Jump to content
Sign in to follow this  
2poniesngarage

Headlights powered on only when car is started?

Recommended Posts

So I have 2 69's and was adjusting the hedlights on them both. Both have original wiring system.

One the headlights come on when I pull the switch out.

The other one they dont come on until the car is started.

What gives here. Anybody know what the difference is with them.

Share this post


Link to post
Share on other sites

Power to the headlight switch is from the battery, bypassing the fuse box.  The one car that doesn't have them come on until the car is started suggests that either there's a huge power relay for the underdash harness, or the main power to the headlight switch has been changed from BAT to ACC somewhere in the underdash wiring loom. 

I'd put my money on the second possibility.  You won't believe the crap the PO's (previous owners) decide to do...

Share this post


Link to post
Share on other sites

Ok, It doesnt bother me that it does that, cause I have to remind myself if I drive early morning to turn them off after the sun comes up enough that I dont remember they are on. This way they go off when I turn the key off. But didnt seem to be the way it should be to my memory of that year cars. Wonder if it would be a wire size problem that could bite me if they are on for a while. I dont drive hardly any at night but dont want it to be a hazard either. ( fire is what i pondering)

Share this post


Link to post
Share on other sites

I'll look into it this weekend if time allows. But the correct way is when you pull the switch out, the headlights should come on. Regardless of the key being on and certainly not dependant on the engine running. Tks to the gurus here on your time to reply to the issues.

Share this post


Link to post
Share on other sites
23 hours ago, 2poniesngarage said:

But the correct way is when you pull the switch out, the headlights should come on. Regardless of the key being on and certainly not dependant on the engine running.

Correct, if the system hasn't been modified, then there is no connection to the ignition switch (as you'll see on the schematic). Since you said "Both have original wiring system" I have to assume its a high resistance connection somewhere in the headlight circuit that is overcome when the alternator starts charging at a higher voltage than the battery. The battery is around 12v and the alternator should kick out around 14v. The higher voltage will push more electrons through the high resistance connection and your wayward headlight shines.

Remember, the schematic is intended to show you how it works,  and a wire diagram will show you how its wired with all the plugs and connections, etc.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  



×