Need help figuring out electrical issues!

by Bruisr Wed Nov 14, 2012 1:01 am

Issue #1 When headlights are turned on low beam, top 2 headlights work while bottom 2 lights are dimly lit. When using hi beams all 4 lights work fine. The hi beam indicator in dash is dimly lit when on low beam and bright when on hi beam. This problem has burned out 2 light switches already! I've replaced the light switch 2 times and tested the hi beam switch with a known working one from my 73 sprint, I've checked wires and find no problems.

Issue #2 When using running lights only or when headlights are on, I have no front marker lights or bumper lights. When all lights are off left and right turn signals work fine, when lights are on left front turn signal is very slow to blink. Right side is unaffected. Also when lights are on and no signal is being used, left turn indicator in dash is constantly lit. I've checked all wires leading to front end and find no problems. I'm seriously stumped! Please any suggestions may help!

by bigredlaguna Wed Nov 14, 2012 2:18 am

Make sure all your ground connections are good. I can't tell you where they are at the moment, but find any wire attached to body metal and disconnect it and make sure it is not corroded or dirty.

There are ground straps that electrically connect the body to the engine, engine to frame, etc. Make sure they are connected. I once had a weird problem with dash/radio operation that was solved by re-connecting the ground strap from the firewall to the hood.

I also had weird light operation in the taillights that was due to bad grounds in the harness.

by texan01 Wed Nov 14, 2012 9:23 am

Yup, you've got a bad ground in the front light harness, they ground to the core support on each side, start by checking those, then work backwards, making sure that the body is grounded to the neg terminal or to the engine.

by thatfnthing Wed Nov 14, 2012 3:24 pm

Yep, bad grounds up front. Electricity is like water -- it will always take the path of least resistance, so if the ground that it was intended to go through is poor, it will go where it isn't supposed to because it found an easier path, which will get you stuff like burned out switches and indicator lights that are constantly on.

by pila Wed Nov 14, 2012 9:34 pm

A '74 with 4 headlights ?? The light harness that runs across the core support may have some problems. Inspect the whole harness up there for taped up joints etc.....

by texan01 Wed Nov 14, 2012 10:55 pm

Wait... did you do a quad light conversion? If so, I bet you've got your ground to the low beams mixed up.

by Bruisr Wed Nov 14, 2012 11:59 pm

I'm sorry I failed to mention this is on a 76 GMC Sprint. I own 3 G-3's. My very first car Since 16 yrs. old 1974 chevelle, 1973 GMC sprint with a '73 laguna nose, and the problematic 76 GMC I bought for my son. Thanks for the info. I'll check the front wire harness for grounds, I don't remember seing a ground strap from the hood to the firewall, which makes me wonder what other ones are missing. I'll post results in a few days, be on the road 'til saturday. Thanks again.

by Bruisr Thu Nov 15, 2012 12:01 am

Do you guys think the grounds could also cause issues with the left turn signal?

by bigredlaguna Thu Nov 15, 2012 12:49 am

Bad grounds can cause all the symptoms you described.

The ground strap to the hood is usually attached at the same point as the one that goes between the firewall and engine. I don't remember if it is one piece or if they are separate. Sometimes they go missing over time because there is usually no problem if that one strap is removed.

by Brainstain Thu Nov 15, 2012 5:59 am

Neither the 74 wagon or my 76 coupe have the hood ground and I don't think my 76 Laguna did either.. The only grounds I found was the neg cable to fender and firewall to block..

by Dubie Thu Nov 15, 2012 9:21 am

Check your fuses & make sure the connections at the firewall are in good shape.

by texan01 Thu Nov 15, 2012 9:37 pm

74chevelle wrote:I'm sorry I failed to mention this is on a 76 GMC Sprint. I own 3 G-3's. My very first car Since 16 yrs. old 1974 chevelle, 1973 GMC sprint with a '73 laguna nose, and the problematic 76 GMC I bought for my son. Thanks for the info. I'll check the front wire harness for grounds, I don't remember seing a ground strap from the hood to the firewall, which makes me wonder what other ones are missing. I'll post results in a few days, be on the road 'til saturday. Thanks again.

I've only seen one 73-77 with a ground to the hood, and its a California built car sitting in my garage. the two Arlington built cars I've owned didn't have a strap to the hood. This CA built car has all sorts of noise filtering on it that I've not seen on any other car, kind of interesting.

