Hi,

I have no low beams on my 1991 740 wagon (non-turbo). When headlight switch is in 3rd position (headlamps) I have no dash/instrument lights, no low -beam, no tail lights.

In this 3rd position I do have turn signals (both the actual lamps and green arrow indicators on instrument/dash panel) - cruise - brake lights - front parking lights and high beams (only when lever is held back constantly, no high beams in "clicked" lever back, lever must be held).

To drive at night I must have the switch set to the 2nd position (parking lights?) - I do have dash/instrument lights in this position but still must have the high beam lever physically held back towards me to engage brights...

I did install a new radio just prior to this happening (I know what you're thinking) BUT I at one time was a car stereo installer in an elite boutique shop in the city. I know what I am doing (yes, I bypassed/disconnected the supplemental amp under the steering column which was necessary as my aftermarket stereo has it's own amp on board and the old Volvo tape deck used that remote amp)...

I triple checked all my wiring and am POSITIVE that I did not steal the ground wire from the headlight circuit nor did I short anything, ALL the fuses are good..

Any ideas?

 

Most likely one of two issues. (1) Headlight electrical ground points are corroded. Check the wiring behind the headlights. (2) Bad headlight relay. It's on the relay panel behind the lighter/ashtray.

 

Thanks BG. It looks like downtown LA in there. Which building is the headlight relay and how would I even go about testing it?

In googling I have also come across the "bulb failure relay" as being a possibility, what do you think?

 

That's odd. The instrument lights don't go through the BFWS. Do your license plate lights work? Sorry I don't have the exact location of the headlight relay.

 

Thanks again BG...

You are RIGHT! I just looked and the plates are dark!!

Is this a good clue?

 

It's a pretty good clue. The license plate lights don't go through the BFWS either. On a 240 the license plate lights come from the headlight switch (2nd position or 3rd position) through fuse 15. No other function for fuse 15. But the 740 could be different. The license plate lights is a pretty simple circuit. Just the bulbs, the fuse, and the headlight switch.

 

Lic plate lights & inst panel lights fuse# 21
Left headlight fuse#17 #19
Right headlight fuse#18 #20


Dan

 

Have you ever figured out exactly what your problem is/was? I am in the same EXACT boat. I've installed radios in at least 5 vehicles with out a problem. i came across the problem before I finished installing the new CD player.

All I have done thus far is taken the lower dash panel out under the steering wheel to access and bypass the external amp (have not touched the actual amp yet). I have also taken the stock radio out cutting ONLY the wires coming from the back of it.

After realizing the headlights would not come on I tried reconnecting the battery wire (green w/ red stripe), ignition wire (orange), and ground wire back to the oem radio. NOTHING.

I then swapped the relay J (electric windows/electric fan) with relay K (central locking/main lighting relay). NOTHING.

I have also checked all fuses..all good.

Anymore insight would be great!

Thank you

 

I also have a low beam headlight issue. They don't come on and all lights go out in the headlight position. I checked my relays and they are fine. It may be the hi/low beam switch. Is the radio circuitry in anyway connected to the low beams? I used this forum post to troubleshoot my relays:

[Inquiry] Driving headlights only work when high beams are selected. Please help. [Response: John Sargent] Are your low beam fuses okay? If they are (and they probably are) you either have a bad high/low switch (unlikely), or a bad Lamp Failure Relay. The Lamp Failure Relay supervises the Low Beams, the Tail Lights, and the Brake Lights, but not the High Beams. Lamp Failure Relays do go bad. Remove the Lamp Failure Relay from it's socket, and test for voltage at the pin connection for terminal 56b, which is one pin clockwise from the pin socket labeled S in the relay base of the Central Electrical Unit. Terminal 56b is the output for low beams from the high/low switch. If you have voltage there, the high/low switch is good on low beams. Re-install the Lamp Failure Relay and test for voltage at the input side the the low beam fuses. If you don't have voltage there, the Lamp Failure Relay is bad. You can pry the cover off and attempt to re-solder it, or get a used one. The headlight relay is energized by the light switch and supplies current to the high/low switch. If it was bad you would only have high beams when pulling the high/low switch towards yourself. In this momentary position, the current for the headlights comes from fuse 2.

 

I know this is an older thread, but I've run into this myself. When I got my 740 it had a cheap aftermarket radio, as I was installing a better system, I noticed that there're two white wires that are intended to the interface with the dimmer, one was not connected. If both are not connected the switch will not function properly, and will play havoc with the lighting system just as described above. An easy fix to a frustrating problem. Thanks for all of the advice above though, my latest issue was the head light relay, and it's resolved now.