You could use one of these:
http://neksiwel.20m.com/photo5.html

----- Original Message -----
From: "Daniel L. Katz" <katzd54@YAHOO.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Tuesday, April 28, 2009 9:37 PM
Subject: Re: [VANAGON] O2 Sensor?

> O2 sensor should remain connected and be up to operating temp for
> monitoring output voltage. a high impedance volt meter (i.e., most digital
> meters) must be used.