Headlamp plug wire ID help

[Galaxie64]

I am wiring the aftermarket 12V harness and headlight system from LMC into my '51 and the harness that comes with it just has the standard 3 prong plug to plug into my "stock plug" There is no stock plug on a '51 so I need to know what the 3 wires are on this plug, it is the standard 2 on top 1 on the bottom in between them. It probably means nothing compared to stock colors but looking at the back of the plug the low middle wire is white the upper right wire is brown and the left wire is blue with a white tracer. If nothing else if I knew the layout of the relay I think I would be set, are they all universal? I ask on this board because I am 99% sure this harness is plug and play with the bumps.

[390Nut]

Universal relays are pretty standardized, and if you look at the wires on the relay harness, and then pull a relay you should be able to figure it out, as the relay posts should be numbered on the bottom.

Generally speaking, #87 and #30 are your power wires. They can be reversed at times, meaning power-in from the battery goes to #87 or #30, and power-out (to the lights) is the opposite post.

Same with the #85 and #86 posts, one is the ground, and one is the trigger from the original harness.

Some relays have a #87a post in the center, so that when you turn your lights OFF, (or whatever you are powering) that post turns on.

As you are looking at the back of the standard sealed beam (or H4 bulb) the left terminal is the ground, the top terminal is the high beam, and the right terminal is the low beam.

[Galaxie64]

Thanks, all that should get me going. I was trying to figure it out just by what wires went where in and out of the relay harness but started confusing myself the more I thought about it.

[390Nut]

I was trying to figure it out just by what wires went where in and out of the relay harness but started confusing myself the more I thought about it.

Been there done that, was given the t-shirt too many times.

If it doesn't work a certain way, you could try reversing the wires. For example, try reversing the #30 and #87 wires, as sometimes the relays only work one way; can't remember the specific details, but some relays are "Normally Open" and some are "Normally Closed".

All depends on the relays you have.

[kid]

A normal open and a normal closed relay would not care is you switched the relay control wires. Some relay coils can be DC or AC and for the coil to use AC they put a diode (one way electrical gate) in the coil of the relay. If the DC is routed the wrong way the diode will also hold it from going through and this will stop the relay from working.

A headlight relay should be a single pole dual throw relay meaning that it makes contact whether energized or not. The high beam switch comes on and send a coil to the other position turning on the high beam. When the low beam gets turned on the switch is not in high beam and the relay falls to the opposite side.

The light switch turns on the light power relay. It also powers the foot switch which switches the light high/low relay. When the light switch turns on, the light relay turns on power to the low beam contact of the high/low relay. When the foot switch is switched to high the high/low relay switches to high and you have high beams.