MGB & GT Forum

I've found lots of discussions on brightening the dashboard lights by bypassing the rheostat (mine's a '79 B). But I can't find any directions on how to do it. My switch has 4 wires connecting to 3 terminals. One red/green then one with two red/white and then a single red/white. Do I just need to connect the red/green to the three re/white?

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Mike A

Here is the MGB Wiring Diagrams by Auto-wire. I think your car is close to diagram on sheet 32. You should have a red green wire coming in, and three red white on the output. You can run all four wires together to bypass the rheostat. For some years, at least on the NA cars, they simply put in an on/off switch.

I have a steel dash car, and mine is still connected, even though I converted to LEDs last year. The rheostat is meaningless for dimming the LEDs, but it works as an on/off switch. However, I've never turned them off.

Replace the dimmer with a toggle switch or just jumper it and remove the dimmer.

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Basil C. Adams
1956 MGA Coupe (Show Car)
1957 MGA Roadster (Driver)
1958 MGA Coupe (Racecar)
1959 MGA Coupe (unrestored)
1960 MGA Coupe (unrestored)
1960 MGA Roadster (Driver)
MKIII Elva Courier (E1056)
1967 427 Cobra
1972 Alfa Romeo Montreal
A coupla late MGBs
1960 Austin Healy BN7
More Cars than Brains

Though for many the dimmer is useless, if it does work:
a) Keeps car in "better" (more OE) condition.
b) Will prolong bulb life, (turn off during day), though admittedly they last a long time.
c) As well, when it comes time to sell, any new to MG person would not know so many are frozen, and this not working might lead them to wonder what other hidden problems there might B. Could be a simple fix.

I fixed my fully stuck on dimmer (/80) by removing it, then squirting Electronic Control cleaner in back hole and 24 HOURS LATER WORKS LIKE NEW! The only bulb too dim was on Speedo, because I couldn't read my trip meter. I added a single E-10 LED to speedo. I can dim LED about 25% before it cuts out. - Works for me.

I glad I'm able to dim, for again recently, driving in dark wilderness across Vancouver Island, there are a couple of places when driving 45 MPH, you'll bottom out (Ouch!) By dimming, I was able to see the (barely visible) road dip approaching. As well, any animals at side of road, their reflected eyes are not diminished by bright dash lights. Fix if you can. Add LED where needed.

Add 7A inline fuse.

To remove knob, (like many others), there is a tiny ball bearing at end of spring on shaft you must push in.




Add a 7A in-line fuse to circuit.

X2 on the 25% dimming of LED output via rheostat.

Yes.

The red/green wire is the power, the red/white wires go to the gauge lights.

Cheers,

Rick

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If I could get all the money back I ever spent on cars. . . I'd spend it on cars. - Nick Mason (Pink Floyd)

There was nowhere to go but everywhere, so just keep on rolling under the stars. - Jack Kerouac

Coddiwomple (v.): To travel in a purposeful manner towards a vague destination.

The journey is the destination.

X2 on keeping it in, although the effectiveness for dimming LED's depends on the type being used.

This 25% estimate is correct for Lionel 5 SMD E10 types, but my later, brighter torch type LED's can not be dimmed as deeply. One solution is keeping the bulb in the cigarettelighter in or even adding another bulb for a higher loading on the circuit. In fact the rheostat max resistance is too low for LED use, it does not bring the voltage down enough (when exchanging bulbs by LED's one by one over the gauges, each LED added, reduced the adjustment range one more step is my experience)

I was able to bypass the rheostat but it sure doesn't seem to improve the brightness much, if at all. Bit I'm also wondering if my benchmark was AFTER I broke the rheostat trying to get the knob off. I thought maybe it was threaded and turned it hard enough to break it. Good news is that I now know how to properly replace the knob when the new one comes in.

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Mike A

I was able to bypass the rheostat but it sure doesn't seem to improve the brightness much, if at all. Bit I'm also wondering if my benchmark was AFTER I broke the rheostat trying to get the knob off. I thought maybe it was threaded and turned it hard enough to break it. Good news is that I now know how to properly replace the knob when the new one comes in.

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Mike A

On my '76 I plugged both wires onto the same side of the rheostat. But they did not get any brighter until I installed a headlight relay kit.

David