Electrical Help Needed

Been trying to pinpoint a problem I've had with '75 Laguna project from the day I brought it home and can't seem to make any progress. Problem is the front parking lights and front side markers don't light unless blinker is used. Well...to qualify this some more, I do get a faint glow from the side marker lamps, but you have to pull the socket from the fender and look at the bulb to see it. All other exterior lights seem to work just fine. One other clue...both dash indicator bulbs are lit when Headlight Switch is pulled. Everything points to a ground issue. But, I've cleaned the two radiator core support ground connections. I've replaced the tail light harness and cleaned the ground connection in the trunk. There's a ground cable coming off the neg. battery cable attached to the fender...not 10" from the right side rad. core support ground that supports the RH headlight/parking light. Ground wire from engine to firewall and firewall to hood. Just don't think it's a problem with enough ground wires to the body/frame...but, what do I know?

So, having studied the schematics, it appears to me that the Brown wire, that runs from the Headlight Switch, feeds the four lamps in question (along with the tail lights). Am I correct to assume this is where they get their power when the Headlight Switch is pulled half-way out? Checked each socket at the Brown wire connection and they are getting full voltage. Of course, there are no ground wires to the side markers...so, I traced the Brown wire to the tail light harness and it appears to me they get their ground from the trunk ground? Also, seems to me the Dash Lamp Indicators are fed by the Lt. Blue and Drk Blue wires that also feed the front four lights in question. Again, I assume these are only live when the blinkers are used? I'm stumped...I don't know where to go from here to trouble-shoot this. Any suggestions...or, corrections to my logic?

Have you tried a new switch, could be an internal problem with yours.

Are you sure you've got all the grounds checked?  There's quite a few, LOL.
Check you connections @ the fuse box?  I also seem to remember a couple of grounds that are kind of obscure.  1 is just above the drivers kick panel- might have to remove the panel to see it and there is another under the dash as well that is connected to the harness that might have to do w/ that brown wire.  Can't recall for sure where it's screwed into but check there as well ... maybe above the pedals somewhere up in the underside of the dash.  Good luck- I HATE ELECT. GREMLINS.

You should be able to run a jumper wire on the ground side of the socket....if the bulb gets bright then you have a ground issue. I'm thinking something is cross feeding in the switch, those rotary dials go bad...corrosion on the contacts.

I had a 79 Z28 with a similar problem. The brake lights wouldnt work and the signals would not blink neither would the hazards but they lit. THere is a ground in the fuse box on that car that was corroded. I had to take the box apart by taking out the bolt in the engine compartment and then cleaning the ground inside the box with some sandpaper and then a little grease to keep it clean. Worked fine after that. Look at the schematic in the service manual.

I've installed a different Headlight switch and High Beam Switch.  No change. I've checked continuity of the ground wire from the engine side of the fuse box to each of the rad. core support grounds and there is no resistance. Of course, the two front side markers don't have a ground wire...just brown wire and light blue (LH side) and dark blue (RH side). Besides, if they all work when blinkers are used, doesn't that prove the grounds are solid?

I can't be sure if I've found all the ground wires.  I know of the one on the bottom of the dash...forward LH side.  Trying to remember what other ones there are. You'd think I'd know as I have removed several dashes...one as recently as three weeks ago.  Always rushed for time, so don't pay much attention as I'm disconnecting everything.

Check the ground for the blinker and flasher relays. I believe that is what was wrong with mine and that was the ground i mentioned if i remember right.

How are the metal connectors where the bulbs go? It's kind of odd that all of them are doing this but give them a clean & use some dialectic grease on the end of the bulbs.

Perhaps also there is some fraying or a loose splice in one of those lines somewhere. I'm sure you checked this but is there a dedicated fuse for them? Strange that they work when the blinker is on is there any common connection where the harness clips in to the steering column?

Another thing is just try another pig tail maybe one side is bad. I think I replaced all of them on my car.

I'll do some more research on the grounding issue. I, too, am wondering if there isn't something going on with the turn signal switch/wiring. Wish somebody could explain exactly how that works with the front lights when the side markers don't have the usual black ground wire...and yet, the front parking light sockets do have a ground (to support a larger bulb?) I just don't know enough about electrical outside of the std. hot wire/ground wire to each socket. For instance, does the Lt. Blue wire (LH socket) and Drk. Blue (RH socket) act as the ground through the turn signal switch? The rear side markers are a two-wire set-up and they have a black (presumably ground) wire...and, they are on the same circuit as far as I can tell. Very confused...

