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Old 09-28-2008, 12:08 PM   #1 (permalink)
It smells funny in here.
Join Date: Sep 2008
Location: Southern Wisconsin
Posts: 63

GeeOh - '97 Geo Metro Base
90 day: 33.41 mpg (US)
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Battery drained overnight after install of tach on '97 metro. Advice?

I'm completely stumped on this one. Installed a cheezy Sunpro tach and a vacuum gauge last night. Drove around for a bit. All good.

This morning when I went down to start it, I got the dreaded click. Took a bunch of plastic apart again to verify my connections, and I don't see any problem.

The tach is 4 wires, Red, Green, White and Black. Black is ground, I took that right to the battery. Green is signal, that's going to coil negative, the Brown/White wire. Red is switched power, supposed to be hot in run only. After perusing the schematics in Chilton's, I chose to take it to the rear defogger circuit, since it was right there and easy to grab. Per the manual, and verified this morning with my meter, that line, Yellow/Green coming into the switch, is only live when in run or start. White wire is for instrument light/dimmer. I took it to one of the two hot wires on the instrument dimmer switch. I believe it was the Orange/Green. Lights on the gauges are not dimming with the OEM panel, but they are also not on when the headlights are off, so that should not be causing my problem. Verified with meter.

Wiring on the vac guage is just a hot and ground for a single bulb, and I have those spliced to the white and black wires from the tach.

So... where the heck did my juice go overnight? It's a brand new battery, which not only pretty much rules that out as the failure point but really ticks me off to be deep-discharging it like this right away. Darned things aren't cheap.

The only other thing I can think of is a high-resistance short somewhere, not enough to pop a breaker but still drawing current. Thing is, I really wasn't into all that much to install this, and I triple checked all the connections this morning and saw no issues. I do have a couple of lame butt-crimped splices, but they are solid and clean. Or as solid and clean as such a connection can be, anyway. I would normally have soldered and heat-shrunk, but it was late and I was being lazy. The rest of the connections are those inline snap and splice thingies. In any case, none of those points are hot with the key and headlights off.

After charging it up this morning and checking all those other connections, I verified that the charging system in the car was fine. Then I shut it down and have been checking the battery voltage periodically since then. It has only been about an hour, but it settled down to about 12.75v and seems to be staying there so far. Using an inductive meter on the + cable, I'm not reading any amperage draw at all out of the battery with the car shut down.

I would not be obsessing over this at this point, but I am pretty certain I didn't leave anything else on, and nothing is more freaking irritating than battery that konks out unpredictably.

Sorry for the longwinded post, but I wanted to make it clear that I have checked everything I know to check. And still have no idea!

Can anyone offer a hint?

Last edited by lyd; 09-28-2008 at 12:23 PM..
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