67 F100 Brake Light Wiring / Electrical Question

[clineco]

Hi All -

I'm not sure what's wrong with my wiring, but my brake lights are not working. The primary thing I notice is this:

At the brake light switch...when the wires are disconnected from the switch I have power to the Red wire. I also have continuity from the Red wire w/ Black stripe back to the Right and left tail lights.

The problem is that when I hook up the 2 wires to the brake light switch or manually connect them, I lose power in the circuit, it goes completely dead. But when I disconnect the wires I regain power in the red wire.

all other lights and signals work fine, I just don't know enough about electricity to know why the circuit would go dead when it is hooked up.

I did check the bulbs and also the switch itself and they seem to be fine.

Thoughts?

[sargentrs]

That's just weird. Replaced brake light switch? You have power in. The switch is just a contact. With the button pushed you should have continuity to both pins. Then power out to the brake lights.

[UKPR1]

Clinco,

As unanalytical as it sounds...jiggle the turn signal arm as you're applying the brakes and have someone see if they operate then, albeit intermittently. Worked for me and told me my turn signal - or at least various contacts within that turn signal - weren't doing their job. Power to the brake lights comes from the turn signal. Other than that - make sure contacts on the stop light switch/pigtail are clean and corrosion free. I just got my reverse lights working after a week of trying far more complex solutions.

Geoff

[zgerbic]

Clineco,

I think I agree with UKPR1 that there is corrosion causing the problem. What you are seeing at the brake light switch is to be expected when there is corrosion between the battery/power and the brake light connector. Why you see it is that corrosion is like having a high value resistor in the circuit between the battery and the connector. The voltmeter will detect 12V because it draws so little current (maybe .0001 amps) that there is no voltage drop across the "resistor". When you connect the brake light wire (810), the current draw is several amps, causing the corrosion "resistor" to drop almost all the 12 volts. Corrosion in older vehicles is a common problem and can occur anywhere there are metal to metal connections, especially switches.

The turn signal switch is between the brake light switch and the brake light bulbs.

Remove the brake connector and connect battery power directly to the wire going to the turn signal switch which should direct it back to the brake lights (810). They should come on. If powering the 810 wire with 12V does not make the brake lights work, the problem is probably in the turn signal switch. If powering 810 does not work, the problem is in the wiring back to the fuse block along wire 284.

Power to the brake light switch is wire 284 which goes to a 20A fuse. The corrosion is most likely in the fuse connections or the fuse connection to the 284 wire. The Emergency flasher circuit may also not be working. Does yours work? It gets its power from the same fuse/connections. I had some strange intermittent problems with my gauges because of corrosion on the fuses.

Regards