SW Electric Oil Pressure Gage Issue

[Griff]

I'm just now putting in my aftermarket SW gauge cluster in my 69 Roadrunner. All is wired up correctly and I had a friend double check as well. When I start the car, oil pressure gage pegs at 100psi. I know the car runs at a steady 33psi on a good mechanical gage that is made just for checking oil pressure, (not for mounting in a car). I had that gage zip tied to the cowl for the winter while I was breaking in motor and running engine over the last few months.

Sending unit, (which is an after market "bell" shaped electric gauge, that is not SW branded), but bought new from Mancini. With car running, I can take sending unit wire off, gauge drops to zero. Then, I can ground that wire to block it again pegs to 100. Repeated this a few times, same results.

I checked to make sure sending unit wasn't grounding itself to block (72 - 440).

Any help would be appreciated.
Thank you

PS - The gauge cluster was bought used and I was assured all worked. Temp and alt gauges work perfect.

 

[BLK 68 R/T]

Probably has the wrong resistance between the gauge and sending unit to read correctly.

 

[Sixpactogo]

I would suspect the send unit is shorted or wrong. Are you using a idiot light sender to run a pressure gauge?

 

[Griff]

Probably has the wrong resistance between the gauge and sending unit to read correctly.

My friend was thinking that as well, does that mean I would have to purchase the SW electric sending unit?

 

[Sixpactogo]

My friend was thinking that as well, does that mean I would have to purchase the SW electric sending unit?

No necessarily......But you do need a sender for a gauge, not a light.

 

[Griff]

I would suspect the send unit is shorted or wrong. Are you using a idiot light sender to run a pressure gauge?

No, it's the large "bell" shaped sending unit (not SW branded specific), bought for about $25 from Mancini

 

[Griff]

Probably has the wrong resistance between the gauge and sending unit to read correctly.

If this is the problem, what can I do to correct that? Can the gauge be re-calibrated or do i need a specific electric gauge sending unit?

 

[BLK 68 R/T]

You have confirmed the sending unit is not internally grounded to the block and the gauge works by grounding the wire. In order to make it read correctly the only thing I know of is adding a resistor in the wire. Or get the corresponding sending unit that is compatible with your gauge.

 

[Griff]

You have confirmed the sending unit is not internally grounded to the block and the gauge works by grounding the wire. In order to make it read correctly the only thing I know of is adding a resistor in the wire. Or get the corresponding sending unit that is compatible with your gauge.

Ya, I think I may have found the answer over at the "Jalopy Journal" and "Chevelles" site. It looks like there is a few different sending units for the various SW oil pressure gauges. Most common: the 0-80psi gauge and the 0-100psi gauge (which I have). I'll have to check in the morning on which sending unit I have (if there is a number on it).
But it looks like the 0-80psi unit (gauge number 82304) uses the SW 279A. The 0-100psi gauge (82305) uses the 279B-F sender unit.

Stewart Warner Sending Unit Question.
Are There Different Electric Oil Pressure Gauge Sending Units?

 

[Griff]

Thanks guys!

 

[Black_Sheep]

I would suspect the send unit is shorted or wrong. Are you using a idiot light sender to run a pressure gauge?

SW’s website lists the ohm values for senders in their troubleshooting section. I think Sixpactogo nailed it…