No headlights

[87ChevyR10]

Ok, so my headlights decided to quit working at the most inappropriate time: after work, in the dark with buckets of rain!

Every other light source works: turn signals, brake lights, parking lamps, dome light and dash lights. One of my co-workers said he saw them flicker on then off again. They worked the previous night. Ended up jury rigging the headlights to the battery until I got home.

I won't be able to check further into this until later today when it quits raining. So, I really only have two places to check: the dimmer switch and the fuse link for the headlights. I'm hoping it's just the switch.

Anyone have any thoughts about this?

 

[87ChevyR10]

Well, headlights work again. Truck had been sitting outside when all the rain and wind hit yesterday. So, I don't know where to begin now.

Ideas?

 

[smoothandlow84]

Short in the headlight socket ??. Pull off the electrical socket, apply some dielectric grease and reinstall. It sounds like water found its way into the socket causing a short.

 

[87ChevyR10]

Short in the headlight socket ??. Pull off the electrical socket, apply some dielectric grease and reinstall. It sounds like water found its way into the socket causing a short.

Good idea! I'll get some today. Thx!

 

[87ChevyR10]

Short in the headlight socket ??. Pull off the electrical socket, apply some dielectric grease and reinstall. It sounds like water found its way into the socket causing a short.

I got to thinking about this more. If water was shorting out the sockets, why would hooking them directly to the battery get them working again?

 

[chengny]

The headlight switch itself bad? Or maybe that internal breaker is failing. Do you have any add-on loads connected to the headlight circuit?

It's true that all of the other (5) lighting circuits you mention as working are fed by the same fusible link as the headlights. But only the power for the high/low beams is run directly to the H/L switch.

Two of them - the combined brake/directional lighting circuits - never even go near the headlight switch. Forget about those.


After leaving the link, the other 3 circuits (park/tail, instrument & courtesy/dome) first go into the fuse block and connect to their dedicated fuses. Next, after exiting the fuse block, they continue on to their control switches and finally to the lights associated with the circuit.

What confuses the situation sometimes is that the controls for the other 3 circuits you mention (tail/parking lights, dome/courtesy lighting and the dash lighting) are incorporated into the headlight switch. But they are in no way cross-connected to the H/L circuit. Within the switch, each circuit has it's own dedicated set of contacts.

The fact that all those other lighting circuits are working would confirm that the link is good and so power should be available to the H/L switch on the big red lead. Remember that lead only supplies the H & L beams - nothing else. Power comes in on terminal 2, passes through the internal breaker, the closed switch contacts and then exits on terminal 10.


Also, I don’t know where (i.e. how far down the line from the bulkhead connection block) you made the emergency connection from the battery into the H/L feed. But if the H/L's worked - and didn’t melt your jumper wire – that would indicate that all is well from the dimmer to the lamps.

A quick diagnostic for the two switches and associated (in cab) wiring:


1. Check for power at the big red wire where it enters the H/L switch at terminal #2. If there is no power there – and you do have power on the load side of the fusible link – that would indicate that the red feed wire to the headlights is broken somewhere between the link and the switch.

2. If you find that there is 12 VDC available on the red lead as it enters the switch, check for continuity through the switch. Pull the switch all the way out and confirm whether there is 12 VDC on the yellow lead where it connects to terminal # 10.

3. If there is no power at terminal 10 , the switch is failed/failing - or the internal circuit breaker is open. The circuit breaker is not serviceable, so either way it’s time for a new switch.

4. If there is power coming out of the switch at terminal 10, check the yellow lead for continuity over to the dimmer switch. Leave the switch pulled out and test for voltage on the yellow where it enters the dimmer on terminal 10.

5. No power in on the yellow? Indicates a broken feed to the dimmer from the H/L switch.

6. If you find power available into the dimmer on the yellow at 10, check the switch. Pick either H/L beams – you won’t know which unless the switch is working on the highs and power is available on the LT GRN lead.

7. Cycle the dimmer and note whether there is power coming out on the light green (highs) the tan (lows) or neither.

A simple wiring diagram for the headlight and dimmer switches:

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[87ChevyR10]

The headlight switch itself bad? Or maybe that internal breaker is failing. Do you have any add-on loads connected to the headlight circuit?

