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Hi Bill,
DRL in 700/900s is an old favourite topic of mine. I was starting to prepare an extensive reply on getting your fog lights off the headlamp circuit as there are a number of DRL and foglight systems used in various models, years and markets, and your '93 may be more complicated than most, well more complicated than my '95 anyway. Thinking about why you wanted to do this, I soon realized a likely better and simpler fix was what I did. No wiring changes, simply change the headlight switch to an older style 740 DRL switch. I've done exactly that and it's all I needed to keep me happier than the way it came from the factory.
Our 940s have what's called permanent DRL, leastwise mine and I assume yours based on what you're trying to do. When the headlight switch is in the Off position, the headlights are always on, same as if they were in the On position. In the Park position you only get park lights, leastwise mine, so you do have that DRL option. But the stats prove, and you and I both agree, that something brighter like headlights, driving lights or fog lights are safer in preventing accidents.
What I dislike about permanent DRL and the way Volvo implemented it is that you can never turn all lights off when the ignition switch is in the On position (KP-II). I objected to always having either headlights or park lights on when I was parked and idling, such as getting a little heat inside the car sitting at a ferry terminal on a cold night, as we used to frequently do. When we got our '95 940 weagons (by lucky coincidence both purchased the same day), one of the first things I noticed was permanent DRL that was slightly different and less convenient than my previous '89 740 DRL. I couldn’t turn all the lights off when I was idling, such as when servicing the car. I could see the knobs were identical, so I figured the same switch, different wiring, but when I compared the 740 and 940 wiring diagrams it showed the 740 headlight switch connections were the same, but there was an extra wire off the 940 switch to the headlights. I knew it was likely the switch having an extra terminal. Two 740 DRL switches from the local yard and verifying the terminals visually and with a meter and I was happy again. I wasn't in the mood to butcher the wiring or the 940 switch to do the same thing and I'd want to verify the wiring again bedore recommending someone do it.
I assume your '93 940 has the same DRL headlighting as my '95 940s. I do note the fog light circuitry is quite different. The '95 foglighting is much simpler than what I see in the '94 manual, which will be closer, if not identical to your '93.
In the newer 940 permanent DRL switch, it's internally different with on Off contact that's jumpered to the headlight On contact. That's what's keeping the headlights on in the Off position, there's no magic anywhere else. The earlier 740 DRL switch is identical in all regards other than that internal jumper and associated terminal spade, so has a true Off. I know for sure the '89 740s here in Canada had the older DRL switch that works as I describe. I'm not sure the start/stop years for that older DRL switch in our two countries, but I vaguely recall it was at least '88-'89 here, possibly '87, but not '90 when I believe the regs changed here. DRL was not required on the US, but Volvo of course implemented it anyway using the same DRL as in Canada, but with a switch that gave you an option to disable it. I vaguely recall that a few of the late USA 740s got the earlier Canadian switch without the set screw, but in any case an older-style USA DRL switch can be made to work the same as long as it has the little set screw (behind the knob I believe) and it's set for DRL.
I'll refer you to these old posts of mine for how to identify a suitable old switch.
RWD Defeating 940 DRL Headlights 900 1995
The original post with the details, I'll also post here
RWD day/night lights 900 1995
Best to go on a Volvo dealer parts site and lookup the old DRL headlight switch p/n for an '89 740 (either USA or Canada will do). Expanding the fitments for that switch will tell you other years and models you may be able to use as a parts source. Check the rear lugs as described to verify a used part.
Some final comments regarding your fog light idea. Rear fogs are as bright as brake lights. They are not suitable for DRL use, you need to keep using the taillights. Following traffic may think you've got your foot on the pedal preparing to stop. In Canada (and Europe), we're only allowed a single left rear fog to help prevent that confusion. The right side lamp assembly has a plastic blank instead of the holder. I thought the USA taillight assemblies were the same?
Unfortunately when the taillights are on, so are the front park lights. You're not going to be able to separate the front park lights from the rear taillights
Now as for the using front fogs for DRL, that's an appropriate thought. Front fogs are (I'm crudely guessing) perhaps 1/2 the load of the headlamps on the alt. I took a look at the '94 wiring diagrams, which likely use the same foglight system as your '93 (but different from the '95s). It's not at all going to be trivial, maybe next to impossible, to wire up the front fogs for DRL use, while still having normal rear fog operation. You would need a separate dash switch and separate relay. One of the problems with all DRL systems that don't have permanent headlight DRL is the issue of driving at dusk and forgetting to turn your headlights on. My advice is always against using just park lights for the front as it's way too easy to forget to turn your headlights on at dusk other than people flashing their lights for your attention. Your dash is already illuminated. There are no other cues until it gets dark and there are no streetlights or nearby traffic to light the roadway.
So, in summary, with both of us being DRL believers, my recommendation is that you just downgrade to the older DRL switch so you now have more choice in lighting.
My arguments are as follows:
o Rear fogs are not appropriate for DRL. Where rear DRL is required by the regs, only taillights are permitted. Separating the front and rear fogs and removing them from the headlight circuit is not going to be trivial.
o I've heard the DRL economic savings argument many times before. If you do the research, eliminating DRL entirely is only of minor benefit in extending the life of the alt and minimal benefit in fuel savings, and no contest when it comes to the lifesaving advantages of headlight DRL. In your case of only trying to partially reduce the DRL load on the alt, the benefits would be even less, except of course for the lifesaving part. IMO, it's simply not worth the effort to try getting an extra maybe 6 or so months out of the 9004 headlight bulbs, maybe a month more out of a brush regulator pack and save maybe 1% on fuel doing it the way you planned.
o In my experience, and also given the lack of 940 alternator issues here on the brickboard, the newer 940 80 amp and 100 amp alts themselves last near forever. Both of my high mileage 940s are still on the original alts and surprisingly still on their original regulator packs. That's almost unreal compared to the old 140 and 240 alts I've had. Last time I stuck my finger in to check the slip rings for wear, there was a significant shallow, but not a shouldered groove, so as long as the also worn brushes keep making contact the alt's probably good for another 100+K. A dealer once tried to condemn my 740 16-valve high mount 80 amp alt (different from the other 80 amp alts) a year or two past warranty, but when I took it in for a rebuild they said it was likely a manufacturing flaw they'd seen before with the rear bearings, which they had on hand and soon replaced. All I ever worry about now is over tightening the drive belt and prematurely wearing out the front bearings. I don't even bother keeping spare regulators on my parts shelf anymore, whereas I used to always pack a spare in each car. And if anything ever happens to my alts, I know where to get them rebuilt locally so I'm getting my otherwise well cared for alt back.
Convinced?
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
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