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MG MGB Technical - Testing Gauges?

Is there a way to test the engine gauges without taking everything apart? i.e. apply some amount of volts to the gauge.

I recently bought a 68 BGT and I am just about ready to start it for the first time. I disconnected the coil and cranked over the engine many times to try and build oil pressure but it never showed any. I also put 5 gal. of gas in, so the gauge should show a little over 1/3 but also nothing.
Steven J. Korotky

Steven, You can remove the green/black wire from the gas tank sending unit and ground it with the ignition switch on, gauge should go up if it is working. The check is best done with an assistant as you want to ground it only long enough to see if it works. On 68 cars only the wiring diagram shows the oil pressure gauge to be fed from the output of the voltage stabilizer, my 68 was is as shown in the wiring diagram. The output of the stabilizer is a varying voltage that may average around 9-10 volts. The output is a green wire on the 68, or it is on may car and the wiring diagram shows it as green. It changes to light green/green at the fuel gauge and is sent to the oil pressure gauge from there.

Based on what you are telling us you probably have a bad voltage stabliser.

The best way to be sure about the oil pressure is to buy a cheap mechanical oil pressure gauge and hook it in place of the electrical oil pressure sending unit.

Good luck, Clifton
Clifton Gordon

Check out Paul Hunt's web site. www.mgb-stuff.org.uk, I believe or just do www search for Paul Hunt Solihull. He has a gauges schematic in there to click on and descriptions and diagnostics. It's under Spanners then Electrics then Gauges.

J.T. Bamford

My oil pressure guage needle suddenly dropped
one day soon after an oil change - and it sent my
hair straight up.

"Thwacking" the sender with my finger immediately
resurrected it.

Must've been a loose electrical tab.
Daniel Wong

Oddly, on UK spec cars, even the 1980 GT still has a mechanical oil pressure gauge. On starting mine, it registered nothing but that was down to plumbing it into the wrong tapping! Also, I had disconnected the multi-plugs by the steering column to get better acces when refitting the pedal box and forgot to reconnect so when I first connected the battery, everything was dead!
FWIW
Martin

Sometime in the early mid 70s, MG went back to the mechanical guage, which looks just the same as the electrical one of the 68-7? cars that preceded it.

Being cheap and not wanting to pay what I considered an exorbitant amount for a new sending unit, I chose to get a good mechanical gauge out of a junker and put it in my 68 GT. I have not regretted doing that. If you choose to take this route, do make sure you get the pipe interconnector off the firewall and replace the flex hose with the new steel braid/teflon hose that Moss and others sell. FYI
Bob Muenchausen

"Must've been a loose electrical tab. "

If all you did was "Thwack" the sender with your finger then you *still* have a loose electrical tab ... (Present Owners, doncha hate'em).

The UK kept the dual mechanical gauge until it got the separate mechanical oil gauge and electric temp gauge in 76, shortly before the NA cars got the mechanical oil gauge in 77.
Paul Hunt

This thread was discussed between 25/08/2003 and 28/08/2003

MG MGB Technical index

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