Turn Signal indicators, 2 instead of 1 Options

[John]

Has anyone rewired a later model car to that of an early model car to get individual turn signal indiators?

The early style was wired so that each indicator light (in the tach) had one of the turn signal wires (black/white stripe or black/green stripe) and the blue/white stripe.

As far as I can tell, the flasher relay is the same, but the wiring is different due to the fact that the 1974 and later cars only had the single indicator light in the tach. The 74 wiring diagram shows the indicator light wired to the blue/white stripe and ground.

Is this rihgt or not.

maybe I'll wire it up and find out.....

[jk76.914]

All right. Back again. Here's the schematic for the '70 - '73.5. These are the cars with separate left and right indicators at the top of the tach, and the high beam indicator along on the bottom...


Thankfully, the flasher works the same as in the later models that only have one indicator, which was covered in my earlier post.

When you look the indicators, it gets weird- The same blue/white wire goes to the tach, and it hooks to BOTH bulbs. The other lead of each bulb, instead of going to ground, actually goes to the turn signal circult that goes off to the bulbs themselves. BUT WAIT!!! The LEFT indicator is connected to the RIGHT circuit, and the RIGHT indicator is connected to the LEFT circuit. (IMG:style_emoticons/default/WTF.gif)

If you study what's going on, you see it. When the left turn signal is on, the flashing signal trailing out to the bulbs is +12v/0/+12v/0/+12v/0 and on and on. The same signal is coming out from the secondary relay to both indicator lights. This signal is in phase with the primary flashing signal, so the indicator that is connected to the left turn signal WILL NOT FLASH because it will see +12v on both leads at the same time, or 0 on both leads at the same time. There will never be a voltage differential that will cause it to light up. And which indicator do you NOT want to see flash when the left signal is on? That's right- the RIGHT one.

So what happens with the left indicator? It flashes! Because one lead is connected to the same secondary flashing output that the other indicator is connected to, but its second lead, which is connected to the RIGHT signal circuit IS GROUNDED THROUGH THE TURN SIGNAL BULB FILAMENTS THEMSELVES! (let sink in)

This grounding scheme works because the indicator bulb is much lower wattage (meaning much higher resistance) than the main signal bulbs, so it lights up and limits the current in the circuit to a level below which the main bulbs turn on.

So that's pretty tricky, but it's not over yet! What happens when a bulb is out? Well, the secondary relay in the flasher stays open, as before. But what a weird-ass result that has- BOTH INDICATORS FLASH TOGETHER when the side with the missing/wrong/corroded/LED/whatever problem is turned on. (IMG:style_emoticons/default/WTF.gif)

If you look at the circuit, you can see what's going on- with the output from the secondary relay floating, you have both indicator bulbs, in series, completing the circuit from the side that's on (+12v or thereabouts) to the side that's off, and grounding through the filaments of the big signal bulbs again! The indicators are a bit dimmer, because they're wired in series, but they flash together.

If you replaced your indicators with LEDs, this cannot happen. The back-to-back series LEDs will block current flow. In this case the indicator that a bulb is out is that the indicator LED on the side with the bad bulb will remain off when that side's turn signal is turned on.

So that's about it. These two installments show the before and after circuits for incorporating early dual indicators into late tachs... Plus enough info to dispel myths that are drifting around about grounding problems, diodes in the harness, etc, etc, etc.....

You can now also figure out how to diagnose problems better. For example, if the dash indicator light is on, but doesn't flash, it has to be a bad flasher. If the signals flash, but the indicator is steady, it's the secondary relay in the flasher. If both stay on, it's the primary relay in the flasher (probably) or the solid state timing circuit in the flasher (unlikely). etc, etc, etc....