Bypass dome light switch? 1969 GTX

[threewood]

Finally hooked a battery up to test the lights in my 1969 GTX non rally dash. Turn signals work, hazards work, headlights work, dash lights do not work. All courtesy lights work (dome, console, glove box and trunk light)

When I first turned the lights on they did work because my tach light was on (hooked into printed circuit board lights). Then it didn't, popped a fuse. Replaced fuse now when I operate the light switch to 2nd and 3rd position the headlights come on but my ammeter shows a big draw and if they stay on for a few seconds the fuse blows. I think I have a short to ground somewhere. I swapped out the headlight switch and same issue.

I want to bypass the dome light switch on the dash to rule that out? Does anyone know which wires to jump?

 

[BeepBeepRR]

If I am looking at the schematic correct You can jump the black and yellow that are both in the same spade in the connector to the tan wire. The separate yellow feeds your dome light and map light if equipped. Tan comes from the fuse panel and goes through the switch to the black which also feeds the light switch. Err black with yellow together its not just a black wire on that terminal.

 

[threewood]

Ok, thanks. That makes sense.

I'm going to try and trace some wires. The fuse that keeps blowing is the 20A tail lamp/ stop lamp fuse. When my front marker lights are hooked up, no lights on, turn signals work both sides. But when I move headlight switch to middle, no driving lights and the ammeter pegs to the left, move switch to lights on position and front and rear lights come on. Rear lights are bright and flash with turnsignal fine. If I leave the lights on the 20A fuse blows.

Front turn signals unhooked, tach light comes on, pull headlight switch out and ammeter drops a touch like it should. Still no dash lights.

 

[threewood]

Messed around with it today. I tried another headlight switch that I took apart and cleaned. Same issue...once the switch goes on it shorts. Pulled the plug for the rear wiring behind the kickpanel = still shorts. Pulled the turn signal harness plug = still shorts. Pulled the front light harness and no short. When I unhook the front turn signals, it does not short but still no dash lights. If I touch the bulb housing to ground the ammeter pegs right and melts the fuse.

Tried all this with a ground strap to cluster. I also swapped in a new floor dimmer switch = no change.

With the light switch off, turn signals work fine (front and rear) and hazard works fine = no draw on ammeter. Ammeter only goes ape $hit when the headlight switch is in park or headlights on.

 

[440+6]

Try unplugging the dimmer switch, does it still blow a fuse?

 

[BeepBeepRR]

See if you have a multi terminal on the fuse box with pink wires going to it. If so take one spade off of that terminal and see if that gets you anywhere. By the schematic its the 3rd fuse from the left. You can see 3 pink wires coming off of it. Which feeds the windshield wiper switch, stop light switch and the headlight switch. Taking the plug loose at the wiper switch would also be a way to narrow it down to either lighting or the wiper being the issue. Since you have all three fed from the same fuse it has to be one of the 3 causing the issue.
In the picture below are the terminals Im talking about. There should be pink wires 3 of them piggy backing off one terminal like the others in the left side of the picture. Take one pink wire off at a time and see if it changes your outcome. This picture has orange ones piggy backing but the pink ones should do the same.




Actually this one is better. Look at the pink wires in the 3rd terminal from the right in this case . They show them here piggy backing. That is the place to remove one and test again.

 

[threewood]

Try unplugging the dimmer switch, does it still blow a fuse?

The floor dimmer or dash dimmer?

 

[threewood]

See if you have a multi terminal on the fuse box with pink wires going to it. If so take one spade off of that terminal and see if that gets you anywhere. By the schematic its the 3rd fuse from the left. You can see 3 pink wires coming off of it. Which feeds the windshield wiper switch, stop light switch and the headlight switch. Taking the plug loose at the wiper switch would also be a way to narrow it down to either lighting or the wiper being the issue. Since you have all three fed from the same fuse it has to be one of the 3 causing the issue.
In the picture below are the terminals Im talking about. There should be pink wires 3 of them piggy backing off one terminal like the others in the left side of the picture. Take one pink wire off at a time and see if it changes your outcome. This picture has orange ones piggy backing but the pink ones should do the same.
View attachment 430151



Actually this one is better. Look at the pink wires in the 3rd terminal from the right in this case . They show them here piggy backing. That is the place to remove one and test again.

View attachment 430152

Here is the back of mine. It has a few pink as it has the light package...

I was going to pull the fuses to 2 and 3 and trace back to look for any open to ground.

I was really thinking it was my front park lights but they have to be hooked up correct. 1157 lights, 2 prong connection and the base is grounded. With the light housings not grounded it doesn't blow, ground the housing, park lights work but fuse blows.

I did try it with the wiper motor unhooked, no change.

 

[440+6]

The floor dimmer or dash dimmer?

dash

 

[miller]

With the light housings not grounded it doesn't blow, ground the housing, park lights work but fuse blows.

Sounds like a dead short.
You might try isolating the park light wires, by pulling the bulbs, and the fuse for that circuit. Then, check each wire for contact with ground. If one is grounded, there's your short. Even narrow things down, by pulling the firewall plug for the lights harness, and re-check it. Most likely it's under the dash, and checking the wires at the firewall block, to ground will tell you.
Good luck on it!

