Low Beam Relay Not Functioning

[utee05]

Hi All,
I installed relays in my '72 GMC. I followed the diagram below:


As a note I am using H4 headlights for my low beams. Standard H1 sealed bulbs for my high beams.

When I hit my switch the high beams work, which in turn means all 4 of my lights are on. When I hit the dimmer switch nothing turns on. I know the relays are getting 12V from the battery. I used a 30 amp breaker fuse in between the power from the relay to the battery. I know ground is good. I used the light green and tan wires that were running along the driver side underneath the hood and used those to connect to the relay as stated in the wiring diagram.

Could I possibly have a bad relay? I know the lights work cause they all turn on and the dimmer switch is new. Is there some fuse I need to worry about that could be causing the low beams not to work?

[DesertCat]

if you wired it exactly like the drawing, and all 4 bulbs are lit when dimmer is in high... the either the dimmer is bad or somehow you miswired at the dimmer.

[VetteVet]

Swap the two relay wires at 85 and if the highs light and the lows don't then you have a bad relay., or the power from the relay at 87 is not getting to the low beams.
This test will also verify that the dimmer is Ok because it means that both wires off the dimmer are getting voltage to both relays.

If the situation reverses then it means that the dimmer switch or wire on the low beam side is not getting power out to the relay.

You can check for power at 87 and tell if the relays are working as well,

[DesertCat]

Originally Posted by VetteVet

Swap the two relay wires at 85 and if the highs light and the lows don't then you have a bad relay., or the power from the relay at 87 is not getting to the low beams.
This test will also verify that the dimmer is Ok because it means that both wires off the dimmer are getting voltage to both relays.

If the situation reverses then it means that the dimmer switch or wire on the low beam side is not getting power out to the relay.

You can check for power at 87 and tell if the relays are working as well,

Sorry VetteVet, but that is confusing it... if as he states, all 4 bulbs light when the dimmer is switched to high beam, it simply cannot be anything but the dimmer.

If that is not the case, and the low beams never come on regardless of switch position/condition, then you would be correct. It would be far easier and quicker to swap relays though... if the problem reverses then it is a bad relay, if not then check for main power at relay (30), switch power (85) then if those check out, make sure you have continuity from output (87) to the light sockets. Finally, don't forget the relay and bulbs also need a good ground, so check (86) and the bulb sockets are grounded.

The OP needs to clarify what exactly he means by "which in turn means all 4 of my lights are on" Does that mean all 4 light truly do come on, or merely should come on?

[FLEET72]

Originally Posted by DesertCat

Sorry VetteVet, but that is confusing it... if as he states, all 4 bulbs light when the dimmer is switched to high beam, it simply cannot be anything but the dimmer.

If that is not the case, and the low beams never come on regardless of switch position/condition, then you would be correct. It would be far easier and quicker to swap relays though... if the problem reverses then it is a bad relay, if not then check for main power at relay (30), switch power (85) then if those check out, make sure you have continuity from output (87) to the light sockets. Finally, don't forget the relay and bulbs also need a good ground, so check (86) and the bulb sockets are grounded.

The OP needs to clarify what exactly he means by "which in turn means all 4 of my lights are on" Does that mean all 4 light truly do come on, or merely should come on?

Here are some visual representations to help in understanding whats going on. I didn't make one showing power not getting to the low beam relay at terminal 85, I would start looking for voltage there.

High Beam, four lights on:


Low Beam, Good Dimmer, Bad Relay:


Low Beam, Good Dimmer, Good Relay, Bad Connection: (the bad connection could be anywhere between the relay and the lamps.)


Low Beam, All Good: (this is what we want!)

[VetteVet]

.....

Originally Posted by DesertCat

Sorry VetteVet, but that is confusing it... if as he states, all 4 bulbs light when the dimmer is switched to high beam, it simply cannot be anything but the dimmer. Not really! If you read the very first sentence and look at the diagram, it's a GMC and all four lights are supposed to come on, on high beams also the diagrams show the green feed wires going to all four lights from the high beam relay.


If that is not the case, and the low beams never come on regardless of switch position/condition, then you would be correct. That's how I read his post.

It would be far easier and quicker to swap relays though...That's what you are doing when you change the tan and green wires to the 85 terminal on the relays.

if the problem reverses then it is a bad relay, It just confirms that the dimmer is good, and the tan wire has power to the relays. if not then check for main power at relay (30), switch power (85) then if those check out, make sure you have continuity from output (87) to the light sockets. Finally, don't forget the relay and bulbs also need a good ground, so check (86) and the bulb sockets are grounded.