The grounds should be coming out of the plug for the dual headlight harness at the core support on both sides, and then it runs all the way back to the fuse box/firewall plug. that reminds me I've got to pull the harness off my junker 77 since it won't be needing it anymore and box it up for now.

by Tom77 Fri Nov 16, 2012 8:20 am

Also check the switch on the floor for the high beams. Lots of junk gets in there.

by pila Fri Nov 16, 2012 7:02 pm

My '77 Elco had a ground strap to the hood, and one to the top of the air cleaner. The idea was to keep noise down on the AM part of the radio. The ground bonding straps wouldn't cause the problems you have anyway.
You may want to check the sockets for the park/turn signal lamps in the front, as well as the front harness. The sockets get corroded some, over the years. And the two grounds mentioned here, one on each side of the core support, for the front lights, may need cleaning.

by Mcarlo77 Sun Nov 18, 2012 12:58 am

I'm chasing a similar problem on my '75 Laguna in that the front parking lights don't work when using the running lights or headlights. They do, however blink when turn signal is activated. Am going to install a different headlight switch tomorrow to see if that helps.

By the way, both the Laguna and my '77 Monte have the braided ground straps to the air cleaner and hood. I always assumed they were used to provide a stronger ground for the underhood courtesy light. Hey...I never said electrical was my strong point!

by Mcarlo77 Sun Nov 18, 2012 7:19 pm

Don't know if this will help with ideas 74chevelle, but I had a short time today to review my own front signal light problem. And, what I found is what drives me nuts with electrical.

Was going through the various light tests and confirmed again that my front signal lights weren't working whether using day lights or headlights. They would, however, blink when using the turn signal indicator. I also noticed the front side marker lights weren't illuminating this time around; even when using the turn signal. I pulled the sockets and noticed that the filaments on both sides were just barely glowing. For some reason, I went around back and this time I noticed the outer left rear bulb was also barely working when the turn signal was being activated. I knew that socket was good when I tested that harness before installing it, so I pulled it out and wiggled the bulb. Voila...it came back full strength. I went around to the front and discovered this allowed the two front side marker lights to glow full strength, too! Lesson here is that the problems you're having could be most anywhere within the circuitry. Unfortunately, it didn't do anything to light up the front parking lights.

by ant7377 Sun Nov 18, 2012 7:41 pm

I replaced the sockets for both my front parking lights recently .The old one were totally corroded inside and I would occasionally get one not working Id shake it and it would work. They sell them in the parts store still with pig tails to splice them in, after that all seems well.

by 77mali Sun Nov 18, 2012 7:45 pm

LOL

Had a problem this weekend with my D/D. None of the parking lights worked but headlights, signals, break lights all worked fine. Turns out the relay was shot.

by pila Mon Nov 19, 2012 12:24 am

Bad grounds are what causes lamps to barely light, because the dim lamps are getting a ground source from the other lamps. Follow the wiring on the rear lights, from the sockets, & find the black ground wire & follow it to the ground screw on the frame back there. I typically use a stainless steel screw on grounds after cleaning them. Up front, like mentioned, the grounds on the rear side of the radiator core support may be a problem, and are also black wires. If a car is rusted in the right places, the core support may not be grounded good to the frame & body etc. Adding a few good grounds between the body & frame, and core support to frame, and engine to frame, will save a lot of headaches down the road, and will also eliminate low voltage problems.

Need help figuring out electrical issues! P1010793

Need help figuring out electrical issues! P1010793

Here's a body to frame ground wire on my Elco project, for example..

by 1973 454 MONTE Mon Nov 19, 2012 8:43 am

try using a 4 light harness from a 76/77. it just unplugs from the back of the fuse block.

i had the same problem on my caprice. i tried to just wire in the euro-lights.never got them to work right. so i pulled a harness out of a 87 and they work like they are supposed to,and i have no cut wires.

by Bruisr Tue Nov 20, 2012 11:11 pm

I've tried several light switches with the same results. UPDATE: I added the ground strap from the engine to the frame and firewall, cleaned the grounds located next to the headlights themselves, no change! Upon searching the front harness I noticed the headlight plugs looked odd. I learened that the tan wire and the black wire going to the headlight plug were not in the proper location. I corrected it, it helped. Not 100%, but alot better. The hi beam lights still have a faint glow on low beam operation, but much improved.. Still not solved. I have a feeling someone redid the front harness. The wire colors seem to be in wrong places. I'm going to strip the harness out and redo according to diagram I have. Still dont know what is causing the left turn indicator to stay lit and why I have no front running lights!

by Bruisr Tue Nov 20, 2012 11:13 pm

Thats where I attached my new ground strap to, and over to the engine where the spark plug shields used to bolt to the side of the block.

by pila Tue Nov 20, 2012 11:37 pm

Did you add a ground to the core support, from the frame ? It may help....

Do you have a schematic diagram of the front lights ? If not, I may be able to send you that section of the diagram.

by Bruisr Tue Nov 20, 2012 11:39 pm

Good Idea, I will do that! After what I saw with the front headlight plugs, I'm gonna take a hard look at the front harness, to see what I might have to rewire!

by Bruisr Tue Nov 20, 2012 11:43 pm

I noticed last night while driving to work My 73 elco is sharing the same problem as my sons 76 elco, the front left turn indicator in the dash is constantly lit. However I also learned I have a burned out right front signal light and marker light. I wonder if they are both the same problems, I'll have to wait til the weekend to find out.

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