Tachometer draining battery?

[renobdarb]

I have a slow battery leak that I traced to fuse #7, which is one of the accessory fuses on the '78. I have my tachometer wired to it. When tracing the drain, I found that when I took out the #7 fuse the draw dropped from .09 amps to .01. I put the fuse back in, took a reading - which was back up to .09 amps - and unplugged the tach from the fuse, and again the draw dropped to .01 amps.

Could the tach possibly be causing this battery draw? It doesn't make a lot of sense, however I'm no electrical guy, so maybe someone can tell me if this is possible and/or what's happening.

[sped372]

If you unplugged the tach and your amp draw dropped then it has to be the culprit. Is that fuse always hot (even with the ignition off)? The tach shouldn't need power all the time, just when the engine's running - you could wire it to a switched fuse to fix the battery drain.

[renobdarb]

If you unplugged the tach and your amp draw dropped then it has to be the culprit. Is that fuse always hot (even with the ignition off)? The tach shouldn't need power all the time, just when the engine's running - you could wire it to a switched fuse to fix the battery drain.

That's a good question; I'm not sure if it's a hot fuse. How do I tell?

[sped372]

Got a test light?



Attach the clip to ground and touch either the metal part of the fuse, or the terminal holding it, with the point. If the test light glows with the ignition off you know the circuit is always hot. You could also use a voltmeter... if you have voltage between the fuse and ground with the key off, same situation. Make sense?

[dtrumbo]

If your '78 is still wired as the factory intended then fuse #7 is hot all the time. Perhaps fuse #12 would be the better choice as it's switched power.

[renobdarb]

If your '78 is still wired as the factory intended then fuse #7 is hot all the time. Perhaps fuse #12 would be the better choice as it's switched power.

I re-wired the tach to fuse #12, and that seemed to do the trick. Thanks for the tips, guys. The current draw dropped from .08 amp to .01, and I traced that leftover .01 amp to fuse #8, which is where my stereo is wired, so I'm thinking that .01 amp draw is just the memory on the stereo.

Anyway, no more battery drain is certainly a good thing!