1996 Volvo 850 tries to start when I connect the battery cables

[tryingbe]

The big red cable from the alternator to the starter to the battery is HOT all the time. Your issue is NOT there.

I really don't want to nag, but this is my third time saying it. Follow the wiring diagram I provided and check the circuit.

[Myvolvo850]

There is power to the green/red wire to the ignition switch even when there is no key.. I unplugged the power circuit plug. And still have power to the green/red wire. Not even quite sure what that plug is for.. where do I find that transmission range sensor?

[BEJinFbk]

Should the red battery cable show power to the starter at all times?

It's connected directly to the battery, so yes.

If the starter doesn't keep running when the small green/red wire
is disconnected, it pretty much has to be a bad ignition switch.

The only other contacts in the run from the ignition switch
to the starter are the PNP and the alarm's starter cut relay.

And the PNP contacts and starter cut relay interrupt the
starter trigger circuit, so they aren't likely suspects.
The ignition switch contacts are the only only set that
connect 12 volts to the starter through that circuit.

Refer to the diagram and start shopping starter switch
contact blocks. Most folks suggest sticking with OEM.

[Myvolvo850]

I replaced the ignition switch and it continues to try and start still so is the pnp a possible problem? I'm great with mechanics but this Volvo is a different animal I just bought it about 2 months ago... I've never seen a vehicle do this lol

[tryingbe]

What is a "power circuit plug"?

Did you try to remove the alarm relay to test?

[MadeInJapan]

It is amazing that this came up here. I don't recall if I posted this exact thing with my S70 2 or 3 years ago or not...I had a kill switch for my starter because it did this exact same thing. I also replaced the ignition switch as well as installed a new starter- nothing changed. Then one day I was fooling around under the starter and found a bare wire. I'm still not sure which one it was, but I taped it up and my problems ended. Look for a wire that is shorting giving your starter juice even when the key is out.

[MadeInJapan]

Read this thread all the way through! Here is how crazy my car was...no problems however since I found the wire and covered it.
https://www.matthewsvolvosite.com/forums ... =1&t=51006

[BEJinFbk]

A little more good stuff on this topic:

2/28 is the alarm system stuffed into a dual relay sized package.
It includes the alarm brains and the normally closed starter cut relay.
( It also handles locks, interior lights and door open alarms, IIRC ).
This relay opens the starter circuit when the alarm goes off,
otherwise it passes power right through to the starter.

3/71 is the PNP ( Transmission Range Switch ).
It only allows power to pass along to the starter when
the trans is in P or N, so the car won't start in gear.

17/1 is the underhood starter service connector.
It lets you inject 12 volts from the engine bay so
that you can bump the starter over during service.
It should be disconnected and hanging free.

[abscate]

Pull terminal 50 off the starter and the starter trouble will end. If it doesn't, replace starter.

If you have to drive car, put a new wire on that terminal and run it up near battery, and tough to the positive terminal to start. Car in park when you do this as you are bypassing the PnP switch.

Now you need to find where 12 VDc is getting onto your disconnected terminal 50 wire. It will be a failure of insulation in the harness somewhere, if you have ruled out the ignition switch.

[Ozark Lee]

I don't think that you have indicated but do you have any aftermarket equipment installed in the car? A bum aftermarket alarm/remote start setup might cause your problem and it will be difficult to sort out. I just wound up yanking one completely out of my son's 850 after it wouldn't start.

One other thing to do is remove the 210/211 relay and see what happens. That will tell you which side of the firewall to focus on. With the relay removed it should not crank with the key and it certainly shouldn't try to start without the key. If it still tries to start with the relay removed then work your way forward through the harness under the hood.

...Lee