Mcarlo77 wrote:I'll do some more research on the grounding issue.  I, too, am wondering if there isn't something going on with the turn signal switch/wiring.  Wish somebody could explain exactly how that works with the front lights when the side markers don't have the usual black ground wire...and yet, the front parking light sockets do have a ground (to support a larger bulb?)

Basically the side marker lamp/turn signal are on the same circuit, and therefore both ground through the turn signal ground, and when the directional is on, the two lamps alternate.  I had this all figured out when I rewired the car, but it's a little hazy a couple years later, so I will try to look at my diagrams tonight and maybe cook up a graphic that explains it better.

Anything would be helpful...thanks.

I also confirmed I have continuity from the engine side of the fuse box thru both the Lt. Blue and Drk. Blue wires to each designated bulb. So, I can only conclude the problem lies somewhere within the turn signal switch?

One more question that I have...if the side marker and parking lights are interconnected, and the marker lights are grounded thru the turn signal switch, wouldn't that also be the case with the parking lights? If so, why do the parking lights have their own ground wire? Still confused...

The core support may need a good ground wire running to the body.(?) On mine, I ran ground wires from engine to body, & core support to body. Seems like we can't have too many grounds....
When cars get this old, even the front fenders may not be a really good ground.

I tried temporarily attaching a ground strap direct from the Neg. battery terminal to the core support and nothing. Can't help but think something is amiss under the dash (wiring) or the turn signal switch. Just confusing as everything else works; including tail lights, headlights, flashers, blinkers, back-up lights, rear side markers, hood light, trunk light, dash lights. The way I figure, if there is enough grounding for all that, the problem must be elsewhere.

If the park lamps are inoperative check the headlight switch...if test lamp lights at switch terminal No.4 (brown/white wire) but not at terminal No.5 (brown wire) replace defective light switch. Right out of the manual.
Bulb filament provides the ground path for the marker lamp bulb through the light blue or dark blue/ white stripe wires

I swapped out the headlight switch with another used one with no change. I've got voltage to the parking lamps thru the Brown wire...as well as to the marker lamps. Got continuity from engine side of fuse box to each relevant lamp through the Lt. Blue & Drk Blue wires, too. What confuses me with the parking lamps is they have their own ground wires; yet are interconnected to the marker lamps with a Brown wire and either Lt. Blue or Drk Blue. Why do they need two paths to ground? Why doesn't the separate ground wire allow the parking lamps to illuminate?

It sure can get confusing....
I got caught up because of a tail/stop light socket that was corroded internally, on the ground to the shell for the bulb.
So one way to check the sockets is have a grounded wire to touch on the socket shell for the bulb when there is power to the socket.

Mcarlo77 wrote:I swapped out the headlight switch with another used one with no change.  I've got voltage to the parking lamps thru the Brown wire...as well as to the marker lamps.  Got continuity from engine side of fuse box to each relevant lamp through the Lt. Blue & Drk Blue wires, too.  What confuses me with the parking lamps is they have their own ground wires; yet are interconnected to the marker lamps with a Brown wire and either Lt. Blue or Drk Blue.  Why do they need two paths to ground?  Why doesn't the separate ground wire allow the parking lamps to illuminate?

I dug out my diagrams and luckily they were still wiring it the exact same way in the 93 Caprice, whose diagrams are a hell of a lot easier to read.

The way the circuits work:

When you turn on the parking lights on the headlight switch, circuit #9 (BRN) has 12v to both the parking and side marker lamps.  As expected, the parking lamp grounds through the black wire to the core support and lights up.  The marker lamp does nothing, as there is no path to ground on the other side of the lamp.  When you turn on the left directional, circuit #14  (LT BLU) gets 12v intermittently; on the parking lamp it lights the second filament (causing it to get brighter) and grounds as normal.  The marker lamp, though, now has the juice flowing from the LT BLU to the BRN and then grounds through the first filament of the parking lamp.  This arrangement also allows the parking lamp to blink at full brightness even when the headlight switch is off, because juice is flowing through both BRN and LT BLU to BLK.  Ditto for #15 (DK BLU) on the right side.

The tail lamps are different, because those side markers have their own grounds and are always on -- they don't blink with the tail lamps.

