[CThunder-blue]

Originally Posted by InvisiBill

In this usage, "ground" is equivalent to "negative". DC like this just has a positive and negative (also commonly referred to as ground), unlike AC where there's a ground distinct from the hot and neutral.



They're even called "negative ground/earth" systems. The chassis is a ground specifically because it acts as a conductor in the negative half of the circuit.




That was the first part of my example. If you remove the negative first, and accidentally touch the wrench against metal while doing so, nothing happens because the negative is already connected to the metal (there's no difference in potential, aka voltage, because they're wired together). Then when you remove the positive, if you accidentally touch metal, nothing happens because you've already broken the circuit (the metal is no longer connected to the negative terminal of the battery).

If you remove the positive first and accidentally touch metal, you're grounding out the positive terminal directly through your wrench (i.e. completing the circuit between positive and negative). Since the negative terminal is wired to the chassis, touching the back of your wrench to the metal while trying to remove the positive is the equivalent of laying your wrench directly across both terminals of the battery.

Regardless of which terminal you start with, the circuit is equally broken after the first terminal is disconnected (making the second terminal "dead" while you're working on it). However, one way is much safer in case you do happen to slip while removing the first one. In an older "positive ground" vehicle, you'd want to disconnect the positive first to avoid accidentally shorting out the negative terminal against the positive chassis. It has nothing to do with which way the electrons flow, but with the physical layout of metal (which happens to be connected to the electrical system) around the terminals.


And getting back to the original topic of flashers, the EX500 guys have found that some off-brand EP34 "equivalents" (like the Blazer FL34) don't work properly with LEDs. As soon as they got an actual Tridon EP34, it worked exactly like it was supposed to. The LF1-S-FLAT from SuperBrightLEDs.com (as mentioned above by chone) is a PnP replacement on the later EX500 too, and has worked flawlessly for me with OEM bulbs and LED replacements. It's worth a couple extra bucks to me to be able to just plug it in, rather than taking the time to chop up my harness to match a generic flasher.

You're not saying anything different than what I'm saying, except how we differ on semantics. As far as old vehicles using positive ground systems, since the 250 isn't one, there's no point in bringing it up.

TLDR- just disconnect the negative side of the battery to avoid any unpleasant surprises.