It's true that all of the other (5) lighting circuits you mention as working are fed by the same fusible link as the headlights. But only the power for the high/low beams is run directly to the H/L switch.

Two of them - the combined brake/directional lighting circuits - never even go near the headlight switch. Forget about those.


After leaving the link, the other 3 circuits (park/tail, instrument & courtesy/dome) first go into the fuse block and connect to their dedicated fuses. Next, after exiting the fuse block, they continue on to their control switches and finally to the lights associated with the circuit.

What confuses the situation sometimes is that the controls for the other 3 circuits you mention (tail/parking lights, dome/courtesy lighting and the dash lighting) are incorporated into the headlight switch. But they are in no way cross-connected to the H/L circuit. Within the switch, each circuit has it's own dedicated set of contacts.

The fact that all those other lighting circuits are working would confirm that the link is good and so power should be available to the H/L switch on the big red lead. Remember that lead only supplies the H & L beams - nothing else. Power comes in on terminal 2, passes through the internal breaker, the closed switch contacts and then exits on terminal 10.


Also, I don’t know where (i.e. how far down the line from the bulkhead connection block) you made the emergency connection from the battery into the H/L feed. But if the H/L's worked - and didn’t melt your jumper wire – that would indicate that all is well from the dimmer to the lamps.

A quick diagnostic for the two switches and associated (in cab) wiring:


1. Check for power at the big red wire where it enters the H/L switch at terminal #2. If there is no power there – and you do have power on the load side of the fusible link – that would indicate that the red feed wire to the headlights is broken somewhere between the link and the switch.

2. If you find that there is 12 VDC available on the red lead as it enters the switch, check for continuity through the switch. Pull the switch all the way out and confirm whether there is 12 VDC on the yellow lead where it connects to terminal # 10.

3. If there is no power at terminal 10 , the switch is failed/failing - or the internal circuit breaker is open. The circuit breaker is not serviceable, so either way it’s time for a new switch.

4. If there is power coming out of the switch at terminal 10, check the yellow lead for continuity over to the dimmer switch. Leave the switch pulled out and test for voltage on the yellow where it enters the dimmer on terminal 10.

5. No power in on the yellow? Indicates a broken feed to the dimmer from the H/L switch.

6. If you find power available into the dimmer on the yellow at 10, check the switch. Pick either H/L beams – you won’t know which unless the switch is working on the highs and power is available on the LT GRN lead.

7. Cycle the dimmer and note whether there is power coming out on the light green (highs) the tan (lows) or neither.

A simple wiring diagram for the headlight and dimmer switches:

You must be registered for see images attach

Only extra load on the HL circuit was the light for the aftermarket tach. Nothing else. IMO, I'm gonna guess the HL switch is going bad. If there were broken connections, I would notice flickering lights when hitting bumps in the road.

The jury rig came straight from the battery directly to the HL sockets. The wire was warm, but not too hot to touch. The wire used was similar in size to the factory wiring. Heck, the HL's themselves were a bit brighter hooked up this way.

The only other issue I've had with the headlights is them sometimes shutting off when switching from low to high and high to low. That switch is fairly new. Also, the lower HL pair have never worked since I got the truck 3 years ago.

I didn't get to checking anything out today. Hopefully tomorrow.

 

[Camar068]

The only other issue I've had with the headlights is them sometimes shutting off when switching from low to high and high to low. That switch is fairly new. Also, the lower HL pair have never worked since I got the truck 3 years ago.

I didn't get to checking anything out today. Hopefully tomorrow.

Hate to say but it sounds like the hi-low switch. Did they shut off when switching H-L prior to replacing it? If it didn't, that may be the culprit. It may have finally just crapped out.

Just a thought.

 

[87ChevyR10]

Hate to say but it sounds like the hi-low switch. Did they shut off when switching H-L prior to replacing it? If it didn't, that may be the culprit. It may have finally just crapped out.

Just a thought.

Yeah, they did, hence why I installed a new one.

 

[Camar068]

ah missed that part, sorry. Knew you replaced it but not when.

 

[Camar068]

On mine, if the ground wire on the passenger side isn't hooked to chassis, that side won't work.

 

[87ChevyR10]

Got the new HL/dimmer (on dash, not column) switch installed today. I still lose headlights when switching low to hi on occasion.

