pin assignments for head light bulbs

[Nick68]

Does any body know what the pin assignments are on the back of a 7 inch mustang bulb? There are 3 pins on the back - however they are unlabeled. I am wiring the car from scratch so there is no original wiring harness or colour coding to go by.

Can anybody advise which pin is which?

[hybrid]

It should be the same as H4's etc.
Give this a try:

[hybrid]

To make sure, you can use a multimeter to test the pins.

- To find the low and high beam pins, find the two pins that have no continuity between them. The other one is ground (-).
- High beam are generally higher wattage, so will have a lower resistance between it's pin and ground.
- Low beam is lower wattage and will have a higher resistance between it and ground

[Nick68]

Perfect thanks hybrid - the H4 diagram above is consistent with my attempt at reverse engineering.

Many Thanks

[hybrid]

Just for the record (in case someone wants to know this later. After thinking about this, my comments on the tests to perform were wrong anyway.
Because of the common earth, the high and low beams WILL have continuity between them, but they will have the highest reading across them, because it will be measuring across both filaments in series, which will add both resistances together.

[Nuts]

Here you go Hybrid, this should help

[nassi]

Thanks Nuts, finally after 41 years of applying Ohms law I now understand it. :rotfl:

That really is the best visualisation/explanation I have ever seen.