[1974gto]

Hope you guys can help. Here is my problem. Rewired the whole car with a new harness. My blinkers work fine until i turn on the headlights. I changed the headlight switch and checked all grounds. Still the same problem. Any takers?

[Bill Hanlon]

What do the blinkers do when the headlight switch is on? Stay on all the time? Off all the time? Same front and rear? Same left and right? Same high and low beam? What happens if the headlight switch is just pulled to the first click?

[1974gto]

Bill they do not do anything they are off. I will check when i pull the switch out to the first indent. I have also replaced turn signal switch as well. Grounding issue? I have checked and rechecked the grounds. Does the core support need a ground to the frame?

[Bill Hanlon]

If parking lamps and brake lamps work this shouldn't be a grounding problem as they share grounds with the turn signal lamps.

I'm looking for a wiring diagram on line somewhere to look for more ideas.

[1974gto]

Thanks bill, I will check it tomorrow and see if i can figure something out.

[paint guy]

When you installed a new harness, was the plug for the headlight switch attached or did you wire the plug in? I suspect that one of your wires to your headlight plug could be in the wrong position or attached to the wrong switch terminal. And you should have a ground from your core support to your frame.

[1974gto]

The headlight plugs were already attached, I did not ground the core support as there was not one there when i disassembled the car. I will try that this weekend., I will also check if the headlight wires are correct in the socket. Did not think about that!

[paint guy]

My previous post was not well written as it sounds like I meant the plugs at the headlights themselves, when in actuality I meant the plug at the headlight switch. But now that you mention it, it wouldn't hurt to verify both. I believe there is a terminal on your headlight switch that will provide power when the switch is pulled halfway out (parking lights) but does not provide power when pulled out all the way (headlight position), IIRC.

[1974gto]

I will check both, Have not had a chance to check this weekend. But both connections were already attached to the harness. Headlight and dash harness that is. Thank you for your help, hopefully i can get to it this week. I will keep you posted.

[1974gto]

OK, Here is what it is doing
Headlight switch off
Left turn signal-front grill works marker light does not ( does not blink )
Rear tail light and marker light work

Right turn signal-Front grill and marker work
Tail light only marker does not (blink)
4 way on- All rear lights work/ Front grills only (Markers do not blink)

Headlight pulled out 1 click
Left turn signal- Lights come on no blinking front or rear
Right turn signal- Front grill and marker work
Rear tail light works/ no marker

Headlight switch all the way out is the same as pulled out 1 click

Wiring, headlight switch, turn signal switch and fuses are all brand new. Install ground strap to the core support to the frame as well. Cleaned all grounds and mounting locations.

[Bill Hanlon]

I found what is supposed to be a wiring diagram for a 74 GTO on AutoZone's web site, but the wiring for the front marker cannot work the way it is drawn. Anyone have a better drawing?

[Engine-Ear]

Vexing problem!!

Just a thought: Did the re-wire include the steering column wiring? Makes me wonder if something was upset in that area when the wiring was replaced.

[rexs73gto]

Where did you get the harness's for the car. Next, when you ordered the front lamp harness did you order one for a car with front cornering lamps or without corning lamps. You may want to look at what harness you did order as there is a couple of different front lamp harness's for your car that if you got the one with cornering lamps will have a different wiring path for the lamps & grounds which will cause the problems your having. Also this may sound dumb, but did you make sure the bulbs were all in the sockets correctly. You said you replaced the turn signal switch ,,, did you have the new style that uses a jumper wire so it will plug in to the switch on the column?? I know it is going to be some extra work , but you may want to reinstall the old turn signal switch to see if that takes care of the problem to. Also did/do you have a tilt wheel in the car?? If so did/do you have the correct turn signal switch for what ever column you have in the car.??

[1974gto]

Originally Posted by rexs73gto

Where did you get the harness's for the car. Next, when you ordered the front lamp harness did you order one for a car with front cornering lamps or without corning lamps. You may want to look at what harness you did order as there is a couple of different front lamp harness's for your car that if you got the one with cornering lamps will have a different wiring path for the lamps & grounds which will cause the problems your having. Also this may sound dumb, but did you make sure the bulbs were all in the sockets correctly. You said you replaced the turn signal switch ,,, did you have the new style that uses a jumper wire so it will plug in to the switch on the column?? I know it is going to be some extra work , but you may want to reinstall the old turn signal switch to see if that takes care of the problem to. Also did/do you have a tilt wheel in the car?? If so did/do you have the correct turn signal switch for what ever column you have in the car.??

I got the forward lamp harness and dash harness from Lectric limited. I will have to call tech support to see what type of harness it is. The problems i am having are the same with the old headlight switch and turn signal cam. I replaced them thinking that was the issue. I am also using the Pontiac service manual electrical diagrams as well. I am going to retrace the forward lamp harness and dash today to ensure I have connected everything correctly. The turn signal switch did have the jumper wire so it matches the connection on the column. it is not a tilt.

[1974gto]

Bill, I have the 1974 Pontiac service manual with the wiring diagrams. I am going to try and retrace the harness again, make sure everything is correct.