petrolhead

Does anyone understand the headlight isolation relay circuit? When I turn the headlights on, the relay activates, but there is a white wire that I believe is the constant supply voltage, goes dead, so the pink wire gets no voltage. Here's a diagram. Also what's the purpose of the isolation relay? Whey is a relay powering up 2 other relays? What if it was bypassed?

deadbird

Red / Green - Power routing when headlamps are on

Pink / Blue - Power routing when lamps are off.

The yellow wire has +12v when only the headlamps are on (makes lights go up).
The isolation relay helps to reverse the power to the motors.

The white wire has +12v when head and park lamps are turned off (makes lights go down)

petrolhead

I'm understanding the whole thing now. I have a bad isolation relay. the pink wire is not getting power. I was scratching my head trying to figure out where the load to power the pink wire could come from. then I realized that the pink wire is only powering another relay, so the yellow wire from the switch will do just fine. I took an easy diagnostic and made it hard for myself on this one. Now to find the super rare isolation relay...

brettr81

the isolation relay protects the motors from voltage spikes, which if you've replaced your relays they will anyways. Its my understanding that it is not made anymore and a pita to find. I had one go out in a Fiero and I ended up just bypassing it. You can also build your own.

petrolhead

Well, like everyone says, I can't find a relay anywhere. Has anyone done the dual relay conversion? I see it's been done, but no real info on it.

LX_SS

Plenty of aftermarket dpdt relays out there that do the exact same thing as the original using 1 relay.

brettr81

Check Fiero forums. I believe pennocks has a lot of stuff on it.

petrolhead

Does anyone have a part number or application that it fits?

LX_SS

Multiple companies make them, They are a double pole, double throw relay.
I'm not from the US so i wouldn't know where to get them but i do know they arn't a rare part, The original pontiac one might be tho.

http://www.jaycar.com.au/Electromech...Relay/p/SY4065

Is just an example of one.

Of course as any aftermarket goes, you will have to re-wire the connector to suit.
But you can use 3 of those relays to replace all of the original relays if needed.

brettr81

http://www.fiero.nl/forum/Forum2/HTML/120467.html

There are lots of threads about the isolation relay, either rebuilding, making a replacement, or just wiring it to bypass and putting in a toggle switch to keep your headlights up (so they don't go down everytime you shut off your headlights). Fieros used the isolation relay every year they were made besides 88.

petrolhead

well after searching all over for a diagram to replace the isolation relay with 2 regular 5 pin relays with no luck, I figured it out myself, and made a very poor diagram to share.
Here's a quick circuit description.
Up relay,
circuit 30 goes to the yellow wire, which is powered up when the switch is turned on.
Circuit 86 is the power supply to the relay, I tied this into the yellow circuit 30 wire. This would normally be a high amp circuit, but since all I'm doing is powering another relay, and it's only going to run for about a second, I don't see a problem, otherwise you will need to find another power source.

Circuit 87 is the supply voltage from your new relay to the headlight relay. It goes to the pink wire in the isolation relay connector.

Circuit 85 is ground, tie both relay circuits together and attach them to the black wire.

Down relay
There are 2 blue wires, one has a white stripe. These are your circuit 87 wires, tie them together.
I actually reversed circuits 30 and 86 to how the relay is supposed to be wired on this one, because when you turn the headlights off, the white wire is energized by the headlight switch to close the headlights. The relay will stay on while the car is off, draining the battery. Again There is no amperage to speak of, so I don't see a problem. The only disadvantage is that when the key is off, the headlights will not close, but they will open.

So Circuit 30 goes to the white wire, and 86 goes a keyed ign. source, I ran a wire to the fuse box.

My headlights go up and down perfectly, hope someone can use this.

T/A-MAN

Had the same trouble with my isolation relay. I wasn't able to find a new one or even a good used one, but I was able to fix my isolation relay by using a coil from a new relay and installing in my bad isolation relay. Worked perfect and I have headlights again. Also was able to pick up another isolation relay that was bad and did the same to it for a backup. Let me know if I can help you.