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Fuel gauge Elec. gremlins

M

Mike snyder

Donation Time
Hi all,
I am having some problems with my fuel gauge.

Background:
1. 1964 SIV GT sat for a long time.
2. Converted car from pos. ground to neg. ground
3. Original voltage regulator was shorted out between poles labeled "I" and "E" (got a continuity read). Got solid state voltage regulator from SS for neg. grounded elect. system.
4. checked wire to sender unit got continuity so that is good.
5. Added some fuel to tank got no change in Ohms reading....
6. Took apart tanks cleaned tanks and sending unit and got perfect Ohms read (can't remember the exact specs.)
7. Hooked everything up and fuel gauge worked.
8. Car sat for three months due to work schedule. Started car no fuel read...
9. looked under dash. Mounting screw for voltage regulator was lose and arced when I touched it...
10 Assumed I shorted it out bought new one hooked it up no read on Gauge...
11 Rechecked Ohms. on sender unit ( bounced car with half tank of gas and got change in Ohms.)
12. Bought 2ed. voltage regulator...
13. hooked it up. had it hanging under dash with alligator clip to make ground... accidentally bumped clip off and got smoke from voltage regulator!

Questions:
1. Have I fried another voltage regulator?
2. How do I check? (OHM reading or other??)
3. Did I attach the wires wrong? There are lugs on the original labeled "I" and "B". I just switched wires from one to the other.
4. How do I check if the fuel gauge has died?

Thanks in advance,
Mike
 
Cactusmasher

Cactusmasher

Donation Time
Electrical gremlins-gauges

Mike: The following is verbatim from the Rootes factory shop manual.....

"Instrument voltage stabilizer Servicing Precautions....

1. Ensure that the cables from the instruments are connected to their proper terminals on the stabilizer.

2. Ensure that the stabilizer is mounted with its securing lug set vertically and the fixing hole downwards.

3. Ensure that the stabilizer is effectively earthed through its mounting lug."

You can insert "regulator" for stabilizer and "mounting tab" for mounting lug.
"Earthed" means grounded.

The letters stamped into the stabilizer next to the wire mounting prongs mean as follows: B goes to A4 on the fuse unit......E goes to ground.....
I connects to the rear prong on the left side of both the fuel gauge and the temp gauge ( looking at the rear side of each gauge as mounted in the dash)

The sending unit wire from the gas tank and the temp sending unit are both connected to the right prong on each individual gauge, again looking at the rear of the gauge as mounted in the dash.

"The mean voltage between terminal "I" and earth (ground) is 10 volts. Renew the stabilizer if faulty" The only 12 volt reading should be incoming electricity to terminal "B" on the stabilizer.

You will have two wires coming off the I terminals, one each going to the fuel gauge and one to the temp gauge when correctly hooked up.

If you still have original Lucas wiring, connections tend to corrode over the years. Bad connections and bad grounds are the usual suspects in faulty gauge operation. Also look at the prong or spade on top of the fuel sender on the gas tank. They also get corroded and/or covered with oil, grease, rust or whatever. Both gauges are relatively simple in their operation and it's not likely the gauges are the problem. I hope this information is of some value in correcting your problem.:)
 
G

greenbean

Donation Time
I hope it is not the problem that I had. I pretty much did everything that you did and found out I had a crack in my float and it was full of fuel :mad:. replaced the float and I have a full range of measurement ;).
 
T

Tom H

Platinum Level Sponsor
Mike,

You mention Ohms readings, so I assume you have a multimeter, that can measure Volts as well as Ohms. I don't understand why you have made so many swaps of the voltage stabilizer without measuring any voltages.

By the way, I suspect your original stabilizer is still OK. You say you measured "continuity" between the E and I terminals. The regulating coil is between those terminals and I think it is about 120 Ohms, so just about any ohms function would show this as "continuity" and depending on how low a range you have on your meter it might actually read the accurate number of ohms. You should also see "continuity", but less than 1 or 2 ohms at most, between terminals I and B. Those terminals are contacts that open only momentarily, about 2 times per second when full battery voltage is applied.

Easy to check if any of your voltage regulators are fried. Hook it up. Make sure the case is grounded, OK to use an alligator clip lead to ground it. Connect the 12 V supply (green wire) to terminal B. Do not connect anything to terminal I, Measure the voltage at Term B. (other lead on meter connected to chassis ground, of course). With the key On you should measure about 12.6 V (battery voltage). if no 12 V find why . Maybe you have connected the gauge wire instead of the 12 V supply wire. (not sure what color the wires to the gauges are on an SIV) .

Assuming you have 12 V at term B. measure at Term I. It should be 10 V. If it's the same as the V on Term B, double check that you have a good ground to the case (term E). If it's still same as Term B , it's fried, but the gauges should still work, just they'll read high. If the voltage at Term I is zero, again, it's fried , but the gauges will not read at all.

Next step, assuming you can get one of your regulators to work at least well enough to have 12 V at term I, connect the fuel gauge wire to term I and connect the sender wire to the Fuel gauge. Measure the voltage at both terminals of the Fuel Gauge. One terminal should read same as out put on Term I of the regulator. The other terminal should read lower voltage. If both terminals read the same, the circuit to the fuel sender or the sender itself is open. If one gauge terminal reads lower voltage, as it should, the gauge should show something other than it looks like when the ign switch is OFF.

Let me know what you find. And note that you can always test the senders and gauges by swapping wires. The gauges are identical except for the marks on the dials . A quick test of the gauges is to wire connect 12V to one terminal on one of the gauges, connect the other terminal to one of the terminals on the other gauge, and then connect the other terminal of the second gauge to ground. both gauges should read about the same and a little over half scale.

Tom
 
M

Mike snyder

Donation Time
Update on the fuel gauge/ temp gauge problem.

Works been crazy so it has taken a long time to post. This is what happened. Some how the temp. Gauge failed internally and produced a short that was causing the step down regulator to over heat and fail. After replacing the step down regulator and leaving off the power to the temp. gauge the fuel gauge worked. When I plugged it back in the fuel gauge stopped working and the temperature of the step down began going up. I took the car to a local British car garage for some additional work and they also verified the problem So I am going to send off the gauge to be rebuilt along with the speedometer which can,t seem to decide if i'm doing 50 or 90.
Thanks,
Mike
 
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