring underneath it keeps it tensioned. The end of the plate has a keyhole which is used to capture the tip of the knob shaft. When the outer small button on the metal plate cover of the switch is pressed, it presses down on the plate/spring, lowering the plate to allow shaft removal.
1203221759_resized.jpg
Place the wheel/actuator assembly into the center hole in the rheostat porcelain and hold with one hand. Now the metal cover can be reinstalled with the other hand, simultaneously placing the front of the metal cover over the plastic actuator, then over the porcelain and down over the housing. At this point slide the o-ring away while keeping the assembly tight. Using a flat blade screwdriver, press the metal tabs of the cover back over the housing side keepers.
1204221202_resized.jpg
1203221818a_resized.jpg
So I had to test all 3 switches for functionality. I used a ohm meter to check all switch functions, including the dimming function. The rheostat measures around 5 ohms, rivet end to end of coil.
All tests passed. I then configured a main harness loaded with dash bulbs. I had to jumper each lamp socket ground as I didn't have a cluster. I left each switch in full dim mode for about 10 minutes. All 3 switches had fully functional rheostats again.
Note that to save the life of the rheostat, keep the lamps on bright. By design, this bypasses the rheostat from the circuit
Full Bright
1205221415_resized.jpg
Dimmed
1205221405_resized.jpg
Full Bright in darkspace
1205221414_resized.jpg
Dimmed in darkspace.
1205221415a_resized.jpg
Are you noticing that the lamps closest to the voltage source, left side, are brighter than those farther away at the clock area to the right?
I believe this is a artifact of the harness design. From the fuse panel, only one 18 Gauge Gray wire enters the harness and feeds all 14+ dash lamps. The furthest lamps get slightly lower voltage due to the voltage drops along the harness.
Another interesting measurement. Be very careful when putting hands up on a operating switch when in dimming mode. Also make sure all wires and loose items are far away from the switch.
The housing.....267*
1205221412_resized.jpg
The porcelain....279*. Note at one instant it read 288*.
1205221413_Burst01_resized.jpg
EDIT: 2/15/2024
NEVER USE ANY TYPE OF LUBRICANT, PARTICULARLY ANYTHING FLAMABLE, ON THE RHEOSTAT!!! IF IT SQUEAKS, IT'S NORMAL.
Notes:
The wheel contactor outer contact rivet is the source voltage from the fuse panel Tail lamps circuit. The wheel center contact goes to the lamps, via a fuse. This functions only when the knob is pulled in Park or Headlamp mode. Note that because of this design feature, if you ever notice dash lamps off, it could be the main fuse for the tail lamp circuit is blown, a dangerous driving condition.
Rotating knob positions are as follows:
Full CW - Dash lamps Off
In this position the rotating wheel outer contactor moves away from the rheostat wire on to the porcelain, opening the circuit.
Full CCW(before detent click) - Dash lamps Full bright
In this position the rotating wheel contactor moves away from the rheostat wire on to the rivet supplying max voltage to the lamps.
Full CCW(after detent click) - Dash lamps Full bright, Courtesy lamps On
In this position, as above, the dash lamps are still full bright, and a separate copper contactor is closed onto the switch metal cover, activated by the plastic actuator tab pushing down on the copper. This connects cluster ground to the separate courtesy lamp circuit, turning them on.
Partial rotation CW/CCW - Dash lamps Dimmed CW, Brighter CCW
The rheostat is in the circuit varying voltage to the lamps.
====
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