Originally Posted by VetteVet (Post 5481608)

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,

Originally Posted by DesertCat (Post 5481651)

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?

Originally Posted by DesertCat (Post 5481651)

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.

Originally Posted by utee05 (Post 5481875)

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?

Originally Posted by VetteVet (Post 5481794)

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Originally Posted by DesertCat (Post 5482018)

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 :rolleyes:

:haha:

Originally Posted by VetteVet (Post 5482125)

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.

Originally Posted by DesertCat (Post 5482161)

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

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 :lol: then, unfortunately, reality. Oh, I'm in Afghanistan :(

Originally Posted by DesertCat (Post 5482161)

Oh, I'm in Afghanistan :(

Originally Posted by VetteVet (Post 5482300)

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.

Originally Posted by utee05 (Post 5484274)

How would I check the dimmer switch?

Originally Posted by utee05 (Post 5484354)

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

Originally Posted by utee05 (Post 5505648)

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.