Question, would it be possible to retrofit my '88 240 non-cruise car with cruise control? Is the car prewired for it? If not, how hard is it to install?

Have wondered about the same thing on a 740. I seem to remember hearing many years ago that Volvo builds their cars so that dealers can easily add options later on, no idea if that`s an internet legend or true.

does anybody have a good volvo shop manual with a full wiring schematic of a 2, 7 or 9 series car that they can scan and post?

I'll take a look tomorrow and see if I can find any info

I had documents on an old computer with the parts required and the wiring diagrams for retro-fitting cruise control but I have no access to them now, and/or what models it was for etc. I've read that the 90+ cruise control units differ from the earlier type, but I don't know how solid that is.

I'm also interested in retrofitting cruise to my '81 depending on how much is involved (mainly if I could do it myself or not!!). I've seen plenty of pre-'85 240s in PnP with cruise which would be good part donars, if the system worked the same on all engines...

i've got this for a diagram of the electrical of the cruise unit only for a 80-83 240, but the schematic doesnt interconnect the different assemblies.

ok, i found a 1985 wiring diagram,(pg.21) mines a '88 but for spits and goggles i'll check my car in the morning for the appropriate fittings.

1990-93 240 cruise control installation manual from volvo, sorry guys. I guess if i had taken the time to do some research I could have found it. But i will keep looking for more info and keep this thread posted.

http://www.volvoclub.org.uk/faq/CruiseControl.html

Cruise Control Installation Instructions for 740 Cars. [Procedures from John Sargent]

All US 700 series Volvos come pre-wired for installation of cruise control at the dealership. Australian market 700 series, and possibly other market 700 series, do not come pre-wired for cruise control. The following instructions are for US market cars. Volvo used components from Hella on the 700 series cars, as well as 1986 and later 200 series. These instructions assume that you have the components in hand.

The following is a list of the components:
Turn signal control with cruise control function
Vacuum servo, two 10mm head bolts
Vacuum pump and regulator, 3 mounting screws
Control unit
5
Air valve. Automatic transmission cars use one. Manual transmission cars use two
Rubber tubing, and tees.

There are a few model year differences in components.. The brake and clutch switches and their respective sockets for the 1985 and earlier models are slightly different. 1991 and later 740 use a different turn signal assembly to match the dashboard change. All 760 series come with cruise control, however the 760 series uses the different turn signal assembly with the dash change (1988). If you are scrounging parts, the turn signal assembly and brake /clutch switch(es) is the same on 6 cylinder cars and diesels. I have not tried it, but the CPU will probably interchange. The servo uses the same rubber parts on the diesel, but the bracket is different. I don't know if the 16 valve 740 uses the same servo and throttle pulleys.

Turbo and non-turbo use the same servo, throttle assembly, and control unit. The components will interchange between the model years except as noted above.

You will need a Phillips head screwdriver, an 8 mm and a 10 mm ¼" drive socket, a ¼" drive 3 inch extension, a ¼" drive ratchet handle, and a knife. On later cars (1990 on ?) you will need Torx tips to remove the steering column trim.
Remove the trim panel above the driver's feet. It is retained at the top by 2 Phillips head screws along with a plastic plug, and another plastic plug just above the hood release handle. The plastic plug just above the hood release does
Install the control unit. It installs just outboard of the hood release cable and the bundles of factory wiring. You should find a wiring connector with 8 wires, and one with 1 wire. Plug the wires into the unit. The 8 wire connector is polarized and will go on only one way. There are two nail head studs on the outer body panel. The bracket has keyed holes on it for installation on these two studs. The wiring connector end goes down. Optional is the installation of one self drilling screw at the front of the bracket. Both dealer and factory installed cruise controls are often anchored this way. I don't bother.
Install the brake switch, and clutch switch if manual transmission. Remove the metal clip and slide the switch into the hole provided. Install the retaining clip. Check the adjustment of the switch(es) with an electrical meter. I like to just tap the brake pedal and have the cruise control disengage. Plug the wiring harness connector into the switch(es). The connector is white and has a white/black and a blue/red wire. You may have to examine the area closely to find it, as it may be tucked into the other wiring in the area above the brake pedal. If the car has a manual transmission, there will be a connector for each switch. In this case, one connector will have two blue/red wires. The switches are in series, so which connector goes to which switch does not matter.
Route the vacuum hose through the large rubber plug in the left side of the firewall. There are several nipples cast into this plug. Cut the end off of one of these nipples for routing the hose. Some people route the hose through the hole filled by a single rubber plug. Connect the hose to the brake and clutch switches. A tee fitting is provided for cars with two switches. The vacuum portion of these switches will disengage the cruise control in the event the vent solenoid valve in the vacuum pump fails.
Install the vacuum pump. Your 8mm socket will drive the three small hex head sheet metal screws. There are three holes pre-drilled at the top of the reinforcing metal on inside of the left fender well, just under the brake master cylinder. Connect the wiring harness connector to the vacuum pump. This connector is gray, and has three wires in it. Sometimes this wiring harness is well buried with the wiring to the left headlights. If you look, you will find it unless (unlikely) that is has been removed. Connect the vacuum hose you just routed through the firewall to the rear hose nipple on the rear of the vacuum pump. Install the tee fitting near the pump. The tee fitting will connect to the hose from the servo. The front hose nipple is not used. It may be necessary to move the power steering hoses forward from the area where the where the vacuum pump mounts. This is made easier by removing the engine air intake hose, but is not necessary.
Install the turn signal assembly. If your car is air bag equipped, remove the steering wheel trim. Next, remove the old turn signal unit and install the new unit with a right angle screwdriver. If you don't have an air bag, it is easier to pull the steering wheel. Connect the 4 wire gray connector to the short wire harness from the turn signal assembly. Sometimes this connector is well hidden. If you can't find it, it is often incorporated with the harness connected to the turn signal. Sometimes it is easiest to remove the instrument cluster to do this. While the instrument cluster is out, check to see that there is a yellow wire connected to the back of the speedometer. This is the speed pick up for the cruise control. The yellow wire is always connected at the factory, but could become disconnected with instrument cluster replacement, or service light resetting.
Install the servo on the intake manifold. Use your 10mm socket here. It is installed utilizing two tapped holes that are behind and below the throttle pulley assembly. Be careful not to pinch or kink any hoses between the manifold and servo. Connect a vacuum hose between the tee at the vacuum pump, and the servo.
Replace the throttle pulley assembly with the new unit. Use your 10mm socket here. This can be done without removing the snap ring holding the throttle pulley assembly together. Just twist the guide ring to the proper position, and the cable end will drop in. If you have to remove the snap ring be careful not to lose the pieces. Connect all three cables. Adjust the cable slack if required.
Go for a drive. Trouble shoot and adjust as necessary.
Replace the trim panel above the driver's feet. Don't forget to connect the heater hose

a few more

here is another 740 diagram and a link to where some of the diagrams came from. I tried posting the 240 wiring diagrams from that site here, but the page kept resetting before uploading. Very detailed 148 pg document.

http://oak.cats.ohiou.edu/~ridgely/Volvo_docs/

ive got an aftermarket vac operated system that came out of my 244, i dont think i can use it because it wont like boost. for sale maybe? can i use it with a turbo?

do you have any manufacture info on the aftermarket model?

You could probably put it on one of those vacuum only nipples, or actually.. I don't see why it wouldn't like boost?