All four bulbs come on so sockets are good and grounds are good. The outside lights are dual element so It's possible that the low beam terminals might be bad but they would both have to be bad for both lights to not come on.
It's also possible that both low beam elements are burnt out

The OP needs to clarify what exactly he means by "which in turn means all 4 of my lights are on" Does that mean all 4 light truly do come on, or merely should come on? Unless I read it wrong he said they all come on.

[utee05]

All 4 headlights come on when the dimmer switch is set to high beams. Should this not be the case cause H4 bulbs are both high/low bulbs? When the dimmer switch is set to low beams nothing comes on.

My original dimmer switch went out a couple of weeks ago (before relay conversion) so I just got a new dimmer switch. I would hope that the dimmer switch I just bought is good. I know my original dimmer switch is bad cause when I hook it back up all I hear are clicking noises coming from the fuse panel area and no lights turn on at all.

I have checked each terminal 30 on both relays and see that voltage is getting to each one. When the dimmer switch is set to High beam I see the switch power (85) on the High beam relay getting full voltage along with (87) get the same voltage.

Also my grounds are good on both relays. When the switch is set to high beams I checked the relay on the low beams and I do not see much power out of terminal 85 & 87. What should be the voltage at these terminals on the low beam relay when the dimmer switch is set to high beams?

[VetteVet]

Originally Posted by utee05

All 4 headlights come on when the dimmer switch is set to high beams. Should this not be the case cause H4 bulbs are both high/low bulbs? When the dimmer switch is set to low beams nothing comes on.

My original dimmer switch went out a couple of weeks ago (before relay conversion) so I just got a new dimmer switch. I would hope that the dimmer switch I just bought is good. I know my original dimmer switch is bad cause when I hook it back up all I hear are clicking noises coming from the fuse panel area and no lights turn on at all.

I have checked each terminal 30 on both relays and see that voltage is getting to each one. When the dimmer switch is set to High beam I see the switch power (85) on the High beam relay getting full voltage along with (87) get the same voltage.

85 turns on the relay so 87 gets voltage from 30. The same should happen at the low beam relay. Like I said, switch the wires that go to 85 from the dimmer switch and see if the lows come on. If they don't then the relay or the wiring from 87 to the low beam terminal on the light is not getting power to the light. Make sure that the low beams come on by connecting the wire at 30 to the wire at 87 with a short jumper. That's all the relay is doing.

Also my grounds are good on both relays. When the switch is set to high beams I checked the relay on the low beams and I do not see much power out of terminal 85 & 87. What should be the voltage at these terminals on the low beam relay when the dimmer switch is set to high beams?

That is correct there should be no power on the low beam relay when high beam is selected and vice versa except for terminal 30.

[utee05]

Thanks for confirmation. I'll check out everything tonight when I get home. I'll also pick up another relay just in case that is the issue.

I do remember when first wired the relays the low beams would turn on when the dimmer switch was set to low beam. Not sure if something in the wiring got loose or relay died but I do recall them working at one point.

Thanks for all of the help and I'll have an update later on.

[DesertCat]

Originally Posted by VetteVet

.....

I did not see the fact that you pointed out that the high beam relay fed all 4 bulbs, that changes everything.

Thought it was energizing both relays for high beam operation, and if it had, I would have been correct. but... sadly, I have to admit that I was wrong.

Dang, that's twice this year

[utee05]

Originally Posted by DesertCat

I did not see the fact that you pointed out that the high beam relay fed all 4 bulbs, that changes everything.

Thought it was energizing both relays for high beam operation, and if it had, I would have been correct. but... sadly, I have to admit that I was wrong.

Dang, that's twice this year

Not bad, only twice this year. I've already been wrong twice this week

[VetteVet]

Think nothing of it . I posted that at 1:30 in the morning so I probably was half asleep. One thing I keep forgetting is that I have to be careful with my answers and not get too technical because not everybody understands the electrics on these old trucks. I would never take offense if some one thought I had given bad info. I always try to give reliable advice but sometimes I make mistakes too.

[DesertCat]

Originally Posted by VetteVet

Think nothing of it . I posted that at 1:30 in the morning so I probably was half asleep. One thing I keep forgetting is that I have to be careful with my answers and not get too technical because not everybody understands the electrics on these old trucks. I would never take offense if some one thought I had given bad info. I always try to give reliable advice but sometimes I make mistakes too.

