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MG MGB Technical - sender unit

i have a mgb 64/65 model with chassis number GHN3/53843.
My sender unitBHA 4471 is not usable, due to a big leak from the body.The gauge is a smiths.
Am wondering if i could use the earlier senderBHA4292,which used a Jaegar gauge, with my smiths gauge.
any suggestions please, as i am desperate.
vignes pillai

Hi Vignes - unfortunately not directly. The sender and gauge combo changed from the Jeager type to the Smiths type in October 64, and the operating characteristics of the two systems are reversed. But unfortunately they only changed the way the sender attached to the tank - from screws to a locking-ring - in March 65. This left a small number of cars with an intermediate sender BHA4471E using the new system but the old method of attachment, and that has been NLA for years.

You could get use the earlier sender but would also need the earlier gauge to go with it, and bypass your instrument voltage stabiliser.

However you can keep your existing gauge with the old sender BHA4292 using an intermediate module between sender and gauge which performs the required reversal, from the likes of Spiyder -

You could also use the later tank and sender, but the fixings to the floor are completely different i.e. a bigger job.

Thanks a million PAUL. have ordered the earlier sender unit BHA 4292 and the Gauge wizard.
vignes pillai

Let us know how you get on, I came across these a long time ago but haven't had the opportunity to try it out.

Hi Paul
I will :
should get to you once i get the parts from uk.
could you please tell me the resistance of the fuel sender when empty and full, for the BHA 4292 SENDER
vignes pillai

No experience myself but according to this it ranges from 0 empty to 70 ohms full.

I'd be interested to have that confirmed.

I fitted the gauge wizard to my MGA because the fuel sender units presently available are just not accurately made. The MGA gauge is particularly sensitive to this and even though my new sender unit has a resistance range of 0.5 to 72 ohms (instead of the correct 0 to 70 ohms), this still meant that even when the tank was empty,the gauge never dropped below 1/4 full.
The MGA pre-set in the Gauge-Wizard didn't work for my car and I had to go through Spyda's recommended procedure of draining the tank, then re-filling it in 1/4 tank steps so that you can calibrate the sender with the gauge. It is a bit tedious but it worked perfectly.

My brother in law bought a Gauge Wizard for his 77 MGB and he found that the MGB pre-set didnt work for him either. We plan to go through the tank filling procedure on his car to get it working.

I posted this on the MGA Forum earlier this year and this is a copy of the post.

"Thread: [b]Gauge Wizard[/b]

Originally posted 13 July 2018 at 22:57:49 UK time in the MGA Forum
Colyn Firth, South Yorkshire, United Kingdom

"I fitted a new fuel sender unit a year or 2 ago which was a vast improvement on the old unit because its resistance range was almost correct.
Its resistance range is 0.5 to 72 ohms which is really close to the correct range according to MGA Guru) of 0 to 70 ohms.

The old sender unit had a resistance range of 15 to 98 ohms which meant that the gauge showed full most of the time and dropped to about 1/3rd full when the tank was empty.

The new sender unit was much better in that the gauge did drop to about 1/8th full but would never quite drop to empty.

The trouble was that I started to trust the gauge a lot more than I did before which was a mistake, I normally keep an eye on the odometer to see how many miles I have driven since refilling the tank and doing this combined with an eye on the gauge has worked fine.

However, if you have ever attended any of the MGCCs MGA Weekend Tours or similar, you are often told to zero your trip at a certain points so that you can follow the route.
This meant that it is really easy to lose track of your actual mileage and this meant that I ran out of fuel on the way home from 2 of these events!

So a few months ago I bought Gauge Wizard (From Spyda) to see if its digital processor would let me correct the gauge so that it read correctly.

I had read about it in Safety Fast Magazine when the MGA Scribe Mr Edward Van Dyke wrote about the Gauge Wizard by Spyda. He had arranged with Spyda to include the MGAs sender unit (0 to 70 ohms) to be included in its range of built in pre-programmed range (or Pre-Sets)
This means that you install the gauge wizard, select the MGA pre-set and off you go.

Well, its no surprise to know that using the pre-set, my gauge didnt work any better than it did before!

So I had to then go through the Spyda recommended procedure of filling the tank in 2 1/2 gallon steps and programming the gauge wizard each step of the way.
You start with an empty tank and work your way up to the tank being full.

It is a bit tedious and I must admit that I was not totally comfortable with the process as you have to handle a lot of fuel to do this. (In did keep a couple of heavy duty fire extinguishers handy.)

You have to input the sender units output to the gauge wizard in 1/4 steps, from empty through to full so that it remembers each setting.

Then you programme the gauge wizard to move the gauge needle to match the newly memorised settings from the sender unit.
This means that when the sender unit sends empty, the needle also shows empty and when the sender unit send full, the gauge then also shows full. etc

At first I was unsure if there was any real improvement, the gauge showed full for longer than I expected. But this was because when I checked the resistance reading of the sender unit on the 3/4 full mark, there wasn't so much difference from the full resistance reading.

However, once the fuel level dropped, the gauge began to show much more accurate readings.
I found that when the gauge showed 1/2 full there were exactly 5 gallons remaining in the tank and when the gauge showed 1/4 full there were exactly two and a half gallons remaining.

I have also installed the warning light option to act as a low fuel warning light, this illuminates continually when the needle drops to the 1/4 level and then flashes when the needle drops to 1/8 full.

It is a refreshing change to be able to look at the fuel gauge and know that what you see is what you have really got! "


The instructions that came with the Gauge Wizard are no so easy to follow and so I used their YouTube video to write out my own version of the instructions in a simpler format for both the MGA and the MGB if anyone would like a copy.

This is the link to the Gauge-Wizard Post I put on the MGA Forum.

Colyn Firth

Hi Colyn
would be happy to receive your version of the instruction for the Gauge Wizard, i have difficulty with electrical jargon.i am waiting for my order to arrive
vignes pillai

Hi Vignes
send me your email address and I will send you a copy of my transcript of the Gauge Wizard instructions for the MGB.

Colyn Firth

This thread was discussed between 14/11/2018 and 17/11/2018

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