Electrical issue - Lights

[crazedyak]

From what I can tell it is isolated to the lights. Here's what I know from some quick trouble shooting...

All brake lights and turn signals function as they should. Even with the headlights on.

When I pull the headlight switch on... The lights come on, but I get no running lights, and the center and rear dome lights come on. No dash lights at all.

I recently put in a new radio, and as far as I can remember, only used the original wiring from the factory stereo.

I also had the dash off for a bit while I repaired some minor dash cracks, and repainted it. I did take apart the instrument lens to clean it and the gauges some.

Luckily I drive the Blazer 99% of the time during daylight hours. I just want to get it fixed, because driving with no running lights, and the entire interior lit up by the dome lights is a no-go for me.

 

[blazin' j]

Maybe its the headlight switch??? I have this exact same problem & don't know what it is either...

 

[shaun89]

im not sure how the inside of the headlight switch is wired,but im with him. my guess would be the switch is being grounded in areas its not suppose to be inside. does anything odd happen when u roll the headlight switch to "turn on" the dome light? (even though its on already) how about when the headlights r off. is the dome light still on? or do u have to roll the switch and turn it on?

 

[blazin' j]

I've changed mine once already cuz of it acting jus like uve stated...the headlights would even cut off while I was driving...I have noticed a leak n my windshield n the btm lefthand corner so it may b a moisture thing also...

 

[crazedyak]

Moisture is a definite possibility. Hurricane Irene visited me recently.

If the light switch is off then the dome lights are off. If I roll the headlight switch the dome lights do activate like the should.

If the lights are on and I roll the switch nothing at all happens.

I'll order a new headlight switch just to see I guess. LMC and Brothers both carry it. Tried local part house, and they don't have it in stock. Good times.

 

[blazin' j]

They are pretty cheap so I wouldbnt recommend ordering one if I have to pay for shipping...

 

[crazedyak]

Looking for any help available... I just got back from the middle east, and I've spent the last two days trying to troubleshoot this issue...

So here is what I know.

1) 20 Amp - tail/courtesy fuse blows as soon as Headlight switch pulled to ON position... in OFF position fuse does not blow.

2) Ran OHM continuity check with lead on constant power of fuse block and not getting any reading on multi meter with headlight switch in off position while getting solid 13 VDC across fuse.

3) Ran OHM continuity check on under dash courtesy light... nothing abnormal.

4) Just for shiz and giggles I did replace the Headlight Switch with no change.

5) I traced every wire I could get to and look at and did not find one single break or sign of a ground... but there must be one somewhere.

6) Tomorrow I plan to begin troubleshooting the rear running lights and parking lights... but I don't feel I'll find anything.

DOES ANYONE HAVE ANY ADVICE?

 

[bigred88]

When I put my new, modern head unit it, I lost my tail lights, as well as a whole slew of other things, because the fuse would blow as soon as I turned the headlights on, just like you're saying. I never discovered the true problem, but my fix was to wire the stereo to a new, separate fuse. I don't have a wiring diagram, and I don't know what kind of cross over there is there, but something about the new head unit drawing more power, or potentially a couple wires being worn and shorting out under the dash? It's been like 5 years, so I don't remember the specifics, but I can get under the dash this weekend and refresh my memory if you want any more info.

 

[Russell]

Check that your ground wire coming from the main harness between where the headlight switch wiring comes out and where it enters the top of the fuse block is secure.

General rule of thumb is that if you turn one thing on, and something else unexpected turns on instead, you have a grounding problem.

 

[crazedyak]

I didn't even come close to doing any troubleshooting today. I spent the entire day at the pool with the wife and kids. I definitely had more fun there than tracking wires in the heat.

I'll definitely trace out the headlight harness for a ground. I took the entire dash apart again last night to look around in there and could not find anything out of the ordinary.

I will also look at the new radio head unit which does seem the most likely culprit as these problem started soon after I installed it.

Thanks ALL.

 

[Russell]

I didn't even come close to doing any troubleshooting today. I spent the entire day at the pool with the wife and kids. I definitely had more fun there than tracking wires in the heat.

I'll definitely trace out the headlight harness for a ground. I took the entire dash apart again last night to look around in there and could not find anything out of the ordinary.

I will also look at the new radio head unit which does seem the most likely culprit as these problem started soon after I installed it.

Thanks ALL.

Just make sure that you check that one ground off the main trunk of the harness just above the e-brake cable. It usually is connected to a metal bracket on the e-brake cable assembly through a ring eye terminal. The rest of the grounds in the cab terminate on that metal bracket. I've seen that ring eye terminal break pretty regularly and it causes all kinds of fun with your electrical system.

Your headlights have a ground on the inside of the core support just above the head lights on both sides. There is a ground for the tail lights behind the reflector on the driver's side of the truck. There are multiple grounds located in the engine bay to tie the engine to the frame, the frame to the cab, engine to the frame and the engine to the cab.

 

[crazedyak]

Dang Russ... you seem to know where every single ground is, guess you've played this game before


well I just figured it out... new radio head unit it was the issue. I guess it was pulling too much power, so it looks like a new power source is in the works.

I put in a new fuse and disconnected the radio constant power wire and fuse popped when headlights switched ON. I then also disconnected the radio ground cable and the ignition switched power cable and no fuses pop and all lights work perfectly.

I need to troubleshoot this in the morning, but either the new radio is pulling too much power for that fuse, or the radio ground is bad. I'll find it in the morning after I make a trip to get a new multi meter. Mine broke about 30 minutes ago from a fatal collision with the driveway from my stupidity of placing it on the hood and not paying attention.