LED Question

quote:

The question is; would there be enough drop with the incandescent lamps on to pull the battery voltage (about 10 vdc) down enough to not trigger the leds?

In a word, yes. LEDs have a very narrow voltage window in which they operate.

If you measured that 10 vdc at the battery, then you either need to charge the battery, or your battery is going South.

If that 10 vdc was measured at the third brake light, then you appear to have a significant voltage drop in your wiring, possibly caused by a bad/corroded connection or a brake light switch with high internal resistance. This assumes that the battery voltage is at least in the mid 12 vdc (or higher) range. IMHO

John

Thanks, I thought it might be something like that. The car has been sitting with doors open and interior light on. I think the battery is OK, just discharged some and will come back when run awhile.

Glad to help. You might consider adding a quick disconnect switch at the battery. That way you can keep from draining the battery when working on the car with the doors open, or when something goes wrong (electrically), you won't waste time searching for a wrench to disconnect the battery.

John