# 66 Wiring issues



## jbrenner (Apr 15, 2013)

Hey everybody. I'm at my wits end with the wiring on my 66 that I'm in the process of restoring. I've completely installed the new wiring harness, EZ Wiring, and everything went smoothly. However, the issue I'm having is with the headlight switch and blowing fuses. I'm using a Ron Francis switch and every time I go to connect the brown wire that feeds the rear brake/turn signal lights, it immediately blows the fuse inside the fused wire I have running to the terminal on the switch that powers the rear lights. This terminal and the terminal for the brown wire are right next to each other. I've gone through the entire setup over and over looking for a short to ground somewhere and can find no evidence of any damaged wires or bare spots making contact with metal. Have also made sure everything is grounded including the park lamp and tail light buckets as I know they can be issues due to corrosion. Headlights work, turn signal and brake lights work, dash lights and gauge lights work. But without the brown wire connected I am left without rear running lights for night time driving. Something else interesting of note is that when I try to attach the brown wire on the terminal, it will literally "spark" when it makes contact. I can not for the life of me figure out what the deal is. Any thoughts or input would be greatly appreciated.


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## 05GTO (Oct 6, 2004)

Unplug the ribbon cable that runs under the drivers side carpet and see if the fuse still blows. If it doesn't you may have a problem with the ribbon cable or the trunk wiring.


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## jbrenner (Apr 15, 2013)

Yeah, I don't have the ribbon cable anymore as I installed an aftermarket wiring harness. I did try and run separate clean wires to the back, bypassing the ones I had already installed inside the car, to be sure it wasn't that. With the fresh wires ran for each circuit it still blows the fuse. Just went over everything again looking at all wires for any kind of breakage causing a short to ground and I just find nothing. Stumped!


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## 05GTO (Oct 6, 2004)

Do you have a wiring diagram for the new switch?


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## jbrenner (Apr 15, 2013)

Yes, switch comes with one and it's definitely wired correctly. It's the standard GM connections. The fuse blows as soon as you pull the knob out to turn headlights on. Got a new switch also, thinking it may be a bad switch. No luck. Basically I can't have both the fused 12v wire that powers the taillights AND the brown wire that runs from headlight switch to tail lights connected at the same time. If brown only connected, no problem. If fused power wire only connected, no problem. Brown wire obviously runs all the way back to rear lights. Based on how it's acting, blowing when I try to connect both tail light wire and fused power wire, my thoughts were that there had to be a short in those sections somewhere. But to no avail. Wires are undamaged and fuse still blowing when new different wires used to "bypass". The rear tail lights ground via the housing he sockets plug into, but I've got additional ground wires connected from ground on socket to post on housing as well. Ground shouldn't be issue anyway since it'll usually cause lights to be dim or not work. Not blow fuses.


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## tonyli (Aug 14, 2013)

Bad grounds will cause issue with lights dimming. However dead short(pinch wire) will cause the fuses to blow. Can you take some pics of the light sockets and how you set up the grounds. Also do you have meter with a ohm setting on it. You can check for grounds this way.


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## jbrenner (Apr 15, 2013)

I can take some pics this weekend. Mine is a 66 Tempest, so it has the curved shaped tail lights in the corners of the rear end. Anyway, the tail light housing is 2 pieces, interior and exterior. The interior bracket slides over two threaded posts from the exterior piece, and the tail socket plugs into the hole in the exterior piece. The metal edges of the socket contact the metal housing for ground when you plug it in. Additionally I've run another ground wire that on one end connects with the black ground wire coming from back of socket, with other end attached to nut that tightens down on the threaded posts on the tail light housing.

As far as grounds go, I've got engine block to firewall, engine block to frame and passenger side inner fender well to frame all connected...and connected to bare metal as should be. Have battery cable to engine block as well as should be.


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## ALKYGTO (Mar 29, 2010)

Does the brown wire have voltage to it before you plug it in? May be feeding back from the rear if you have two power sources running back there. I know electrical problems can drive you nuts. :crazy:


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## jbrenner (Apr 15, 2013)

Yeah, thought about that too. Tested brown wire to check for feedback/current and the multimeter reads nothing. I've also tried disconnecting different things one at a time...a dash light, gauges, etc...to see if that would effect anything and it hasn't changed. But it does almost act like there's current running through it since it literally sparks as soon as it contacts the tab it connects to on the headlight switch. As I mentioned before, if only fused 12v wire connected, no problem. If brown wire from rear of car only connected, no problem. As soon as I try and connect both, spark and then subsequent fuse blowing if I hold the wire to the tab on the headlight switch long enough. Does this whether the 12v wire is connected first and I then try to connect brown wire, or vice versa...brown wire connected to headlight switch first, then 12v fused wire.


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## tonyli (Aug 14, 2013)

The two wires coming from the light socket are two hot leads. One has power coming from the running lights and the has power coming from the brake and signal switch. If am reading your post correctly you have an additional ground tied into the black wire. You have to remove that additional ground because that is your short. The only ground that is needed when the socket is screwed into tail light housing. Let me know how you make out with the ground removed from the black wire.


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## jbrenner (Apr 15, 2013)

Thanks tonyli, that's exactly whag it was. In my haste I attached the ground to the black lead, instead of the bezel where the ground actually feeds. One of my rear lights was dim at the time, so added additional grounding wire to correct...but not thinking and used the black lead off the socket instead of the grounding from the housing. Stupid, really. These things happen though in a total restoration, so many things to restore and consider. Anyway, thanks again for the assistance. Now onto installing the vintage air.


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## tonyli (Aug 14, 2013)

No problem. Glad it work out.


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