SOLENOID

85 Commando--solenoid.
There is a black heavy wire to starter and another to (-) of battery.
Does anyone know which wires connect to the positive and negative terminals
on solenoid? Also, is there a red ground wire and where does it attach to solenoid?
I have loose red/white and purple/white wires.
Confused.

'75'? (850?) Commando solenoid?

If you have the original Prestolite solenoid?

Then the heavy starter wire connects to the left-hand large terminal (looking at the solenoid as it is fitted in position) and battery Neg. to the other terminal. The red/white (from the starter button) connects to the small stud with a spade on the left side marked 'S' on the casing. The purple/white (ballast resistor bypass wire) connects to the other spade marked 'I', although if you have an electronic ignition fitted then the purple/white should not be connected as it has no function.

There is no ground wire connection on the solenoid (even though the wiring diagram appears to show one).

ELMOWHITE said:

Also, is there a red ground wire and where does it attach to solenoid?

Click to expand...

If you have a loose red wire with a female spade terminal?
Then it is probably the 2MC emergency starting capacitor (blue can on a coil spring next to the solenoid -but may not be fitted?) ground wire connector.

If the red wire has a ring terminal?

I noticed my own 850 Mk III has a red ground wire with a ring terminal connected under one of the side panel rear bracket mounting bolt heads so perhaps that is the one you have?


Or it could be the original red harness ground wire that connected to the battery Pos. terminal. However this harness red wire should not be connected to the battery (if it is intended that the electric starter will be used?) but taped up out of the way, connected to the frame or removed.

When I built my MK3, I found that I did have to fit a ground wire to the solenoid, otherwise it would not work! I don't know if others have found this to be the case also?

The case of the solenoid is grounded (earthed). This usually has a red wire from one of the case bolts to a good grounding point.

Reggie said:

When I built my MK3, I found that I did have to fit a ground wire to the solenoid, otherwise it would not work! I don't know if others have found this to be the case also?

Click to expand...

There does appear to be a red harness wire with a ring terminal included with the other solenoid wires on my own Mk III, although fitting it to one of the solenoid mountings would be more awkward than one of the side cover bracket bolts (as it is on my own Mk III).
The wire is fairly short and the solenoid top mounting plate fittings are not particularly accessible without removing the solenoid.

L.A.B. wrote;

The wire is fairly short and the solenoid top mounting plate fittings are not particularly accessible without removing the solenoid.

Click to expand...

That was the case with mine, so much so that I doubt that I could have got the ring from the harness fitted to the solenoid as there wasn't enough slack, so I mounted the red harness ring terminal to the nearside mudguard bolt ( next to the side panel bracket bolts), and made another connection (ring) from this bolt to the upper mounting bolt on the solenoid. A bit messy but it works.

Reggie said:

I mounted the red harness ring terminal to the nearside mudguard bolt ( next to the side panel bracket bolts), and made another connection (ring) from this bolt to the upper mounting bolt on the solenoid. A bit messy but it works.

Click to expand...

The solenoid mounts to the frame, so there should (theoretically) be a direct earth return path back to the battery through any other frame mounted earth wire connection, (via the engine cases as there should be a direct frame to engine earth/ground connection) even without the red wire at the solenoid, provided all the bolted connections are making good electrical contact (no paint or rust?). Although I would agree that it certainly does no harm to have some additional earth wires.

The solenoid on my own Mk III still works with the red (solenoid?) wire disconnected.