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EFV-8 Club Forum / General Ford Discussion / Battery Cutoff Switch

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Posted By Discussion Topic: Battery Cutoff Switch     36fordor 06-15-2015 @ 5:01 AM reply profile send p.m. Member Posts: 78 Joined: Oct 2009 There's a battery cutoff switch advertised as a "12 Volt 300 Amp Battery Disconnect Cut Off Kill Switch". This looks like the common disconnect switch with the removable red plastic key. Would it make any difference, cause a problem if the car were 6 volt? Thanks. trjford8 06-15-2015 @ 6:34 AM reply profile send p.m. Senior Posts: 4214 Joined: Oct 2009 Those switches work on 6 or 12 volt. TomO 06-15-2015 @ 7:08 AM reply profile send p.m. Senior Posts: 7250 Joined: Oct 2009 I would look for a switch with more current capacity. The starter draws 200 amps and can draw as much as 500 amps on initial engagement. A switch with only 300 amp capacity will develop resistance when subjected to loads above its capacity. A good cutoff switch will not drop more than 0.1 volts when measured with one lead at the battery and the other lead on the load side of the switch while the starter is engaged and the ignition switch off. Make sure that you use 6 volt cables to and from the switch. Tom len47merc 06-15-2015 @ 8:25 AM reply profile send p.m. Senior Posts: 1165 Joined: Oct 2013 36fordor - I too looked at that switch and a host of others, but never found one I was satisfied with from performance, safety, aesthetic and/or originality perspectives. I definitely did not want to drill mounting holes in an original firewall or wheel well housing to mount a switch either. In the end it came down to, whether I had the switch or not, it still required opening the hood and walking around to the passenger side to perform some function to disconnect the battery. Since it is hardly any more effort to keep a 1/2" open-end directly beside that side of the car in the garage I have taken the advice from others on this forum, ditched the switch idea and simply remove the negative cable. Likely have performed this dozens upon dozens of times and the cable end shows no worse the wear. I know I am getting the best possible connection and the trouble to perform the disconnect and reconnect is hardly more than what a switch requires, and with some switches, no more or less. I have seen others, including at the recent Eastern Regional in Charlotte, with the battery-mount, round green knob switch (I can connect and disconnect about as fast as this switch) as well as cars with the switch you mentioned and yes as trjford8 states they all work, technically just none as well as a direct connection with the original cable. Opinions abound on them - some love the switches, others not so much, the purists and/or those with the preference for the best connection possible not at all. If you feel you must have one take TomO's advice, not only for performance but for long-term peace of mind. Steve flatheadfan 06-15-2015 @ 5:59 PM reply profile send p.m. Member Posts: 450 Joined: Oct 2009 I agree with others the simplest way to prevent an electrical flow is to disconnect a cable from the battery. However, things get cumbersome if your battery is under the floor such as found on pre-'37 models. What I have done to my '35 and '36 is to mount a cut-off switch under the hood. There was no need to drill any holes, I used available factory frame holes. It also makes for an easy hook-up for a battery tender. Tom len47merc 06-16-2015 @ 8:57 AM reply profile send p.m. Senior Posts: 1165 Joined: Oct 2013 Tom - I should have been more considerate of the pre-'37 owners & of course '36'fordor. Do you know what the amp rating is of the switch you are using (in the photo)? Steve MGG 06-16-2015 @ 12:00 PM reply profile send p.m. Member Posts: 85 Joined: Jul 2014 Question for TomO - Does the 0.1 voltage drop that you mentioned above apply to the switch regardless of wether it is hooked up to the negative hot post or the positive ground post of the battery? 1934 Ford 06-17-2015 @ 7:05 AM reply profile send p.m. Senior Posts: 573 Joined: Oct 2009 Both types work fine. But mount it inside the car so you can shut the battery off without having to get out and open the hood. Just in front of the seat is a good spot in the wood floor board for the orange one or with the metal one that flatheadfan pictured, in the frame rail just ahead of the seat. Down there they aren't to noticeable. 1934 Ford's since 1972 TomO 06-17-2015 @ 7:13 AM reply profile send p.m. Senior Posts: 7250 Joined: Oct 2009 It does not make a difference which post has the switch. The 0.1V measurement is a reflection of the resistance in the circuit with 150 amp draw by the starter. It represents about .0007 ohms resistance, which is very hard to read with an ohm meter. Tom

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