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Old 10-20-2016, 07:17 PM   #1 (permalink)
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MPGeo - '93 Geo Metro Base
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Exclamation GEO LED Headlights Wiring Conversion

If you own a GEO, and thinking about doing an L.E.D. headlight conversion...

L.E.D. 4x6's are NOT Plug-N-Play for these GEO cars.


So I recently purchased a pair of LED 4x6 headlights and had to find few things the hard way... and I want to share them with you.

Yes the harness needs to be modified, but that's not the problem.

As it turns out L.E.D.s are polarity specific. Meaning, that your ground and battery supplies HAVE TO be on the correct location. Reversing the wiring will simply not allow the light to come on...

In turn old-style incandescent bulbs don't care how they are wired, as long as they have a ground and a battery supply, they will come on.

Simple enough... Until you start wiring your new harness in and find out things are not working quite right

As it turns out, the headlight wiring harness on this car uses a dedicated battery supply that is constant, and the headlight switch internal relays provide the ground to either the Lo/Hi sides to complete the circuit. Since the incandescent bulbs are not polarity specific this works great.

Most other manufacturers would have used a constant ground, and have supplied the battery supply for either Lo/Hi to complete the circuit. Since the L.E.D. headlamps are universal, they assume your vehicle is wired this way. I guess this was supposed to be the wiring norm of the day?

Therein lies the problem:
Metro = 2 switchable Grounds & 1 Positive constant supply
LED = 1 Ground constant & 2 switchable Positive supply

What this means is that you can only have either Low Beams or High Beams, but not both! Since I had to go to work early the next morning I opted for Low Beams

So the next morning during my work break I was brainstorming how to make this circuit work for both Lo/Hi beams and the obvious solution was to add some extra realys... but I did not want to run a bunch of new wiring so I wanted the relays to be close by the headlights. This meant I might have to buy four relays, 2 per headlight (1Hi/1Lo)... that's over $40 in relays, I only paid $55 for the lights... So I figured a way to make the circuit work with only one relay per side.

This is a "cleaned-up" version of the schematics

So I built the circuit and tested it on this here prototype & it worked...

It's actually not that hard, once you figure it all out, and this is what mine looks like

The constant power supply from the OEM harness will be connected to (3) three locations (where the yellow cable is) This supplies the power to the relay terminal #30, and also supplies power to either realy terminal #85 or #86 (to energize relay). The OEM power supply also has to provide power to the Low Beam positive head lamp terminal.

The OEM ground supplied for the LO beam still goes connected to Ground on the LED harness.

The OEM ground supplied for the Hi Beam goes connected to the other terminal... either realy terminal #85 or #86 (to energize relay) (which ever was not used by the OEM power supply)

A diode has to be bridged between the LO ground & Hi Ground as shown... This is the key to the whole thing. I used a 3 amp diode on mine. If you install the diode the wrong way then you will simply have Hi beams for both Lo or Hi settings. When you have it the correct way your Lo ground will not energize the relay, and the Hi ground will energize the relay.

The Hi Beam on the Head Lamp connector has to be connected to the Relay terminal #87 so that when your Hi beam ground energizes your relay it then closes the circuit for the Hi-beams and supplies it with a battery supply rather than a ground.

This is how it looks on my car

So far it is working great, and as expected, I'll see how long the 3amp diode holds on, I might upgrade to a 5amp diode and that will be plenty!

I purchased the wire terminals strip section from Lowes Home Improvement, it was a 12 terminal strip and I cut it into 3 four terminal segments and using only one 4 terminal segment per side as pictured.


Low Beams Shown Here

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