So based on what you're describing, there's a problem with #9 BRN.  The ground is fine, otherwise the parking lamps would not blink properly when the directionals LT BLU/DK BLU are flipped.  Since you have 12v coming down the BRN wire and a faint glow on the side marker lamp (that was a good clue), the juice is flowing from BRN, then through the side marker and back up LT BLU to the dash indicator lamps, because those have a path to ground on the instrument circuit.  Since BRN is shared on both sides, the same thing happens with DK BLU.

So I would focus the hairy eyeball on the parking lamps themselves, and/or their sockets.  Since BRN has 12v, and the ground is good to the core support, there must be something wrong with either filament #1 in the bulb, or the socket itself -- the flow of current is being blocked and forced to go elsewhere.  Possibly a surge of some sort blew both those filaments, but I would also look for corrosion inside the bulb sockets.  

Hope that helps!

Dude...you are the Man! This is exactly the kind of information I was looking for. Now it makes sense as to how it all works. The bulbs are new, but I can try cleaning the inside of the sockets. Or, splice new ones in place. Thanks, much...I'll report back.

Mcarlo77 wrote:Dude...you are the Man!  This is exactly the kind of information I was looking for.  Now it makes sense as to how it all works.  The bulbs are new, but I can try cleaning the inside of the sockets.  Or, splice new ones in place.  Thanks, much...I'll report back.

Happy to help!

Dumb Q -- if the bulbs are new, did you perhaps accidentally buy the single filament ones (i.e. 1156 instead of 1157)?  This might also do it.  There should be two contacts on the bottom of the bulb and two visible filaments inside.

Thanks to the above information, I've made a little progress. Had just a brief amount of time to play with this today and discovered that when I removed the bulb/socket from the parking light housing and touched one of the metal ground prongs on the upper rim of the socket to a chassis ground, the bulb lit. That, in turn, lit the side marker light. Tried the other side and same results. Actually wiggled the LH bulb and wires to the socket and got it to stay on...until I tried pushing the headlight switch in and out. Then, nothing. Had to do the grounding of the prong again.

So, this would prove the sockets are getting voltage from Brown wire...right? Seems, then, that it's the ground that is the problem (what a surprise, huh?!). Also, since the headlights function properly and share the ground wire connections to the core support, the problem would seem to be either in the sockets...or, between the core support grounds and the sockets. Suppose next step (and, easiest) may be to try splicing a separate ground wire direct from the core support to base of socket to eliminate possibility of wire breakage between those two points. If that doesn't solve the problem, next would be to install new sockets. Sound like I'm on the right track?

And yes, I made sure I have the two-filament bulbs installed. Also tried cleaning up the two inner metal ground tabs inside the sockets, but didn't change anything.

Yep, that sounds like a good plan. Any time you have to wiggle something electrical to make it work, you have a broken wire or contact somewhere in there. Most likely point for a break is where the wire enters the lamp housing, as this is a high-stress point. Less likely, but also possible: corroded wire -- copper rusts just like iron, but slower.

Feeling a sense of accomplishment today after determining that BOTH parking light sockets were defective. Replaced them and all is well! Still confused with the continuity findings I was getting with my Ohm meter from core support ground to metal prongs on rim of socket. I'd get good readings...but obviously, the ground was broken inside the sockets somewhere. Anyway, couldn't have done it without your help, my friend. That description you provided of how the circuitry works should be a "Stickey".

Last electrical issue is determining why the horn doesn't work when you hit the strg. wheel pad. Tested horn and it works. Guessing either a bad contact inside the strg wheel...or, bad horn relay? Any way to test those?

Glad you got it working!

The horn is a pretty simple circuit.  Bear with me, I'm working entirely from foggy memory here, as my original wheel and wiring are long gone.  IIRC, there's one positive wire coming from the horn relay up the steering column to a conductive ring around the steering column, which then has a feed that rides on it as the wheel turns and connects via one wire to the contact switch inside the steering wheel pad.  When you press the pad, it simply grounds that circuit to the steering column itself.  This trips the relay, which then sends high current to the horn itself down circuit #29 DK GRN (nylon jacket).

Remove the pad from the steering wheel, and use a jumper wire to touch the conductive ring to the steering column shaft.  If the horn blows, the relay is good and the switch inside the steering wheel pad is probably the culprit.  If nothing happens, the relay is bad.