I have installed a new wiring harness and converted to 12 volt negative ground. I have also replaced the vacuum wipers with electric and the original radio was converted to AM/FM. I’ve had two people tell me not to hook direct to the ignition switch but to go through a relay. Naturally they did not explain how. Can anyone describe or sketch how to do this? Also where and what to buy. Thanks in advance for the replies.
how old are those two people who told you to use relays? just curious....most modern cars have relays to power a lot of things, but old cars don't, because they really aren't needed. The wiring harness you got was designed to power those things without relays, so it should work fine, and eliminate unnecessary work, if you just ignore the folks telling you to use relays. But also, don't connect directly to the ignition switch. Instead, use the fused wires that are there just for those things, in the new harness. Did you look and see if it has a RADIO and a WIPER fuse, and wires labeled for them?
What kit did you get? Did you lose the instructions? What is the main question? Hooking up the radio? Get the main engine wired. Get the main ignition switch wired. Then lights front and rear. Then accessories. as Squirrel said. Check for the wire labels. If you wires are not labeled. Maybe too cheap of a kit? find a basic diagram for you car and follow it.
here's a thread from the barn. on page 2 a schematic that makes your switch a ground to trigger the relay. https://www.fordbarn.com/forum/showthread.php?t=256654&page=2
my post above is meant for stock harness, and stock switch. the point is the old ford switch plate was not made for a lot of amps.
As I was reading this thread I was wondering if the reason for suggesting relays was to reduce the load on the original ignition switch. When I rewired my '50 last winter I used all (most) of the original dash switches and ignition switch. I used relays to take the load away from the ignition switch and headlight switch. I'm not really running a lot thru the ignition switch, but the radio is wired through the switch. The radio I use is more modern and not a big current draw. I'm not sure how much current your radio draws, perhaps a relay might be a good idea. I used bosch style relays ( 40 amp relays are easy to get and will handle most loads you need) Wiring information often come with the relays but if not the internet can show you how to wire them in.
Many modern radios use two power connections. One is on full time, and it is the one that draws the majority of power for the radio. The other is only on when the key is on, and it's just a signal wire, to let the radio know that you want it turned on. You can usually tell by the size of the wires, which one is going to draw the most current.
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