this is a weird one.... lighting question.

[Gman73]

Guys,
on my 73 k 20 I've got the dash removed no gauges etc. I do have my fuse block and all my wiring intact. So issue is when I pull my headlight switch out I get headlights all the running lights, brake lights and one turn signal left side rear, no other turn signals. How would I trace this back to find the issue? I'm guessing fuse block somewhere as it's pretty crusty. Also how hard would it be to replace that fuse block with a modern one?

 

[Vbb199]

The back right side not working I think is just a plug near the tag, behind the bumper. It carrys power from the left turn signal side over to the right side.

The front turn signals could be the harness itself not properly grounded, a break in the wire, and/or just burnt out bulbs?

 

[Vbb199]

Yea. Here's one on my 79 c10.

Presumably it's close to the same on a 73.

You must be registered for see images attach

 

[dvdswan]

Check for dirty grounds on the for each light.

 

[sirweesarunch]

Grounds are bad. Put a test light on the contacts securely ground and see if its got 12 V.

 

[Randy and Easton]

☝

 

[Grit dog]

What they said….
I’d start cleaning up grounds at the problem areas. Each tail light has its own ground to the body.
Then move to tracing + power to anything not lighting up like vbb suggested.
Do the turn signals work at all/otherwise? Or are you just saying they come on with the running lights when they shouldn’t?

 

[Gman73]

I have power to all the lights they all come on, only the left taillight blinks

 

[Grit dog]

If the blinker is actually blinking and turn signal is not on, seems like an issue up front? I’d still clean the grounds at the lights and inspect wires and plugs because it’s easy
Do turn signals work otherwise? Running lights on or off.

 

[rich weyand]

Make sure cab is grounded to engine (firewall to RHS cylinder head), engine is grounded to battery (the heavy wire), and battery is also grounded to frame (light wire to the radiator crossmember). If they don't all agree on what 0 volts is, weird things happen.

 

[AuroraGirl]

Make sure cab is grounded to engine (firewall to RHS cylinder head), engine is grounded to battery (the heavy wire), and battery is also grounded to frame (light wire to the radiator crossmember). If they don't all agree on what 0 volts is, weird things happen.

Isnt there a stock fender to battery connection? Or perhaps that was to frame? or it existed on mine and I made it better at one time for fun lol!

 

[WP29P4A]

I just reread your first post. It says that when you pull the headlight switch out the running lights and the brake lights come on. Is this a typo? or is this correct?

One of the other causes of issues like this are people who don't pay attention and inadvertently replace dual filament bulbs with a single filament bulb. Verifying the brake light bulbs and the turn signal bulbs are correct will quickly cross one more item off your list. I have also seen trailer wiring create similar issues.