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Old 06-12-2010, 01:00 AM
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Rzeppa Rzeppa is offline
Cruise Moab Chairman & RS Secretary
Join Date: Aug 2005
Location: Kittredge CO, USA
Posts: 6,633

Originally Posted by CardinalFJ60 View Post
I pulled the cluster out of the 40 to re-do the lights and other general spruce up things. the Oil pressure gauge has never worked. I put in a new sender and used gauge while ago and still no workie. While it's out, I'd like to test things from the cluster back to the sender.

How do I bench test the gauge?

I looked in the FSM and it shows how to test it when still hooked to power in the vehicle. I need to do that test on my bench, but don't know how/where to get power to it with my extra battery.
Hi Shawn,

The oil pressure gauge is basically an ammeter. It is connected to system + on one side and to the sender on the other side, the sender is grounded on it's other side. The sender will give less resistance to higher oil pressure, and thus deflect the gauge.

The coil inside the gauge is fairly sensitive. If you connect 12 volts across the terminals without the sender to limit the current you will fry it instantly. Like a fuse.

To check it on a bench you will need a DC power supply and some kind of current limit in series such as a power resistor of similar ohms as mid point of the sender's resistance. I'd look it up but my manuals are in the garage, and I'm not. My guess would be that the sender's resistance would be on the order of 50-200 ohms, because that would be a typical value for the sensitivity of our gauges. Beware of using a potentiometer to simulate the sender! If it is all the way to one end it will be a short and you will fry the coil! If you do use a potentiometer to modulate the current, always start at midpoint to avoid that.

Rather important to observe proper polarity on the bench test: these mechanical gauges can be easily damaged with reverse polarity applied to the terminals.
Jeff Zepp
Kittredge CO USA
1971 & 1976 FJ40s, 1978 FJ45, 1987 FJ60
Rising Sun 4WD Club, TLCA #4063
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