The Stovebolt Site Forums The Shop Area The Electrical Bay 2 prong/ 3 prong signal flashers

My truck has a really old and really cool, period-looking, signal switch. It has an indicator light on the switch. It is currently wired into the truck’s mostly original (cobbled-up) wiring with a 3 prong flasher. Works good.

A re-wire is on the to-do list and I need to quit putting it off. Most of your universal wiring harnesses are set up with a two prong flasher. As I understand it, I could wire my old switch to a 2 prong flasher, but I would lose my “on-switch” indicator light (just don’t wire it in). And supposedly, wiring that indicator terminal to the two prong flasher is problematic because it will backfeed and mess things up….so the internet tells me.

1) Are my assumptions about the reaction of the signal indicator light correct?

2) If the answer to #1 is correct, it seems to me that the back-feeding problem could be remedied with a strategically located diode or two. Need to sketch it out, but it sure seems like that would work. Am I nuts?

If I understand your questions correctly, the answer to the first question is yes, I think so. The answer to the second question is possibly...hard to say for certain but many people seem to be. But, yes strategically located diodes might solve the back-feeding problem. Is there a reason you would not use the 3 prong flasher?

That depends on how the signal indicator light works. You might be able to modify the circuit to work with a 2 prong flasher. Why not modify the circuit to work with a 3 prong flasher? Wouldn't that be simply replacing the 2 prong flasher socket with a 3 prong flasher socket? There was a discussion on modifying a circuit to use an older signal switch awhile back. 23 pages is nuts and I'm not sure what the solution was.

https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1539841/1

That thread that Walter linked to was about how to use an older turn signal switch that needed separate rear bulbs from the brake lights. Probably not appropriate here.

I agree that changing out the flasher socket to a 3 prong would be the easiest solution. The third prong for the indicator light is isolated inside the flasher, so it would be easier than messing around with a diode.

I previously assumed the socket modification would be a PITA with one of these universal harnesses. They look kinda “built in” when viewing the photos.

I don’t have such a harness in front of me to study what all that might take. Might be easy peasy.

My simple brain envisions the diode modification as not being all that much trouble. You’d have two wires are fed from the flasher prong of the two prong flasher. The one of those two wires that routes to the signal indicator light….has a simple diode in it.

Perhaps it’s not QUITE that simple. I’m not an electrical technician.

The flasher can put out a flash signal to any and all bulbs. Including the one inside the column unit. Depending on the model of column unit and the harness part number. Need to have that info.

It would be easier for you to use/add an "in line" 3 prong if the harness does not use one.

With a 2 prong you can tap into the left and right front turn signal wires to supply flash to the pilot wire of the column unit.
Some harness kits have wires for dash mounted turn indicators, left and right. These can be utilized for a column switch pilot I think.

I can't remember what all I've done in the past anymore. But drawing from what I can remember and logic.

Logic...AKA...educated guess.....waiting for a guinea pig.....test.

The new 21 circuit wiring harness I installed only had 2 two prong flashers. One for signals and one for hazards. Since I was starting from scratch, I found a simple motorcycle turn indicator diode pack to use for incandescents and wired one pack into the 7 wire turn switch(which has a built in hazard switch), and one pack into an added bulb affixed to the speedo cluster. I have brights and turn indicators at dash level. Only using one flasher plug on the new fuse block. If you are re-wiring anyway, and aren’t afraid of trying it, it’ll make a clean install. Just have to triple check your wiring before heat up.

Bart/ Chip:

Good ideas. Sounds like there is a way to do it, just have to decide which way works best. I had wondered about doing the mod inside the switch itself. Been a while since I’ve had it open, but I think there is probably room in there.

Why not run a wire from the 3 prong flasher to the switch like it is wired now. Or if your dash has places for ind. lights they will be wired in the new harness.
The 3 prong flasher uses the same pigtail as sealed beam headlights.

George

George, there is no problem with a three prong. The "P" is for Pilot, which is for an "indicator" bulb. We have all advised that the easiest way is to use a three prong. Just brainstorming how to use a 2 prong.

He mentions that the current 3 prong works.

May want to use a 2 prong but worried about "feedback". I don't know of any feedback issue. Only is someone's theory. There are two types of flashers, "electronic" and "mechanical". The feedback stories may be coming from electrinic/LED cases. He will use only a mechanical/bi-metal flasher. The flash signal goes to and thru a bulb.... to ground. No feedback.

I laid out a piece of cardboard big enough to cover a bed(sleeping, not hauling)and measured the truck dash and where I was putting the new fuse block. Sharpied onto the cardboard a simulated diagram. Placed all the parts and divided the wires to the parts or exit out the firewall. Made connectors and cloth taped the whole thing. Drug the entirety out to the shop and slowly installed, making sure to wrap the gauges in towels to protect. It worked fantastic.

A two prong flasher would work fine if you have a right and left indicator in the dash. Just splice those into the appropriate turn signal output. That's the way most modern vehicles work.

But with an old turn signal switch with indicator (see attached pic), the 3 prong with pilot circuit would be best.

Clean install, Chip. What you got there where the voltage regulator would usually be?

If using the 2 prong flasher is preferred then the idea of diodes would work fine. That is the way the add on 3rd brake light works if you don't want to run a wire all the way up to the brake light or turn switch.

George

It came off of this cab… a 6400. It’s a combo 6 volt regulator and +/- adjustable coil booster of some sorts??? I thought it looked very cool and original, so I cleaned it up and hooked up some oe cloth leads and taped them to the harness. Non functional.

Good to know. Thanks!