Need Electrical Help - Dim H4 Bulb (1 Viewer)

[62LostInMn]

I put SLCFJ62's upgrade harness and H4/H1 housings in my 62 about 6-7 years ago and they have been working great until recently. The driver side H4 is dim now, both for low and high beam. The other three lights work as normal. I also noted that the high beam indicator on the dash is dim. All else on the vehicle is working fine.

I searched the other threads, but nothing jumped out other than to check grounds and change bulbs. A new bulb was no help. The harness ground is good, the ground wire in the harness connector at the bulb is good, the ground to the original harness connector is good. These all beeped out when measured to the battery ground cable.

I measure 12+ volts at the connector to the headlight when switched on. I figure it must be a ground, but I think I've checked all of the obvious ones around the lights.

Electrics aren't my strong suit so looking for input from the sparkys.

Thanks!

 

[OSS]

Reseat the relays for the headlight harness in their sockets. It might just be corrosion on the relay terminals preventing good current flow (maybe).

If the relays are just mounted in the engine compartment unprotected, their contacts will eventually corrode.

 

[Randy88FJ62]

This happened to me as well and it ended up being the socket. Where the wire enters the socket, it was barely together. Seems the way I installed the lights, the harness was pulling or vibrating a certain way to make the wire fail.

Remove corner grill, headlight housing, and inspect socket/wires going into socket.

 

[Skniper]

I put SLCFJ62's upgrade harness and H4/H1 housings in my 62 about 6-7 years ago and they have been working great until recently. The driver side H4 is dim now, both for low and high beam. The other three lights work as normal. I also noted that the high beam indicator on the dash is dim. All else on the vehicle is working fine.

I searched the other threads, but nothing jumped out other than to check grounds and change bulbs. A new bulb was no help. The harness ground is good, the ground wire in the harness connector at the bulb is good, the ground to the original harness connector is good. These all beeped out when measured to the battery ground cable.

I measure 12+ volts at the connector to the headlight when switched on. I figure it must be a ground, but I think I've checked all of the obvious ones around the lights.

Electrics aren't my strong suit so looking for input from the sparkys.

Thanks!

@62LostInMn bit of a dated post, but did you ever resolve the dim driver side H4?? I'm dealing with the exact same issue currently with my 62, swapped bulbs around, swapped the relays around, no change. I also have an upgraded headlight wiring harness.

 

[OSS]

The problem lies with the headlight harness. As I mentioned previously, it's likely a poor electrical contact in either the relay socket or headlight socket if it's not the bulb. Once an aftermarket headlight wiring harness is installed, the original OEM wiring and switches only act as a trigger for the relays to close. It either works or not. No half way

 

[Skniper]

The problem lies with the headlight harness. As I mentioned previously, it's likely a poor electrical contact in either the relay socket or headlight socket if it's not the bulb. Once an aftermarket headlight wiring harness is installed, the original OEM wiring and switches only act as a trigger for the relays to close. It either works or not. No half way

Copy that. So I did just find one of the three female connectors in that H4 socket/plug has broken. One side of the copper contact broke off but is still inside the socket. The crimp on the wire is good and the other half is making contact with the spade on the bulb.

I would think it is making enough contact to fully fire that bulb, I can wiggle that connector around but makes no improvement. Perhaps there is just not enough contact. Just ordered a couple new H4 connectors to splice in to try first. Didn't have time to pull the whole harness to check all connections. Will do that soon.

Just found it interesting that @62LostInMn had an identical issue in the same lamp.

 

[Skniper]

Problem solved, or identified at least.

I contacted the wizard that built this wiring harness and was reminded that each wiring run to the H4’s is fused. The fuses are buried behind my giant battery and I had forgotten they were there. Turns out it was a loose connection in that particular H4’s fuse holder.

For now all lights are functional. I’ll probably replace both fuse holders for good measure, they’ve been in there a long time.