'97 850 Driver Headlight has me stumped

[djm850]

erikv11, I really appreciate that offer, but I have already purchased one used off of ebay this morning. I'm hoping to pop it in and have success, but now I'm not too hopefull. I am completely lost when it comes to diagnosing electrical and do not know how to use a volt meter. Could someone explain exactly how to check in baby steps? I'm assuming I would be checking both headlight bulb housings with the lights in both low & high beam setting and looking for less than 12v or none?

[erikv11]

Yes, that is essentially what you would be checking. It would be interesting to know what voltage is being delivered for each of those combinations. If you can install a headlight you can use a voltmeter, you just need some instructions.

These both look pretty good but I didn't go through them all the way:
https://learn.sparkfun.com/tutorials/ho ... multimeter


I would measure the voltage from each headlight connector terminal to ground (e.g. to the car frame). The ground wire for the lights will never show any voltage, you will soon know which one it is.

[cn90]

- Not a relay issue: if bad relay BOTH sides will be affected.
- You have new HL assembly: so unlikely to be bad wiring INSIDE of the HL assembly

Since your problem is limited to the LEFT side, I suspect the wiring (from the relay to the HL assembly) is bad.

Check the connector itself carefully. Look at the crimps where the wire is crimped into the connector.

Go to youtube and learn how to use a Voltmeter. Very very easy.
Black probe is ground. Red is +.
Turn the key to position II during testing. You should get 12V to the connector, just before it meets the HL assembly socket.

Below is a good thread:
http://volvoforums.com/forum/volvo-850- ... air-17050/

[djm850]

It appears there may be a ground issue with the driver side headlight. We only tested the harness end of the connector(s) and tested two ways. First using both the probes on the connector with the red always in the middle contact (power) and probed the other 2 contacts with the black probe. We got give or take 11.8v at both lights. We then we put the black probe on the (-) NEG post on the battery and then probed the 3 connectors with the red. Here's where it got interesting. The known good headlight side (passenger) got 11.8 volts but the drivers side didn't. How does the headlight assembly ground itself?

[jblackburn]

There are chassis ground points more or less behind each headlight - thick blue wires. I should think they would ground out there - Check their contact points.

[cn90]

See photo:

- RED Circle: HL Assembly is new...leave it alone

- BLUE Circle: check the wiring for ground issue: Use "OHMmeter" feature on your digital multimeter and probe the black wire and good ground. It should be zero Ohms.

Easier solution is to bring in fresh ground to the black wire. One end goes to known good ground on chassis and use a splice connector or butt connector to connect to the black wire.

This should solve your problem.

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