Thanks, all my pencils have erasers... for a reason

I was up way too late myself... work the zombie shift here on the other side of the planet, 84 hour weeks, not much sleep.

Woke up today from an earthquake, was dreaming it was my wife nudging me to stop snoring then, unfortunately, reality. Oh, I'm in Afghanistan

[VetteVet]

Originally Posted by DesertCat

Thanks, all my pencils have erasers... for a reason

I was up way too late myself... work the zombie shift here on the other side of the planet, 84 hour weeks, not much sleep.

Woke up today from an earthquake, was dreaming it was my wife nudging me to stop snoring then, unfortunately, reality. Oh, I'm in Afghanistan

Thank you for your service stay safe. I was in Kuwait for Iraqi Freedom supporting the Army and Marines with that awesome machine known as the A-10 Warthog.

[FLEET72]

Originally Posted by DesertCat

Oh, I'm in Afghanistan

Originally Posted by VetteVet

Thank you for your service stay safe. I was in Kuwait for Iraqi Freedom supporting the Army and Marines with that awesome machine known as the A-10 Warthog.

+1! To both of you!

[utee05]

Did a quick check this morning and determined that my relays are not bad. I swapped out the wiring between the low and high beams and it still worked as before. So this means my relays aren't bad and I suspect something in my wiring is jacked up. I'll be working on that this weekend and hopefully that will fix things.

I am ruling out the dimmer switch as I just bought this part, but who knows. After I check and fix my wiring then I'll know for sure it that was the cause or it was the dimmer switch. Baby steps.

[DesertCat]

Thanks for the kind words guys!

utee05, Which wiring exactly did you swap?
As far as the dimmer, yes, you can get a bad new one. Unlikely but possible.

Do you have a voltmeter? Would save you a ton of time troubleshooting your problem.

When I was a kid and didn't have any money I used a cut off side marker light socket/bulb for a 12v tester. Actually, used that for years... one end to a ground and jam the other to what I was testing - worked great

[utee05]

All I did was I swapped the wires of the high beams into the other relay that was being used for the low beams just to check if the relay was bad or not. Since everything still functioned this means the relays aren't bad.

I think there may be some loose wiring when I made connections for the low beams so I'll need to check on that.

I do have a multimeter and that was what I was using to verify that the relays were getting power and had a good ground.

How would I check the dimmer switch?

[FLEET72]

Originally Posted by utee05

How would I check the dimmer switch?

Since you know that the high beam works (green wire). Check for 12V at the brown wire after switching to low.

[utee05]

Thanks. I'll do some checks either tonight or over the weekend.

[DesertCat]

Originally Posted by utee05

Thanks. I'll do some checks either tonight or over the weekend.

Well, hurry up! We're waiting!

[utee05]

Well I finally got some time this afternoon to check the wiring. When switched to low I saw voltage coming out of the switch. I also verified this on the wire that was going to the relay on terminal 85. I checked the voltage coming out of terminal 87 and I did not get any voltage at all. Does this mean the relay is bad?

I swapped out the relays (again) from the high beam to the low beam and still the same thing (low beams not working). Is there something that I am missing? Is there a fuse that controls the lights that may have blown?

[utee05]

I tried out something in checking my wires. I left terminal 87 connected to the high beam wire but connected terminal 85 coming from the low beam switch wire. I then toggled the dimmer switch to high beams and noticed only the driver side lights turned on (both high/low beams). Not sure what this proves but found it interesting.

[VetteVet]

Originally Posted by utee05

I tried out something in checking my wires. I left terminal 87 connected to the high beam wire but connected terminal 85 coming from the low beam switch wire. I then toggled the dimmer switch to high beams and noticed only the driver side lights turned on (both high/low beams). Not sure what this proves but found it interesting.

It sounds to me like you need to double check the wiring from your relays to your lights. If you look at the diagram below you will see that the high beam relay will light all four lights and the low beam relay only lights the two outside ones.

[utee05]

I am not sure what else I need to check. When I have everything as wired in the diagram you attached the low beams do not turn on when the dimmer switch is set to low beam. When I set the dimmer switch to high beam all 4 turn on. I have verified the dimmer switch works cause I see 12V on the tan wire.

The experiment I did was just to see what happens when I mess with my wiring. I was just trying things out.