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NCOR
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8,449 Posts
Discussion Starter #1
So my truck hates me. Ive had an issue with the marker lights, dome light and headlights as of late. I fixed the marker and dome today as it was a loose connection at the switch. The headlights have yet to work.

The weird thing about the headlights is if they fire they stay lit until I turn them off, the problem is they won't switch on now. Before I had to throw the switch 5-15 times to get them to light up, sometimes if I just left the switch on and drove for a while they would suddenly work.

I do have power out from the switch and the DRL circuit acknowledges the headlights are switched on but the ballasts never fire. It sounds like a relay is dead/dying or has a bad connection. Problem is I can't locate a headlight only relay as all the other lights work perfectly. Does anyone have an thoughts? Maybe know where the headlight relay is if there is one?
 

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NCOR
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8,449 Posts
Discussion Starter #3
Well thats what I figured but I bypassed the switch by connecting the brown power input to the yellow wire that sends power to the headlights(to a relay Ive got to believe as the wire is some pretty small stuff) and it turned off the DRL light on the dash just like when I turn the switch to the headlight position. So Id think the switch is good, but the relay must be bad. So where is the headlight relay?
 

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Registered
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264 Posts
I looked through my Haynes manual just now and I did not see anything for a headlight relay in either the index, electronics section, nor the wiring diagrams.

Even a brisk search on google showed nothing for headlight relays on our trucks.
 

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NCOR
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8,449 Posts
Discussion Starter #5
Exactly, hence why Im stuck. Neither my Haynes nor my Chiltons have a relay in it but somehow the little tiny wire from the switch gets power to the lights. It would seem like way to much current to try and pass through the little wire so a relay must be there somewhere right?
 

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The Treasure State
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288 Posts
Well there is only one way to find out if the wire coming out of the switch is what powers the bulbs. Disconnect the connector out of the switch and also out of the head lights and using a DMM (digital multimeter) measure for continuity between the two points. If there is continuity (ie ~0 ohms of resistance) then the switch directly powers the lights, otherwise there is something in between them. Gut feeling says that there SHOULD be a relay, but I honestly don't know, I'll check my Helms manual and post up my findings.

EDIT:
Looking at the circuit diagram for the headlights it appears that it goes from the headlamp switch to the DRL module where it feeds into and out on the same pin, I am going to assume that this is so the DRL knows when the headlamps are requested on, from there it goes to the headlamp dimmer switch and then on to the headlamps. However, I do have a few questions. Do the DRL actually work, not just the light on the dash, but the headlamps themselves? Do they work consistently? What about the high beams? Do they work consistently? The reason I am asking is that for the low beams the power goes from the dimmer switch into the DRL relay onto the bulbs, where as the high beams go from the dimmer switch directly to the high beams.

Conrad
 

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NCOR
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8,449 Posts
Discussion Starter #9
Conrad, the DRL's haven't worked since I bought the truck almost 4 years ago. The high beams work every time. Hrm, where is the DRL relay I wonder, off to go look.
 

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NCOR
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8,449 Posts
Discussion Starter #10
PartsAmerica part # RL36031
Ignition Accesory Relay: Headlight Relay: Can use alternate number {DR5016} Canada; With Daytime Running

I can't find that relay anywhere in my diagrams, I can't find it physically under the hood or under the dash. Where is it?
 

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The Treasure State
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288 Posts
The DRL relay is located in the "Convenience Center" this is the connection block located to the upper left of the brake pedal on the interior of the cab. The DRL relay should be in the bottom row second from the right. I believe that short of running quite a few more tests with a DMM that this would be the first thing to try. You should be able to short the tan and purple wires that connect to the relay together to test if the relay is the problem, this will make the headlights work but completely bypass the DRL function. You can try this first if you can figure out which wires they are looking at the "Convenience Center."

There is also a diode that may have burned out which could be the cause of the lack of DRL function, but this diode has no effect on the low beams working with the headlamp switch. Lastly there is a possibility that the DRL module is bad, however this seems unlikely and we can diagnose that later if the relay doesn't fix the problem.

Summary: Replace the DRL relay and report back the findings.

EDIT: Keep in mind that my Helms book is for a 1998, so while I would hope it is the same, some things might not apply to your 1997.
 

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NCOR
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8,449 Posts
Discussion Starter #12
Yea, once I located a relay for the system I ordered it last night. My email says its waiting for pickup at my local Kragen so Ill snag it on the way home from work here in a half hour and plug it in when I get home.

I checked over that panel but I think you are right, that middle relay was not labeled so hopefully a simple switchout will cure this ever so annnoying problem. Thanks for all the help so far man. I knew there was a reason we had EE's around:crazy:
 

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NCOR
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8,449 Posts
Discussion Starter #14
Well the relay fixed it, thanks for your help Conrad. You really made it go easier. Best of luck on your project, its good your not trying to trouble shoot it last minute.

There is no relay stock. Why do you think one has to be added to power extra lights off the headlight curcuit?
No relay, really? Hmm.
 

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NCOR
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8,449 Posts
Discussion Starter #17
It is more than just a little obnoxious. I have to drop the tranny and rebuild it to, woohoo, sigh.
 

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NCOR
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8,449 Posts
Discussion Starter #19
It still runs, just pukes fluid sometimes, whines at idle and smell of burning ATF even though the fluid looks bright red. Oh well, luck of the draw and I picked bad. Time to go shopping for goodies.
 
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