 

[87ChevyR10]

So, what would cause intermittent loss of headlights when switching low to hi? The hi/low switch I replaced did the same thing. After switching several times, the headlights finally stay on and switch like they are supposed to. I still don't get anything from the lower pair, though.

 

[chengny]

What you'll have to do is catch it in the act and pull over. Then quickly (while the lights are still out) grab your meter/test probe and determine at which point in the circuit the open exists.

Since all the fused circuits - -that share a power supply with the headlights - are functional and haven't exhibited any intermittent loss of power, you can skip over the fusible link. And that's good news because there is only one fusible link for that power feed into the cab. It is one the two links way down on the starter end of the cables.

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The single cable splits into two right at the bulkhead connection on the cab side of the firewall. That's directly behind the fuse block. To access that splice, you'd have to release the block from the firewall:

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I'd go right to the 2 terminal on the H/L switch for the first voltage check. The harness plug for the headlight switch has nice roomy bays for each of the leads:

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You can easily stick your meter/test light probe in and make contact with the copper terminal connector - without pulling the plug. That isn't an issue when checking the power coming in on the red. But when you go to verify the headlight switch is good, it's much easier to leave the plug on the switch and just check for voltage on terminal 10 - rather than checking continuity.



As far as the failure of the lower sealed beams to illuminate. If your 87 truck has quad headlights, this is how they should look on low beams:

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and on highs they should look like this:

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But, while you say that the dual filament upper lamps are working as designed, I'll bet they are not.

Look closely at the text that accompanies the two images showing high/low beam configuration. It describes which filaments in which lamps are energized for both modes of operation. Note that the upper sealed beam has two filaments of different wattage ratings. The most common combination is a 60 watt and a 40 watt filament. Conventional wisdom would seem to dictate that - when the high beams are selected, the filament with the higher wattage rating would be the one that is illuminated. It isn't that way however.

With the headlights on normal/low beams, there is no power supplied to the single 50 watt filament in the lower lamp. And in the dual filament upper lamp, when on low beams, power is applied to the filament with the higher wattage rating.

When the dimmer is switched to high beams, power is supplied to the single filament in the lower lamps. And in the upper lamps, when highs are selected, the higher wattage filament is de-energized and power is applied to the lower wattage filament.

So, if only your upper sealed beams are illuminating at all and you are seeing an increase in lighting intensity when the highs are selected (and the little blue light comes on), something is wrong in the circuitry.

Also, make sure the proper sealed beams are installed (i.e that they are compatible with the headlight wiring and terminal plugs). Provided that no modifications have been made, the correct sealed beams for your truck are the A1 style. The upper lamps are 2A1 and the lowers are 1A1:

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The A1 style sealed beams mainly differ from the B,C & D styles in the way the wiring is connected and the geometry of the terminal layout. The terminals on B,C & D lamps are layed out like an upright triangle. Looking from the back, the terminal assignments are: ground on the lower left, low beam on the top and the high beam on the lower right:

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The terminal geometry on an A1 style sealed beams looks like an inverted triangle with a 45 degree tilt to the left. From the back, the ground is on the upper left, low beam is on the upper right and the high beam lead connects at the bottom terminal:

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The A series is easy to identify due to the 45 degree bias of the terminal geometry:

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Even with the harness plugs attached:

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[87ChevyR10]

Thanks for the info, Chengy!

I can confirm all 4 HL's are the A1 style. What I can't tell you is if the lower pair are even good. Having functional hi-beams isn't much of a priority since I live in town; but that doesn't mean I don't want them working.

I'll try to get around checking voltages tomorrow if I can get the HL's to shut off while cycling the hi/low switch.

EDIT: "So, if only your upper sealed beams are illuminating at all and you are seeing an increase in lighting intensity when the highs are selected (and the little blue light comes on), something is wrong in the circuitry."

This statement just sunk in. This is exactly how my uppers work. I get a weaker beam on lows and a stronger beam on high and the blue dash light turns on. So technically, until I resolve the lowers, I should have my highs on because that is normal operation for the uppers on low beam setting. Wow, learn something new every day!

So, is it possible the plug for the hi/low switch to be installed up side down? <- Nevermind this question. It would be impossible to install the plug wrong. I wonder then if one of the pins isn't seating correctly.