H4 Headlight upgrade wiring question (1 Viewer)

Joined
Dec 31, 2009
Messages
571
Location
Tucson
 
 
Ok, so I am going to upgrade my wiring harness so I can run my higher output H4 bulbs. I have a couple of the popular wiring diagrams off of this site for this and now I have reached a stumbling point. From what I can find online and searching, the poles on the back of an H4 bulb are as follows.

low


com Hi

Also from searching I found that the fj60 harness sends 12v positive through the switch to the com. pole. And that the negative pole is the one that is switched when you go from low to high beam.

I wanted to test my harnesses output at my plug so I unplugged my headlight and did some testing on my plug on the drivers side. I don't have my multimeter with me but I do have a test probe with a lamp. I am getting some strange outputs from my plug and want to know if this seems strange to anyone else.

When I tested my plug I placed the alligator clip on ground and inserted the probe into the plug and got the following results.

High beam setting -- All three poles lit up my light!

Low beam setting -- The two vertical poles light but not the horizontal pole.

This really has me confused because the way I understood it one pole ( the common pole ) should be 12v all the time when the headlight switch is on. The other two should be grounds only when switched on, high or low respectively.

I thought this would be a simple test to tell me what my outputs are at my plug before I start wiring up my harness and relays, but now I really don't know what is going on.

If anyone knows what the outputs at the plug should be for the headlights on a 9/85 fj60, I would sure appreciate the help on this.

Thanks,

Don
 
Joined
Dec 31, 2009
Messages
571
Location
Tucson
 
 
Somebody must have built their own harness and checked out their system before?

Anyone?

Thanks,

Don
 
Joined
Dec 31, 2009
Messages
571
Location
Tucson
 
 
Thank you so much for that post! It really helped. I got my harness finished up today and it workes perfect. Man I should have upgraded these years ago, now I can finally see at night.

Thank you again,

Don
 
Joined
Mar 6, 2008
Messages
329
Location
Sierra Madre, CA
 
 
Thank you so much for that post! It really helped. I got my harness finished up today and it workes perfect. Man I should have upgraded these years ago, now I can finally see at night.
What lights are you using and where did you buy them? It's on my to do list also.
 

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