Headlight relay upgrade issue (1 Viewer)

[tlaporte]

I ordered the headlight relay upgrade @beno posted in the Unobtainium thread last fall.

I’m doing the installation right now, and the way the harness is set up and how my truck’s wiring is, I was trying to go off of the B+ terminal of the alternator, rather than direct off of the battery.

Unfortunately, it’s not working for me. I’ve been chasing it with the multimeter and I have confirmed the following:

• I measure 12V at the B+ terminal
• When I apply 12V to the relays, I hear the “click” to indicate they are good
• When I turn on the headlight switch, I only measure 7V at the female connector
• When all is plugged in, the lights don’t come on when I turn on the switch and I don’t hear a click from the relays

Questions:

• Is that much voltage drop expected? It seems too high to me—but I’m not sure what would cause it.
• Is it likely that 7V applied to the relay is not sufficient to close the contacts?

Potentially useful information:

This is an RHD truck, so I am attaching to the passenger’s side headlamp connector, and the driver’s side connector has a broken wire on the low beam wire.

 

[1969FJ]

Before I respond, can you read and interpret a schematic diagram ?

 

[1969FJ]

I will add an image from a basic wiring and it shows battery voltage constant to relay. Now , the B+ terminal dropping voltage from battery feed is another issue. Can you wire 12 volts directly to relay to test to see if battery is exhibiting the same as B+ ?

 

[S.CarolinaFZJ80]

You are likely getting line loss combined with resistance from the old wiring and switch.
I’d check the headlight switch and clean the contacts. Also use the shortest run from the switch to the lights, i.e. fix your driver side light connector. If that doesn’t work, you may need to run a bypass wire from your battery to your headlight switch in order to get 12v to it.
Maybe some of the more electrically inclined members such as @Coolerman or @RAGINGMATT have some sort of plug and play headlight switch wire bypass?

 

[tlaporte]

I will add an image from a basic wiring and it shows battery voltage constant to relay. Now , the B+ terminal dropping voltage from battery feed is another issue. Can you wire 12 volts directly to relay to test to see if battery is exhibiting the same as B+ ?

View attachment 1931349

When I hooked up 12V and ground (from an ATX power supply) directly to the male connector going to the relays, they clicked.

When I tried to hook it up directly to the battery, with the ground attached to a ground point on the fender, I did not hear the relays click. That might have been due to my jury-rigged setup trying to find a wire long enough to reach.

I think I'm going to do what @S.CarolinaFZJ80 suggests, which is to fix the female harness (@Coolerman has provided me with the parts I need to do that) and see if I can connect on the battery (driver's) side of the vehicle.

I also hadn't thought to clean up the headlight switch and make sure all of the contacts there are good and clean. I perhaps foolishly thought that since the lights had turned on before that everything was good with the switch, but hadn't considered that that might also be a source of power loss and, hence, low light output previously.