TR4/4A Voltage Stabilizer question.

[mtlman8]

Today I went for a drive and had no temp. or fuel gauge. I noticed two wires came undone on the voltage stabilizer, so I put them back, and still no movement. are the wire positions specific on the stabilizer? BTW. I have a full tank of gas and I wired in a new electric fan. fuses are all good.

 

[TR3driver]

Yes, it has a definite input and output. IIRC the input is marked with a 'B', the output 'I'.

 

[Got_All_4]

Bypass or jump the stabilizer and see if you have full fuel and max temp. If so the stabilizer is the problem.

 

[mtlman8]

Thanks Randall!

 

[dklawson]

Bypass or jump the stabilizer and see if you have full fuel and max temp. If so the stabilizer is the problem.

Not quite. Bypassing the stabilizer passes full system voltage to the gauges which makes them read "higher" but not "max". If the stabilizer is working and you short the sending unit wires to ground, then the gauges should go to full/hot (max).

As Randall said, the connections are "I" for "instruments", "B" for "battery". AND (this is important), the mounting tab on the stabilizer must have a good ground connection. If the ground is missing the stabilizer will pass full system voltage to the gauges which will make them read high.

 

[Marvin Gruber]

Good info Doug! I'm still dealing with a high reading on Fuel gauge in a MGA thats been modified.

Marv

 

[mtlman8]

I have'nt done anything today, but both gauges are at zero. they were working perfectly before I noticed they came unplugged.

 

[mtlman8]

So if I put battery wires to battery and ground the sending unit wires they should read FULL hot?

 

[dklawson]

Good info Doug! I'm still dealing with a high reading on Fuel gauge in a MGA thats been modified.
Marv

However, the MGA won't have the voltage stabilizer. BMC didn't add them until about 1965 a couple of years into MGB production.

The high reading on the MGA gauge may be down to just needing calibration. Barney Gaylord has a great series of pages on his MGA-Guru web site that explain how the earlier gauge system works and how to calibrate it. Start with the web link below then read forward using the green arrows at the bottom of each page. He introduces the gauge then moves on to repairs and calibration.
https://mgaguru.com/mgtech/electric/fg_01.htm

 

[TR3driver]

So if I put battery wires to battery and ground the sending unit wires they should read FULL hot?

Yes, but that's not really a good idea. Inside the gauges is a little heater, designed to run on 10 volts or less. Hitting it with 12.6 volts from the battery may not sound like much, but it produces over half again as much heat and can damage the gauge.

If you must do the test, just brush the wires together long enough to see the needle head for the stop.

As noted, the original MGA gauge used a "balanced" movement, not the "hot wire" found on TR4 and later TRs. The balanced movement actually reads backwards, grounding the sender wire should cause it to read empty (so the problem might be a bad connection between the gauge & sender, or a bad ground on the sender). But the car might have been modified with a later gauge. I'm not sure offhand if all MGB used the "hot wire" movement, but most of them did.

 

[dklawson]

I'm not sure offhand if all MGB used the "hot wire" movement, but most of them did.

Not sure it's worth going into details here on the Triumph part of the board but early MGB up to about '65 used the same gauge types (including mechanical tach) as the MGA. As I mentioned above, BMC added the stabilizer later than Triumph.