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940 Starter Relay Install - 1993 940 turbo


It Never Ends
Dec 10, 2015
Toronto, Ontario, Canada
My starter has been giving me all sorts of issues latey. 90% of the time I'm finding myself shorting the starter solenoid with a screwdriver to get it to work. I have seen on here a couple times that installing a starter relay in line could be a solution to this.

Does anyone have any diagrams and/or images of where it might be that I would have to install this starter relay?
What is the point of this starter relay? Volvo themselves did not fit one to any classic Volvo that I know of

The starter electrical circuit for the 2/7/9 series tends to be problematic. Notorious for current drop between the ignition switch and starter solenoid. The real problem is heat soak at the solenoid. If you set up a relay instead that is hooked to the starter trigger wire and has full battery voltage coming to the switched connection it eliminates the issue. I did this for a customer with a 1993 240 that had starter problems almost every time it got hot out. Once she would park her car for more than 5 minutes the solenoid would heat soak and the engine would not turn over. It's an old trick that comes from GM starters that are designed exactly like the Volvo starter doing the exact same thing. I had to do the same "fix" to my Chevrolet 327 powered 242. On a hot day you would have to open the hood and let the starter cool off before it would restart. The relay trick cured that car's problem as well.
I didn't read through ^^^ that thread, but you want to change the starter wire so that it energizes a relay and that relay then supplies +12v to the starter solenoid. You can wire it all with pretty short wires in the engine compartment.

For a normal 4 or 5 pin cube relay, mount it next to the battery/junction box. Wire one side of the relay coil, pin 86, to ground, and move the starter solenoid wire to the other side of the relay coil, pin 85. The relay should now click on when you try to start. Wire the relay contacts pin 30 to +12v on the junction box and pin 87 to the original starter solenoid tab. (Note: if it's a 5-pin relay, pin 87a remains unconnected.)

The wire to the relay coil can be any gauge you want - they're only carrying ~0.15 amps. For the relay contact wires (+12v and solenoid), I'd do 16 gauge but 18 will be fine, if it's all you have, since the distance is so short.

There's a picture here of doing the same sort thing to add a headlight relay to early 240s:

(I wouldn't add a fuse to either circuit since headlights and starter are pretty critical circuits. Just make sure you've wired it correctly before reconnecting the battery.)
Yup, all that is in the other thread as well. I actually mounted my relay on the intake manifold support bracket. Wires are maybe 6" long, nicely tucked away, and everything is fed straight from the starter as well.
Popping this thread back up after 6 months because I've finally gotten around to installing this relay. It's gotten to the point that dispite having a perfectly healthy fully charged battery I can only get the car to start if I just it with a secondary battery.

I got it installed and it seemed to work like a charm, except the starter in firing as soon as I go into key position II and continuing to running until I put the key back to pos I. Not sure if I have things wired wrong or the relay I have it stuck on.

Here is how I wired the relay
Pin 30 - Constant 12v
Pin 85 - Starter Solenoid wire
Pin 86 - Ground
Pin 87 - Starter Solenoid Pin

Can anyone confirm if I have done anything wrong?

^^^ that seems correct to me. What exactly was the original problem? Maybe it's an ignition switch issue, and not the starter?
Yeah pretty sure it is the ignition switch. My starter was rebuilt last week at a local shop and my battery was tested yesterday showing perfect health.

With the new relay installed this is the first time I've been able to get the starter going without additional help. Only its cranking on position II rather than III now.

Prior to the relay install, I would get the typical stuff happening on pos II and only a click from the starter on pos III followed by everything going dead. I would need to disconnect and reconnect the battery before I could attempt to start again.
Do you have a test light? If so, unplug the original starter solenoid wire from the relay and probe it with the test light (other side to ground). See if the test light glows faintly when the ignition switch is on, and brightly only when in the start position. It should stay off completely other than when in the start position.
I won't be able to test this until I stop back at my parents' place where my car is parked hopefully tomorrow. What would be the fix if the Test light is glowing in pos II? New ignition switch? Is there another work around?

Thanks so much for the help!
As a temporary fix, you can wire in a push button switch to engage the starter. I don't have a 940, so I'm guessing on what would be easiest. Since you have the bypass relay already, all you need to do is wire a switch that energizes the relay coil when pressed.

The simplest would be to disconnect and tape-off the original starter solenoid wire, then run a pair of wires (speaker cable would be fine) to a switch in the cabin and connect the ends across +12v/30 and coil/85 at the relay. This will run the starter when pressed regardless of the key position. A better setup would be to wire to switched +12v somewhere other than the relay. Since the relay draws very little power, pretty much any switch and any gauge wire will be fine. Without the key on, pushing the button will crank the starter but the engine won't start due to no power to the injectors/ignition/ECU/etc. OK, does this all make sense?
Here is how I wired the relay
Pin 30 - Constant 12v
Pin 85 - Starter Solenoid wire
Pin 86 - Ground
Pin 87 - Starter Solenoid Pin
So, this way?
Blue/green now triggers the relay, instead of the original path to the solenoid (dotted line).

As a temporary fix, you can wire in a push button switch
= Replace the original blue/green from the key with your powered push button wire of choice.

I have two 1991 740s. The starter circuit has failed in BOTH vehicles. Im gonna rig up a relay

For a temporary switch, I would run FUSED Powe to the relay control circuit terminal and then a ground for the other half of the circuit into the cabin. It's just a little better than running a long power wire or tapping into cabin power circuits
Interesting discovery today… scrap all this, turns out the brass battery disconnect adaptor I have been using was all oxidized and therefore not making a strong enough connection on the negative battery terminal. I’m happy that it ended up being a simple problem to fix, but I could only laugh at myself for how dumb I was in overlooking it.
Quick clean up with a small wire wheel and some anti oxidizing compound later, I’m back up and running

So yeah, make sure you check allllll your connections. Some how I overlooked the most important one