I posted last week that I was planning on replacing the wiring harness in my 740 Turbo. Weather prevented it last Saturday, but I'm going to try again tomorrow.

I have been wondering if I need to use something like dielectric grease on the connectors.

Also, regarding replacing vacuum lines, this may be a stupid question, but is there a reference anywhere that indicates where the vacuum lines are in a 1986 740 turbo?

Thanks, and wish me luck.

Joe

I just changed mine a couple of weeks ago so it is still pretty fresh in my mind. Although some folks have changed it without pulling the manifold out, I found that I could see what I was doing a lot easier with it off than with it on. The turbo models do have a lot of hoses running along side the injector wires so it is pretty tight in that area with the manifold on. I had mentioned this in a previous post, but it is worth mentioning again. I highly recommend a 13mm swivel socket for pulling the manifold nuts off. You can easily remove all of them with a swivel socket. You would need to replace the gasket if you pull it off. The new Volvo gaskets are thick and soft so they work well.

Most of the vacuum hoses can be changed easily at any time so you don't necessarily need to do them during the same job.

I also very much agree with one of the other posts about being aware that not all connectors and cables will be replaced - don't damage anything unless you are sure it is on the new harness. You don't neccessarily need to label everything before you start, but it is a good idea to look at the harness and identify each connector before you start. The installation document you should have gotten from Dave is a good reference to check when you think you are done.

My only mistake was that there are two lugs on my starter and I connected to the wrong lug. There was no damage done, it just would not activate the starter. It was easy enough to figure out.

The only connectors that are hard to reach are the ones under the manifold and the oil pressure sensor. That one has to be routed from the bottom of the car near the harmonic balancer.

There is one really big connector near the ignition coil. It was very difficult to unplug so I cut the harness and pulled out 1 pin at a time. There are some unusual retaining clips on it so watch out for that. The connectors easily poped apart after that. Again, be absolutely sure you don't damage something that stays in the car. I found that cutting the old harness makes it easier to get out, but you can not make any mistakes. I used a razor saw to cut it in one or two places.

Mine took me about 6 hours. I was also replacing my injectors due to a gas leak so I removed and cleaned the manifold at the same time. It is a lot of work, but not that hard to figure out.

Good Luck,
R Duke

Important, to resolve any problems you might have, as your removing the old harness install the new harness, just have it right behind the old one, as you unplus something plug the new one right back in, this will deff save you time of going hummmm am i going the right direction with this guy etc etc, thats what i did on my 86 740t only took me 30 min to change it out being carefull.

Use dielectric grease on ALL connections EXCEPT the oxygen sensor.

The vacuum lines should all be there: just replace with similar inner diameter hose or tubing. Your car has a schematic diagram under the hood, probably near a strut tower.

On the harness...be careful what you rip out and replace....I had the engine harness replaced on my 87 and not all of it comes with a 'harness'. They got all the deteriorated wires, but there were other OEM wires that weren't replaced. Best thing to do is look carefully at your new harness and disconnect/remove ONLY identical parts on your engine harness.

On the vacuum lines...when the car left the factory there was a vacuum hose diagram somewhere under the hood, probably on the passenger side engine firewall. If it's been scraped off or is illegible, you can probably look in a service manual (volvo for sure, maybe bentley) and get the general idea.