In order to keep your radio presets in place, I understand you can jump across a battery disconnect switch like the one I just installed. Does this simply involve running a fused wire from the terminal to bypass the disconnect switch? If so, what ampherage should the fuse be, and will you blow the fuse if you try to start the car without engaging the switch (I tend to forget things these days)?

JB

'78SA

 

Yes, in fact you can buy them that way - with a little fused wire already attached. I got one of those and removed the wire, since my clock doesnt work and I have no use for it.

I tend to forget things also, like what amp fuse is in there! Looks pretty small. Seems likely it would blow. You will have to try it!


oh well, one out of three aint bad... MJ

 

Mark,

Where did you get the switch with fused bypass? I ordered one from Eckler's, but it seems it's just a plain switch...

Thanks,
-Pedro

 

Yes. all you need to do is run the wire from one part of the batt disconnect to the other. Mine came with a 30a fuse, but just about anything less will still work well. Clocks and radio presets don't need a lot af amps to work. I have had mine for a month and blown it twice because I keep forgeting It's turned off.:bb For some reason, the 30a just isn't enough to turn the starter :D

 

I tend to forget things also....

Probably it was the only one they had at the local autoparts store, because it costs a little more for the fused wire, and I don't need it. MJ

 

Thanks, Mark! Somehow this thing is not that easy to find here in my area... Had only gotten head-scratching when I ask for one at the parts stores, and the only one I found was for side terminals, and wouldn't work for me. That's why I had to order one...

-Pedro

 

Thanks, guys. Something else has occured to me, though. The main reason I bought the disconnect was because I'm worried about the old wiring grounding out somewhere, heating up and causing a fire. If I put that 30amp bypass in for the radio & clock, will that be enough juice to maybe start a fire if a wire grounds out? That's probably a stupid question, but I'm pretty electrically ignorant. :confused:

JB

'78SA

 

They sell one with bypass.

 

(emphasis added by me - MJ)

I have asked that question several times for the exact same reason! Have not received a definitive answer. I now have a Sears security battery in the vette. When I turn the battery off with the remote it will start the car but then stall in 3 seconds. Same question: When the battery is in "security mode" does it provide protection from electrical fires? I dont know, but I usually turn the battery entirely off. This is accomplished by pressing a button on the battery itself. Anyway, as it relates to a battery cutoff switch, I think this is a very important question and I do not know the answer! MJ

 

you only really need about a 5 amp fuse for the bypass. the radio presets only use somewhere in the milliamp range, but when you open your door the interior lights will blow a fuse rated too small. 5 amps should be more than enough

 

Seems to me that bypassing the dissconnect switch defeats the whole purpose. Why are you disconnecting the battery? If you're disconnecting the battery because it's dying, then you need to fix the short. If you're disconnecting it for winter storage, well thats not working because its bypassed with a fused link. The battery is still getting a current draw, and you're going to blow the fuse if you do something that requires too much power, like start the car or even open the doors. The winter storage solution would be one of those 9V battery deals that plug into the cig lighter to keep the radio settings.

I have a disconnect in my vette because im working on it all the time, and i'm lazy to wrench off the terminal. One quick turn and the juice is turned off for the whole car.

It seems to me that bypassing the dissconnect does not disconnect the battery, and only blows a fuse if you ask too much from it.

If you must bypass the switch, then ohms law rules. Voltage = Current * Resistance. you can measure the resistance of everything you need to do across the positive and neg battery wires. (battery out of the picture and everything you want on) The current reguirement will be 12V divided by the measured resistance. For instance, if 2.4 ohms is measured, then 12 / 2.4 is 5 amps. You would probably select a 10 amp fuse for this application.

Of course even this would be rediculus, normal current draw off a battery with the car off is about 5 millli amps, thats 2.4K ohms seen by the battery.

Jim-K :seeya

 

Jim, you underestimate how ignorant I am. That's all so much Chinese to me. I get that you're saying that jumping the disconnect defeats the purpose, at least to an extent. But what I'm still not clear on is whether 30amp or even 5amp is enough to start a fire somewhere if you have a short in the wiring.

JB

 

I'm assuming you're using an aftermarket radio with electronic presets. Most of these radios have a dedicated electrical connection for this purpose. They usually already the proper fuses built into the wiring harness for the radio.

If you do have the dedicated wire, run a wire from the battery directly here.

In a modern car the most draw you should see when everything is turned off is about 300mA.

I highly doubt 30amps would be sufficent to start a fire. If you're concerned about something shorting out while the car is parked, you really should be more concerned while driving. While driving all the wires are subjected to shock.

 

Gerry, I am concerned about it driving, too, which is why I keep that big honkin' fire extinguisher strapped down the back.

I'm even more worried, though, about something happening in the middle of the night while the thing's parked in my garage. There was a thread a couple months back about somebody losing his car & his garage that way. Don't want my house burning down around my ears while I'm asleep. If a 5amp fused bypass will keep the radio presets and still prevent that from happening, I'll be happy camper.

Thanks for the tip about the dedicated wire on the radio--I'll look for that, though it wouldn't help me with the clock if my clock worked. But it don't, so cool. :D

JB


[Modified by JB, 12:43 PM 8/21/2001]