Electrical: 240 Right Headlight out

[Malbone]

I've searched the other Headlight posts on the site, but haven't found this particular problem. After successfully repairing my odometer gear, I made the mistake of trying to replace the 9004 headlight bulbs, which I've done many times before. After doing so, the left headlight (hi and low beams) worked well, but the right headlight doesn't work at all. I examined the wiring harness and found that the wires were loose and the terminal grippers had receded into the socket housing. I pushed them back and put in a short extension cable so I could make sure the grippers connected. It still doesn't work. The bulb filaments are intact and using a different bulb makes no difference.

From what I can tell, the relays can't be the source of the problem because they affect both headlights equally. Is that true? Any other ideas? I'm open to replacing the bulb socket if that's the problem, but I really don't want to get into cutting off the socket and soldering wires unless it's really necessary. Thanks for any help you can provide!

[classicswede]

It does sound like the socet on the woring harness. They can suffer with age and heat causing that kind of problem.

[Malbone]

Thanks -- I'll get the socket. Is there a downside to using a crimp connector rather than solder? I'm as bad at soldering as it's possible to be.

[Malbone]

So I started with a fully functioning left headlight (high and low beams) on my 240, and a dead right headlight. Both 9004 bulbs were good, since both worked fine in the left headlight. I suspected the right socket was bad because the wires were loose and not gripping the bulb plugs. Wiring tested good with a VM.

I bought a replacement socket and some crimp (butt) connectors, clipped off the right wires and installed the 3 replacement wires as carefully as i could -- I am terrible at soldering and not much better with crimp connectors.

The result was that the replacement socket worked, but only the high beam. I thought I had done a bad job with the connectors, so I removed them and tried again -- same result, only the high beam worked. But now the low beam on the left is also not working!

That sounds to me like a relay issue, but the relay at least make a reassuring click every time the beams are switched. I may have jostled some of the relay connectors in disconnecting the battery.

What do people think? Time for a new relay, or take the old one down and try sanding the connections first? The existing relay is either OEM or a replacement from no later than 2000.

[JRL]

Relays out and make sure they aren't showing any signs of being burnt or dampness in the connection. Maybe a spray of switch cleaner (Maplins) might help.

[Malbone]

Found the main headlight relay (under the carpet near where the driver's left foot would be while driving -- wouldn't have been my first choice for where to mount electrical connectors). Couldn't get the socket connector off, but there is a gap between it and the relay that allowed for test leads to be inserted; relay seems to be putting out 12V. No evidence of melting or burning, and what I could see of the contacts was shiny and uncorroded.

I took a look at the hi-lo relay. It is very close to the battery and power steering reservoir, so removal (without losing the screws) will be tricky. I took off one screw and rotated it a bit; no obvious damage, but the connectors are on tight and I don't want to remove them without having a replacement ready.

While I was jiggling the relay (and working on the street) the alarm in the car ahead of mine went off for no apparent reason. I thought it might be my fault (or the relay's fault), but the battery was disconnected at the time. Nothing in my '90 240 could have been transmitting radio signals, right?

[Malbone]

So when I had no low beam in both bulbs, I bought a new hi-lo relay and put it in. I inspected both bulbs and found that one bulb had a bent low beam prong, so of course that bulb won't have a low beam. I put in a new bulb and have both beams on that bulb.

That leaves the other bulb, which still doesn't have a low beam. I had previously replaced the bulb socket, and thought perhaps I had wired the connection incorrectly, but both sockets tested identically with a voltmeter -- 12 volts on the low beam (center prong), then 12 volts on the high beam when switched to high.

Both bulbs are new. I can't understand how I can have power to the socket but the low beam still fails when the bulb is put in. Any ideas? Help!

[Malbone]

Still have only high beam on one side -- the side where I replaced the failed socket. I made sure the new socket was wired correctly. Both right and left test identically with a voltmeter, but I'm a bit confused: When switched to low beam, I get a 12-volt reading when connecting the low beam hot to ground, but I also get 12 volts when connecting the low beam to high beam. When switched to high beam, I get 12 volts only when connecting hot to ground.

Again, I get these readings on both headlight sockets, but the left headlight works fine and the right headlight only works on high beam.

Does this mean there is a short somewhere in the wiring harness? Should I just replace the whole harness (assuming I can find one)? Or is there a less invasive repair that might work?

[CaptainAhab]

If you have power at the connector then the problem is downstream.

Connect the volt meter across the low beam and ground on the connector, if you are seeing 12v then circuit is OK, if not then you have a bad ground. I don't think it will be the ground as it's common to both beams, but best to check.

Next is making sure the bulb is good, compare the resistance of the good low beam element to the problem one. If you have a very high reading or open circuit then that's your problem regardless of what the bulb looks like.

If the element is good then the only thing left is the connections between the circuit and the bulb. Check the resistance of the connection between the cable and the spade connector. If you have a high resistance here and a load (your bulb element) is applied, the current flow will be drop and the element won't glow.

A common problem with old auto wiring looms is that the insulation can break down and become slightly porous, leading to ingress of moisture and corrosion of the copper. This makes the copper look dull or black and means the surface won't conduct (or solder), so your crimp connections won't conduct.

If this is the case, get some bicarbonate of soda (baking soda) and mix it with water. Dip the ends of your stripped wire in this for a minute and it will clean off the corrosion, then dip them in vinegar to neutralise the alkaline and prevent more corrosion. You should now have lovely bright shiny copper.

If you want to see how effective this is drop a blackened 2p coin into this mix for a minute and see the results.

[Malbone]

Thanks for the suggestions -- however, the cold weather forced me to stop repairing the car on the street. I took it to a good mechanic, who determined that it was the bulb failure sensor that was bad. Replacing it brought the headlights back. I hadn't suspected it, because the sensor hadn't been working right for some time, lighting up the warning light when all bulbs were good. I suspect it developed an additional fault that caused the headlights to go.