 

[Billccm]

You probably are aware of this technique, but I'll mention anyway. I take a test lamp and place across the blown fuse terminals. The lamp will glow brightly with the short circuit. While watching the lamp glow, start unplugging harnesses. When you find the harness that leads to the short, you can either use an ohm meter, or test lamp in series with the shorted 'branch' of the tree. Then proceed.

 

[threewood]

Ok, I am pretty sure the problem lies in the harness. I double checked engine compartment wiring to lights / signals / wiper motor and they were all correct, plus they are all new harnesses.

So I pulled the three connectors from the bulkhead and started probing for short to ground using resistance. On middle connector (J, connection for fusible link) it was grounded somewhere in the cabin. So I went to the fuse block and started probing and the 1st three fuse connections on the right are grounded. I pulled the dash dimmer switch and connected my lead to the tan harness connection and touched the other to ground and no doubt, it is grounded.

I pulled an old harness I have out and started messing with it and it seems wires like to melt together so I am guessing that may be what happened. If I am off base or need to do more checking, tell me. As of right now I am going to pull the harness and take it apart. New ones are $475 so i am going to raise this one from the dead lol.

Below are the fuses that are positive to ground...

 

[miller]

As of right now I am going to pull the harness and take it apart. New ones are $475 so i am going to raise this one from the dead lol.

That's what I did on my 64. Had two used and abused harnesses. Set up a harness pattern on a piece of plywood, marked all the connections, took apart both harnesses, and rebuilt one good one, using the best wires. If a wire was too old in either, just made a new one.
Main thing is your getting somewhere on it. Fun stuff.
btw...Looking at web connector companies, I was able to find what I needed.

 

[threewood]

That's what I did on my 64. Had two used and abused harnesses. Set up a harness pattern on a piece of plywood, marked all the connections, took apart both harnesses, and rebuilt one good one, using the best wires. If a wire was too old in either, just made a new one.
Main thing is your getting somewhere on it. Fun stuff.
btw...Looking at web connector companies, I was able to find what I needed.

Thanks. The connectors are in nice shape and the factory wrap looks good to which is why I didn't crack it open when the dash was out. I am working on getting it out right now.

I like the idea of a board. I am going to try that and use zip ties to keep the legs together for inspection.

 

[threewood]

Got it out and unwrapped and did not find a single scorched wire or any chaffing. The wire is still supple and I checked from one end to the other. I should have removed all the fuses before checking. The only wire I found with chafing was the solid brown going to the wiper switch and it was scrapped off and not melted, which I fixed. Cleaned the harness up and put it back together.

Bonus= I have to remove the instrument cluster to fix the orange pin which came off during disassembly.

Once I get the harness back in I will leave off the accessories and plug them in one at a time. At least i know my harness is in good shape.

 

[miller]

Don't know if it will help. But, I checked each wire, from end to end, with an ohmmeter, for any resistance. That will tell you if the wire itself is in good shape...if it's burnt/corroded somewhere, resistance goes up.
I'm tracking down an issue on mine, and wound up a couple bad connectors in the fusebox. Fuse good, but ohmmeter across the two fuse connectors...no! Terrific!!

Doesn't take much, to make a bad day. Might also, using your wiring diagram, check off 'each' wire. Found off the main harness, can be separate single wires, that make things work, to complete that circuit. And, of course, any and all grounds.

 

[miller]

Might be off base, but have you checked to see if the headlight switch plug is wired right? Think I remember a few saying, they've ran into some new harnesses wired wrong there. Be something worth looking at.

 

[threewood]

Might be off base, but have you checked to see if the headlight switch plug is wired right? Think I remember a few saying, they've ran into some new harnesses wired wrong there. Be something worth looking at.

It is the old harness, but replaced connector. I checked the headlight wiring, the wiper wiring, the floor dimmer wiring, the dash dimmer wiring, ignition wiring, the hazard wiring and they are all correct.

I pulled the instrument circuit board ( fyi, it is much easier to remove the board from the back than to pull the cluster out the front) and fixed the broke pin, cleaned connections and checked all bulbs and sockets, tightened everything back on. Getting ready to put the main harness back in. I will keep all accessories unplugged and check the lights, then attach them one at a time.

 

[threewood]

I'm blaming Mexican Duralast on this one!!!

I got the harness put back in and it was still pulling juice with everything in the cabin unhooked except the geadlight switch. Started taking the front end apart thinking there is a fucky wire in the new harness. Low and behold there is a brass sleeve missing from the Duralast socket. I popped the bulb out and the spring was rubbing the socket!!! MFer!!!!! Everything works now, except maybe not the fuel and temp.....but that is another project.

On the positive side, I believe that harness pin was broke so it needed fixed anyway.

 

[threewood]

Back to square one. A few of the dash lights ( oil and brake) stopped working as well as the blower, windshield washer and the turn signals. Courtesy lights and dash lights work.

Now when I go to high beams it shorts out and the new high beam switch gets hot. Hazard lights work front and back and I swapped the buss flasher with turn signals and no change.