Blinker Troubleshooting Help Needed: 1974 Lincoln Mark IV

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My Lincoln
1974 Lincoln Mark IV
Hi everyone,

I recently acquired a unique find: a 1974 Lincoln Mark IV with only 48k miles on it. However, it had been sitting on the street for the past few years, and I’m gradually addressing the issues one by one. It’s a baby step process.

I’m currently facing some problems with the blinkers of my ’74 Lincoln Mark IV. The hazard lights are functioning correctly, but the blinkers aren’t. Here’s what I’ve checked so far:

- I replaced the flash relay for both the hazard and turn signals. The original relay for the blinker looked worn out, but I kept the original hazard relay, which is working fine.
- I’ve checked the fuses, but the 7.5 amp fuse for the cornering lights keeps blowing, and the lights don’t turn on.
- When I press the brake pedal with the blinker stalk engaged on the left, the brake lights turn off, but there’s no blinking. The same happens for the right turn.
- Using a voltmeter, I’ve noticed that there’s no reading from the contact going to the flash relay for the blinkers. It’s just random numbers. If I turn on the hazard lights, the voltage drops. I might have did not check correctly. I connected voltmeter leads to the two wires of the flasher instead of one and ground.

Additionally, the AC system doesn’t have a belt but is connected to the clutch. I thought to mention this because I understand that the positive wire for the blinkers shares power with the AC clutch.

I’d appreciate any insights or similar experiences you may have. Thanks in advance!

TLDR:

1974 Lincoln Mark IV Blinker Issue:
• Hazards work, blinkers don’t.
• Replaced flash relay, still no blinker function.
• Cornering light fuse keeps blowing.
• Stalk on the wheel disables brake light when engaged.
• No voltage to blinker relay.
• Lightbulbs are functional (corner bulbs unknown)
 
Just from general electrical troubleshooting, I think you have at least two problems to look for. One being a short with the cornering lamps and the other being a ground issue with the turn signal and/or brake lamps.

Diligent tracing of the wiring will be needed to trace the short. Thankfully, they do now make a relatively inexpensive tool to help locate wiring shorts. Search your local auto parts vendor to see if they have one in stock.

As for the ground issue(s), inspect each lamp socket assembly and pigtail carefully for proper grounding. Without a working ground circuit, one malfunction can wreak havoc across the entire lighting circuitry leading you chasing your tail tracking the seemingly unrelated symptoms.

I know neither suggestion is of great help but just hoping to point you in the right direction.
 
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