Automotive turn flasher wiring relay

Thread Starter

luiscr

Joined May 25, 2019
10
Hi,

I'm currently repairing an old Ford tractor, and i've got a doubt about how to wire the turn indicator lights.

The tractor has 2 pair of 21W 12V lights, so when the turn switch is on, 2 x 21W lights are on.
I've bought a 3 pin flasher relay for this effect. My question is if I can wire the bulbs directly to this relay, or if I should use a 5 pin automotive relay to power the bulbs.

flasher relay.jpg flasher2.jpeg

Thanks in advance!
 

Reloadron

Joined Jan 15, 2015
5,934
The flasher module should have the three prongs labeled X, L and P where X is the battery power, L is the load switched to Left or Right lamps and P is for a Pilot lamp when used to let you know a turn signal is on. You should not need another relay as most will drive the lamps direct. The maximum (and minimum) current should be on the flasher module. Some use current and others power (watts).

Ron
 

Thread Starter

luiscr

Joined May 25, 2019
10
The flasher module should have the three prongs labeled X, L and P where X is the battery power, L is the load switched to Left or Right lamps and P is for a Pilot lamp when used to let you know a turn signal is on. You should not need another relay as most will drive the lamps direct. The maximum (and minimum) current should be on the flasher module. Some use current and others power (watts).

Ron
Thanks for your reply!

Shouldn't one the prongs be connected to ground?

I thought that in these 3 pin relays one of the prongs should be connected to 12v battery, another to ground and the third to the positive end of the bulbs.

IMG_20210131_230946.jpg
Here is a photo of the relay.
 

Reloadron

Joined Jan 15, 2015
5,934
The lamps are normally grounded at their bases. Here is one such example. That said not all automotive flasher circuits are created equal. Most older units are actually a thermal switch where the load current heats a bi metallic switch opening and closing a set of contacts. This type does not require a Ground, ground is made through the lamps. This is also the type which switch faster when a front or rear lamp opens (burns out) because the load has changed the switching rate changes. This would also be what we find on old tractors and farm equipment.

So if you have lamps grounded to the tractor frame you are only doing high side switching. There is no need for a ground on the flasher unit. Newer stuff, especially stuff using LED lighting uses a totally different electronic scheme. There are also 3 prong flashers which do use a Ground pin rather than a P (Pilot) pin so it depends on what you have or want.

Ron
 

Thread Starter

luiscr

Joined May 25, 2019
10
The lamps are normally grounded at their bases. Here is one such example. That said not all automotive flasher circuits are created equal. Most older units are actually a thermal switch where the load current heats a bi metallic switch opening and closing a set of contacts. This type does not require a Ground, ground is made through the lamps. This is also the type which switch faster when a front or rear lamp opens (burns out) because the load has changed the switching rate changes. This would also be what we find on old tractors and farm equipment.

So if you have lamps grounded to the tractor frame you are only doing high side switching. There is no need for a ground on the flasher unit. Newer stuff, especially stuff using LED lighting uses a totally different electronic scheme. There are also 3 prong flashers which do use a Ground pin rather than a P (Pilot) pin so it depends on what you have or want.

Ron
Thanks for such a good reply.

Now I understand why I managed to blow 2x 7,5A fuses today, and the relay itself twice xD

I didn't think clearly on this before making the connection. Know thinking clearer, what I didn't didn't make much sense because I knew that the amount of watts being consumed would interfere with the relay's clicking time (so that when 1 lamp blows, the clicking is faster), and the way I was connecting the prongs was independent of the bulbs.

I now have to buy a new relay and then i'll give you feedback.

Thanks once again!
 

Thread Starter

luiscr

Joined May 25, 2019
10
What i'm understanding is that there are many different types of flasher relays.

http://www.derek.com.au/flasher.html

Unfortunately I can't find much information about the relay I bought, but according to this link, it looks like my relay may be the type that Reloadron suggested.

I tried connecting the relay such as shown in this youtube video, but I shorted 2 fuses and the relay, so I'm quite sure Reloadron may be right on this specific relay.
 
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