reverse polarity

[plumbers crack]

Do they make reverse polarity guages??? My buddy just changed out 2 guages (oil pressure) and when he started the boat up the guages are going backwards!

[glassdave]

I would look at the wiring first. Thats odd, gotta have something crossed in there somewhere. Are they the same gauge as what came out?

[MERPerformance]

I would look at the wiring first. Thats odd, gotta have something crossed in there somewhere. Are they the same gauge as what came out?

I agree, something is switched, maybe the sender is on the ignition terminal and the ignition is on sender terminal side. If the ignition was on the ground terminal it would blow the fuse.

[inbetween]

I've heard some of the VDO gages used different senders. Use a VDO sender with a different brand gage and the gage works backwards. (Or VDO gage with a diffeferent sender also)

[Tony]

Is it a Baja, if so its normal. When you hit the trim switches the fuel guage should go up and down too. J/K.

Pull the sender wire off and see if the needle bumps to zero when you turn the key on/off. If so you probably have the wrong wire on the sending unit.

[Chris]

Pressure and level gauges are just calibrated ohm meters. The sending units are variable resistors. But some go one way and others go the other. For example, on some brands, the sender increases impedance as the pressure rises and others decrease impedance. Gotta' match the sender to the gauge.

[plumbers crack]

Problem solved,my friend changed his senders,problem was he changed the wrong senders which are oil activated(complete circuit) which are for his electric chokes I believe he ordered the wrong ones and just reordered the right ones @50 bucks a pop.He had hp 500 carb mercs. Thank you for the replies!