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MG MGB Technical - Electrical Probelms, Directional & Fuel Guage

I've got two electrical issues and I would appreciate some suggestions.

1977 MGB, finishing up refurbishing, hasn't operated fully yet, so these may be long term issues.

Directionals, basically don't flash most of the time when the lights are on. Changed out flasher, same thing happens.

Fuel Guage, doesn't register. Tested voltage coming into the guage, seems to read OK when not connected. At soon as I connect the green/black to the guage the voltage drops... doesn't register. I'd suspect the guage but I've got another and the same thing happens. Also, both guages read "full" when connected directly to 12 volts.

Thank you in advnace for any assistance.
Brian Denis

Brian - Do you also have a temperature gauge that is flakey? If so, then your voltage stabalizer is bad. If the temp gauge is operating ok, then I would start looking looking at the wiring on both side of the gauge, especially the connectors. If the connectors are corroded, they will cause the voltage drop that you are seeing.

Your directionals are very sensitive to voltage. Make sure that all connections in the circuit are clean and making good connection. Make sure taht all ground points are making good (read perfect) connection. For more on ground point preparation, read my article at: http://www.omgtr.ca/technical/General%20Technical/grounding.htm
Next, make sure that all the light bulbs are the proper ones and preferable made by the same manufacture (or at least are not some no name cut rate bulbs).
Good luck - Dave
David DuBois

I agree that the likely cause is the voltage stabiliser - you may have a non electric temp guage and if so then that will not be affected.

Re the indicators - don't mess about, just swap the old two terminal flasher unit for a more modern three terminal one that is rated for 4 x 21 watt bulbs. The extra terminal goes to ground and the unit is electronic and not subject to voltage variations. You can buy these at your local autoparts store or pocket one in the wreckers yard!
Chris at Octarine Services

Hi Brian


'don't flash most of the time when the lights are on' suggests an earthing problem, as the earth is the common factor in the main lighting and indicator circuits. The headlamp earth (which I think is bonded to the body by the bulkhead, black wires) is prime suspect.

HTH.. Don
Don

Thanks David, Chris & Don for the ideas so far, I'll look into them all today.

Two additional pieces of information.

The turn signal assembly is mechanically worn / unstable. The lever is "floating" alot, particularly high to low beam. Actually last night I had to cancel the first nightime drive because I couldn't get the high beam off and the left side headlight and front running light were off. Previously all lights were operating. I have another lever assembly that I will install today.

All other gauges operate fine, including the temp gauge.

Re-reading my original post... either I need a "spell check" or to stop posting between innings of the Red Sox games!

Thanks again.
Brian Denis

Chris @ Octarine Services wrote:

"...just swap the old two terminal flasher unit for a more modern three terminal one that is rated for 4 x 21 watt bulbs. The extra terminal goes to ground..."

Chris,

A quick note for our US enthusiasts: I'm not familiar with the 3-terminal flashers you have in the UK, but grounding the third lead with a US spec flasher (type 550) is a definate NO-NO! Here in the US, the third terminal is used to operate an indicator lamp, and is hot when the flasher is operating. Shorting this terminal to ground would release a lot of the valuable smoke from inside the flasher!

The 3 terminals on a 550 are

"X" this terminal is the power input terminal

"L" this terminal is the power to the turn signal lamps via the TS switch.

"P" this terminal is for the indicator lamp("P" is for "pilot" lamp?).

When using a 550 as a TS flasher in an MGB, the "X" terminal would get the green wire from the old flasher, and the "L" terminal would get the lg/n wire. Just ignore the "P" terminal.

Another note of interest to US owners concerning 3-terminal flashers: Many of the newer ones are made incorrectly. Typically, the 550 flashers are the ones we use, but the newer ones from some makers are made so that the third terminal is ON when the flashers are OFF - not good! That means that the hazard indicator is on all the time during normal driving. If we want to use a 550 for the flasher function, buy a Triton 550 in the "short" can. The Tritons in the "long" can are incorrect, as are many other brands.

For the US folks, you can replace the Lucas 2-terminal flasher with a type 552 flasher from the auto parts store (about $2 cheaper than a 550). It is in reality a hazard flasher, rather than a turn signal flasher (as is the type 550), so the signal lamps will still flash even with bad circuit connections.
Dan Masters

The problem with using a hazard flasher in place of a standard flasher is that they are designed to be insensitive to the current draw through them. This means that they will flash the same rate if you have one bulb hooked to it or a dozen bulbs or no bulbs. Bottom line, you will never know if one or all of your indicator bulbs are bad. The standard flashers are designed to flash at a given rate for a set number of bulbs connected to them (usually 2) and will flash faster if more than two bulbs are connected or if there is a short to ground in the system, or will flash slowly or not at all if one bulb is burned out, thus letting you know that there is a problem with the indicator circuit. Cheers - Dave
David DuBois

You must have electronic flasher units in the US, surely. Ford fits them to UK cars.

Perhaps someone over there can advise other part numbers but the Lucas 19FL is the one I normally use.
Chris at Octarine Services

"You must have electronic flasher units in the US, surely."

Yes, we do. They cost about twice as much as the standard, offer no significant advantage, and operate the same way as the standard units. Grounding the third terminal will still smoke the unit.

They are a one-to-one replacement for the 550/552 units, and have the same input/output connections.

That is for replacement items off the shelf at our local auto parts stores. With a little research, I'm sure a wide range of options from OEM applications can be found, but for the most part, they'll either be the same as the 550/552 types, or they'll not be a "plug&play" for an MGB. Each OEM unit would have to be evaluated for the proper connections. A blanket statement to "ground the third terminal" could lead to disaster.

David,

You are right about the operation of a hazard flasher, and it is this characteristic that makes them suitable for a "quick and dirty" fix for turn signal problems. Even with bad connections and dirty switch contacts, they will still operate the turn signals, but they should be considered only a temporary fix until the real problems can be cured.

However, they can still be used on a permanent basis as long as the owner remembers to do a visual check of his turn signals on a frequent basis. At $2/$5 each, and the ready availability, there is a real incentive to use them instead of buying the more expensive genuine Lucas replacements.
Dan Masters

This thread was discussed between 04/07/2004 and 05/07/2004

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