Hi all,
I want to install a battery disconnect switch from my battery to the cab of my 1990 W250, about 6'. What size wire should I use?

 

The bigger the better. If it will be the main power or ground, I'd go with 4 gauge or bigger. 2 gauge ought to be more than plenty.

 

You can get terminals with them.

 

The idea for a battery disconnect in the cab is so I don't have to open the hood to disconnect the battery which I have to do because I have a short somewhere in my electrical system that drains the battery in a few days if I'm not using the truck. I don't know how to find the short or whatever it is that's draining the battery. The springs on the hood are way under powered which make it rather heavy for this old man.

 

finding a short is relatively easy if it is a stock circuit. remove negative wire from battery. put test light between ground cable and ground terminal and start pulling fuses out of the fuse block till light goes out.

 

I put the test bulb between Pos and Neg posts to make sure it lights, then between Neg post and Neg cable. No light. Does that mean there's no short or the moon's in the wrong phase? Maybe it's Obama's fault. I have a wing nut battery clamp on the Neg battery terminal and a side terminal post clamped in the Neg cable with a 4" piece of flattened copper pipe bolted to it and a hole drilled in the other end that connects to the wing nut post to make it easy to disconnect the battery. Sometimes when I reconnect the battery I get a spark. Other times not. When I disconnect the battery I attach a trickle charge unit on it so the battery stays fully charged. I suppose I could leave the trickle charger off for a week and see if the battery discharges even when not connected to anything. If I had heavier / stronger springs on the hood and could figure out how to put them on I probably wouldn't bother doing all this.
Thinking about going with 1AWG welding cable for the disconnect. Read it's good for 250 amps. Don't know the amp draw on starting or running. Only going 6' or less each way coming off the engine to the disconnect switch in the cab then back to the battery.

 

if the light stays off when between ground wire and terminal then there is no short. might just have a week battery. they get old and start discharging even if they are not hooked up. have you had the battery checked to make sure it is still good?

 

I would disconnect the alternator lead first in this test. There are diodes in there and if one is bad it will drain the battery.

 

6 days since battery was disconnected. Tested 12.79amps. When I drove it regularly it was fine. It was only after it sat for 4 days or longer that it wouldn't start. There's a battery drain somewhere. But this vid is a good thing to know. Thanks.

 

Back to this. If the battery cables ( look to be ) are 4/0, is it wise to replace one for the disconnect switch with a 1 or 2 gauge AWS cable as suggested above by ol' grouch? Why then are the stock cables so big? I'm only cranking the engine over for 4 sec. or less to start my truck.