An Open Letter to those who contemplate working under the dash to find a power source...
02-10-2004, 06:24 AM
#1
AudiWorld Super User
Thread Starter
An Open Letter to those who contemplate working under the dash to find a power source...
This note is prompted by the frantic HELP request late last night from Mark3.2TT.
OK, everybody makes mistakes. Personally, I have done this also, that is, arc a tool across a heavy power source to ground. Once.
Please consider this as you work on your cars.
Please keep this picture and text for reference.
<img src="http://ttbipes.home.comcast.net/jpgs/12vterminals.jpg">
Look at the 4 terminal lugs. I show them here for reference. You can use these to see where you can tap in for the +12 V, but you need to be very careful if you do. These lugs are buss terminal feeds from the battery, to the fuse box. They are LIVE +12V. If you tap into one of these posts, be sure you use an in-line fuse to your add-on device. The yellow lug at the left is "switched". Keep the lead as short as possible, from the fuse holder to these lugs. In fact, I DO NOT recommend that you tap in here, if you are at all concerned about doing this. If you do not fuse a circuit coming from this area, you run the risk of melting a wire, and starting a fire. These terminals are 30 amps or more. Any small gauge wire coming from these posts, and reaching ground, will immediately heat up, and become red hot like the coil heater in an electric oven. This will happen way before a fuseable strip will blow, if at all. Also, look closely at this pic, on the left. I added in the fuse, (transparent holder) on the left into a fused circuit to run my radar detector.
You also run the risk of blowing relays, and starting a fire.
DISCONNECT THE BATTERY (NEGATIVE TERMINAL) BEFORE YOU WORK ON THESE POWER POSTS, PLEASE!
OK, everybody makes mistakes. Personally, I have done this also, that is, arc a tool across a heavy power source to ground. Once.
Please consider this as you work on your cars.
Please keep this picture and text for reference.
<img src="http://ttbipes.home.comcast.net/jpgs/12vterminals.jpg">
Look at the 4 terminal lugs. I show them here for reference. You can use these to see where you can tap in for the +12 V, but you need to be very careful if you do. These lugs are buss terminal feeds from the battery, to the fuse box. They are LIVE +12V. If you tap into one of these posts, be sure you use an in-line fuse to your add-on device. The yellow lug at the left is "switched". Keep the lead as short as possible, from the fuse holder to these lugs. In fact, I DO NOT recommend that you tap in here, if you are at all concerned about doing this. If you do not fuse a circuit coming from this area, you run the risk of melting a wire, and starting a fire. These terminals are 30 amps or more. Any small gauge wire coming from these posts, and reaching ground, will immediately heat up, and become red hot like the coil heater in an electric oven. This will happen way before a fuseable strip will blow, if at all. Also, look closely at this pic, on the left. I added in the fuse, (transparent holder) on the left into a fused circuit to run my radar detector.
You also run the risk of blowing relays, and starting a fire.
DISCONNECT THE BATTERY (NEGATIVE TERMINAL) BEFORE YOU WORK ON THESE POWER POSTS, PLEASE!
02-10-2004, 06:52 AM
#2
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great post, jeff! thanks.
i never would have had the nerve to try to wire things without your help, and i certainly wouldn't have known what i was doing otherwise.
i imagine that i would have either fried my car or myself.
so, again, thanks a lot!!
i imagine that i would have either fried my car or myself.
so, again, thanks a lot!!
02-10-2004, 11:49 AM
#6
AudiWorld Super User
Thread Starter
thank you. 2 recent incidents have prompted this, one here, one in the MNAudi grp...
a guy fried a relay on his A4 doing this same thing.
part was $35, and it took a day to figure out what the problem was.
On the A4, there are no real fuses like on the TT. The relay acted like a fuse, turing the relay cube into a maraca. (IT rattles)
part was $35, and it took a day to figure out what the problem was.
On the A4, there are no real fuses like on the TT. The relay acted like a fuse, turing the relay cube into a maraca. (IT rattles)
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