The Ford Barn

PGBuick · 12-09-2023, 12:29 PM

I’m building the wiring harness for my 36 coupe, which is 12 V negative ground. Stock flathead powered, power-master alternator and starter, and electric fan via a fan relay. Headlights TBD. Also an under-dash Arvin heater with 12v fan. I’m guessing with 12v power my current draw across the stock on/off column drop switch won’t be a problem, but figured I would ask those who have been down this path before. I know I can add relays and or an additional master on/off switch for devices powered by “ignition” (aka not constant 12v) power, but it’s simpler to just put them all through the stock switch if it’s robust enough. And simpler is always better.
Thanks!
Pat

richard crow · 12-09-2023, 01:08 PM

install a relay operated by the collum switch

cas3 · 12-09-2023, 01:15 PM

When I made my harness I had similar concerns as you. So, I got a simple 4 fuse panel from ebay, and used a relay to trigger it from the stock switch. The diagram is here on the barn if you search. On mine, I ground the IGN switch, to trigger the relay. This is for heater fan, cig lighter socket, and radio.

oldbugger · 12-09-2023, 01:19 PM

Stock switch is not robust enough, let it power a relay, as said above.

Terry,OH · 12-11-2023, 08:18 AM

It is not so much the current alone that does damage to contacts but the wattage. The watts are V x I The original switch is most likely good for about 40-45 watts peak and only carries about 30. W continuous.

Gene1949 · 12-11-2023, 09:02 AM

Sponsored Links (Register now to hide all advertisements)

I "repurposed" an entire wiring harness and relay/fuse box from a Ford Ranger pickup. The indash switches only function is pilot duty for the relays.

12-09-2023, 12:29 PM	#1
PGBuick Member Join Date: Nov 2021 Location: Central Mass. Posts: 96	Max. safe current draw across stock 36 Ford ignition/ on-off switch? I’m building the wiring harness for my 36 coupe, which is 12 V negative ground. Stock flathead powered, power-master alternator and starter, and electric fan via a fan relay. Headlights TBD. Also an under-dash Arvin heater with 12v fan. I’m guessing with 12v power my current draw across the stock on/off column drop switch won’t be a problem, but figured I would ask those who have been down this path before. I know I can add relays and or an additional master on/off switch for devices powered by “ignition” (aka not constant 12v) power, but it’s simpler to just put them all through the stock switch if it’s robust enough. And simpler is always better. Thanks! Pat

12-09-2023, 01:08 PM	#2
richard crow Senior Member Join Date: May 2010 Posts: 1,770	Re: Max. safe current draw across stock 36 Ford ignition/ on-off switch? install a relay operated by the collum switch

12-09-2023, 01:15 PM	#3
cas3 Senior Member Join Date: Jan 2011 Location: sw minnesota Posts: 4,578	Re: Max. safe current draw across stock 36 Ford ignition/ on-off switch? When I made my harness I had similar concerns as you. So, I got a simple 4 fuse panel from ebay, and used a relay to trigger it from the stock switch. The diagram is here on the barn if you search. On mine, I ground the IGN switch, to trigger the relay. This is for heater fan, cig lighter socket, and radio.

12-09-2023, 01:19 PM	#4
oldbugger Senior Member Join Date: May 2010 Location: Holland Mi Posts: 642	Re: Max. safe current draw across stock 36 Ford ignition/ on-off switch? Stock switch is not robust enough, let it power a relay, as said above.

12-11-2023, 08:18 AM	#5
Terry,OH Senior Member Join Date: May 2010 Posts: 4,751	Re: Max. safe current draw across stock 36 Ford ignition/ on-off switch? It is not so much the current alone that does damage to contacts but the wattage. The watts are V x I The original switch is most likely good for about 40-45 watts peak and only carries about 30. W continuous.

12-11-2023, 09:02 AM	#6
Gene1949 Senior Member Join Date: Jun 2016 Location: Pahrump, NV Posts: 374	Re: Max. safe current draw across stock 36 Ford ignition/ on-off switch? Sponsored Links (Register now to hide all advertisements) I "repurposed" an entire wiring harness and relay/fuse box from a Ford Ranger pickup. The indash switches only function is pilot duty for the relays.