After installing the dash and all the various switches in my '68 122, I still have one black wire, and can't seem to figure out what its for. I can't find it on the wiring diagram in the Haynes manual. I tagged all the other wires when I removed them but must have overlooked this one. It runs through a black plastic tube or sleeve along with a red & a gray wire which go to the dimmer switch on the floor. From the dimmer switch onward it must be 3 feet long. The other end goes through the firewall near the fuse block and is about a foot long. Since it goes through a sleeve I'm assuming it is factory original equipment. Has anyone run into this before, or have a clue where it goes?

The dimmer switch has three wires going to it. One is hot whenever the headlight switch is on, one goes to high beam and one goes to low beam. Seems to me you have just what you need for the dimmer switch. Tom

Did you / do you have OD. I think the wire to the OD light on the dash is black and runs to the OD relay. The light from the OD switch is also black and runs to the OD relay.

Perhaps the wiring loom on the later cars includes the OD wire even if its not equipped with OD.

1st clue, 1968.

The black wire inside goes to the parking brake warning switch and the black wire under the hood is connected to the brake pressure warning switch on the splitter from the brake master cylinder.

If you ground either wire, the red warning light on the left corner of the dash will illuminate with the key on if you still have the light and if it has a good bulb.

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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com

Planetman wins again!

Here is a link to a nice coloured wiring diagram.

http://forums.swedespeed.com/showthread.php?220033-Wiring-Gremlins

It's way down the page. It does not have the e brake circuit included, and I have yet to notice if there is a wiring diagram wth the e brake circuit included, in my case I found the wire and worked it out, my 65 and 67 did not have an e brake circuit.

As usual, Planetman, you were exactly right on the mysterious black wire going to the switch for the parking brake. I found the remnants of the old, badly corroded switch, and discovered that it is identical to the door contacts. My old 544 parts car uses the same part so I will be installing it ASAP.
Many thanks to everyone for all your help.

How about the black wire under the hood?

Do you still have dual circuit brakes? If you do, the black wire is supposed to be connected to the brake pressure warning switch located on the 1st brass splitter.

It was not uncommon to convert back to a single circuit master when the dual circuit masters went NLA.

FYI, there are new reproduction dual circuit brake masters now being made.
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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com

The black wire is still under the hood, but I guess a previous owner converted back to single circuit brakes. I read somewhere that an aftermarket Wilwood master cylinder will bolt right in, and are available in several bore/piston sizes. Any thoughts about doing this? Thanks

Because I am in business and I have to worry about liability issues, I won't use a Wilwood brake master on any street legal car.

I recently restored a dual circuit 122 back to a dual circuit brake master after being sold with a single circuit brake master cylinder. I used a new reproduction cast iron dual circuit brake master and made new brake lines. Because the brass splitter was nowhere to be found, I installed a brake fluid reservoir cap with a low level float switch from a BMW and wired it to replace the stock brake pressure warning switch.

I do sell Wilwood clutch master cylinders to use in 122 and 1800 Volvos and I know the bolt pattern for the clutch master is the same as the Volvo brake master for the 122 and 1800 so it might be possible.
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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502

I figure if a Wilwood can stop a race car going 120 mph, it'll stop a 122 going 40.