It could be that the pump had a problem that caused it to draw too much amperage, therefore; someone unplugged it.

Pulling a vacuum with your miteyvac, is a good place to start. See if you can pull a good vacuum on it. If you can, and it holds, that could indicate the pump. You can also test the pump to see if it pulls a vacuum, just be hooking the miteyvac directly too it, and plug it in. the gauge will indicate if it can pull a vacuum.

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1959 Gravely LI, 1963 Gravely L8, 1973 Gravely C12
1982 380SL
1978 450 SEL 6.9 euro restoration at 63% and climbing
1987 300 D
2005 CDI European Delivery
2006 CDI Handed down to daughter
2007 GL CDI. Wifes