H4 Headlight diagnostics on Centech harness help needed

[bosshoff]

I have a Centech harness installed correctly by my friend John. (Blanking on his screen name, sorry buddy.) I have a H4 harness kit installed. I am not certain if this was originally a function of the Centech harness, as it has been 10 years or so, and I cannot recall. My running lights and dash lights and blinkers all work fine. My headlights are out. It does not matter if I hit high or low. I replaced the headlight switch, and immediately, before I re-mounted the switch up into the dash, the headlights worked. When I put the switch back into the OEM location, they stopped functioning again. I thought WTF? I know there is a circuit breaker built into the switch, I don't think this is the issue. I replaced the H4 relays, to no avail. I do not have any blown fuses. What am I missing? Maybe a ground strap somewhere?

 

[Jdgephar]

The headlight switch only takes in 12V and distributes 12V out to the various places that need 12V. It could be a loose connector in the plug that plugs into the light switch. When you move it, it makes or does not make contact correctly with the mating terminal.

Also check your dimmer switch. Power goes from the light switch to the dimmer switch first, then out to the low or high beams.

 

[bosshoff]

Jdgephar, I spoke to John, (72_EB, btw. ) who also suggested it is likely the floor mounted dimmer switch. I confirmed I have voltage down to the switch.

 

[Chiclassics]

My hunch tells me something to do with the switch. As a first test, try removing it with dash in place and see if it works and then touch to dash and see if it works - if it works before touching dash and doesnt when touching to dash something is pinching inside your switch

 

[bosshoff]

Ok, when I send power to the car (I have a cutoff switch near battery) and headlight switch in "On", the H4 relays start buzzing. I don't let them buzz more than a few seconds, as I am not looking to cook anything. I think maybe the dimmer switch is goofy. It has voltage to it, but maybe it is not passing full voltage along? I've got a new floor dimmer switch inbound. Does this on High Beam and Low beam position.

 

[DirtDonk]

Probably the new one won’t hurt, but why don’t you test the old one right now while you’re waiting?
Take a piece of wire, a pair of pliers, whatever the heck you have laying around, and jumper the center terminal of the connector to either one of the other ones.
With the headlight switch on, that 12 V that you have coming into the switch, should go out to the low beam relay or the high beam relay.
Check both.

 

[904Bronco]

Unplug the switch from the harness, The power wire that you have identified, jumper it to the other two terminals one at a time. If both lights (low/high) work, with the relays activating then you have confirmed the floor switch/or the connections to it are at fault.

 

[904Bronco]

Damn, Paul has quicker key strokes than I

 

[Bruners4]

Poor electrical connections are capable of transferring voltage but not amperage. I've seen this many times. A DMM can be used to measure the voltage drop across an electrical connection. If there is more than 0.2 Volts dropping across the connector, it needs to be looked into.
The reason the relays were buzzing is because of this poor connection. As power was passing to the relay coil, the amperage across the poor connection raised the resistance and the voltage was lowered enough that the relay coil was not able to close the contacts. As the current stopped, the voltage raised enough to then allow the relay coil to close again. This cycling of current through the poor connection caused the relay to 'BUZZ'.