Voltage to contactor drops out....hence relay opens...it does this repeatedly. Any ideas? Thanks

On a E825 2002 I am trying to find the cause. I measure the v. (72) when the key and brake switch are active, but then 72 goes to 0 on the coil input. It will drive for a short while sometimes, then it will click on and off like a metronome. What powers the coil? Has it got some electronics between the manual switches and the coil terminals?\

Any help would be appreciated, thanks

No electronics on the line side.
Are you sure that you are not checking the controller side of coil? The controller side goes to 0v when energizing contactor.

The main contactor is run by the controller. Could be a loose input wire on the connector or the relay on the key switch circuit. Apparently these key switch relays are not the most durable. After checking to make sure your input wires to the controller are seated properly, to the right of the main coil there is the flasher module, to the right of that there is, top to bottom, 3 small components: buzzer, key switch relay, timer. There is a gray/white wire and a white wire on the bottom edge of the relay. Unplug them and jumper them together. That should send send constant power to the controller on the key on circuit. So long as the contactor disengages when you turn the key off, I’ve been told it’s ok to leave it jumpered.

Check parking brake switch adjustment and connections

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Agree with the brake switch adjustment, but if thats not it check the start key switch, and don’t use heavy key chains.

Thank you, I will check all and jumper…I’ll let you know.

I did some checking…the brake switch seems ok, the key switch seems OK, I have not checked all yet, but timed the drop out of the coil voltage…23 seconds, reliably, unless I hit the throttle, then it stays on for a bit…sometimes. Coil is very hot when it is on.

To see if it’s the high side or low side dropping out. Connect a jumper wire from a reliable B+ 72v source to + side of coil.
If it still cycles, the controller or pin & wire 11 may be faulty.
Or coil has shorted turns drawing to much current. T4 has a code for that. T2 may not.