Possibly a nieve question about diodes

[Alex_Blackwood]

Perhaps some of these links may be of use. I would be inclined to have a word with the DVE people.

http://www.icpltd.co.uk/pdf/simplavolt.pdf

http://www.suregripcontrols.com/install_suppress.htm

http://www.directvehicleelectrics.c..._diode_24_volt_072776_A_type_termination.html

Just a couple of questions. You have by fitting a relay obviously transfered the original problem from the pressure switch to the relay. What is the current rating of your pressure switch? If high enough it may be possible to dispense with the relay and fit a suppressor direct to the switch.
Also Do you need such a powerful pump for your system? perhaps it would help if a smaller pump was fitted.
Having said all that. As you have the system set up I would be inclined to look at the DVE relays with diodes.
Good luck!
Alex.

Sorry. I must correct my glaring error. The relays in the direct vehicle electrics link have the diodes across the coil. Whilst fine for protecting the pressure switch contacts, the OP also needs a diode across the motor input as has already been suggested. My fault for trying to rush on a Sunday morning!