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7 Volt Regulator Problems

A "step-down" auxiliary voltage regulator drives the fuel and temperature gauges on GL1000s. This clever device provides a constant 7V input voltage to power these gauges. This effectively buffers the wide normal fluctuations in battery voltage. Without the step-down regulator, your gauge readings would be very unreliable because main battery voltage varies with rpm, load, stator output and accuracy of the voltage regulator. Many older cars use this same technology for the dashboard. As a side note, I find the coolant temperature gauge to be reliable and accurate. The fuel gauge is neither! This is mainly the fault of the fuel gauge sending unit within the fuel tank.

On the earliest GL1000s, the step-down regulator mounts on the left side of the top shelter - below and to the right of the fuse box (it actually passes through an opening in the shelter side and is held in place by a plastic clip).

7 Volt Auxiliary Regulator

A "Full" fuel tank or pegged "Hot" coolant reading is indicated by the respective gauge when it "sees" a full 7V. Lower readings are achieved through the variable resistance providing by the sending units for each gauge.

Problems with this device are revealed whenever both gauges (fuel and coolant temperature) simultaneously act flaky. There are 2 failure modes:

Chronic Low Gauge Reading - both fuel and temp read "low" contrary to actual values

Not explained by bad fuse or wiring fault. 7V regulator has failed in the open mode...passing no juice at to the gauges. You end up with false "Empty" and false "Cold" readings at the same time.

Chronic High Gauge Reading - both fuel and temp read "high" contrary to actual values

7V regulator is continuously or intermittently passing more than 7V input to the gauges. You end up with false "Full" and false "Hot" readings at the same time. Be aware that this condition will quickly fry your very expensive gauges not to mention creating a serious fire hazard.

Testing

Failure is usually obvious based on the two chronic conditions described above. However, there is a simple output test described in Section 17, page 13 of the official Honda Shop Manual if you're interested.

Solutions

• New OEM part - Honda part # 31410-371-007 (pricey...current $80+ list price from Honda!)
• Salvage part (OK strategy as long as you get return privilege)
• Reproduction 7 Volt regulators show up on EBAY from time to time
• Make you own 7 Volt regulator from bits sourced from electronic supply store such as Radio Shack. Here's a link to plans courtesy of Bob Kekeis:

  7Volt Regulator plans

• Gary Dordevic of Houston, TX created and tested this version on his '78 GL1000:

• John Meriweather of Arkansas recently sent this good idea:

  "I read your Tech Tip on the 7 volt regulator for the fuel and temp guages. The link to the diagram for building one from Radio Shack parts was good; however, there are some of us who are not electronicaly inclined. I did find a more readily available substitute behind the dash of a junk Ford (late '70's...early 80's vintage) There is a voltage regulator for the car's fuel and temp guages. What is so unique about this part is that there is an adjusting screw for increasing the voltage output from 6>7 volts. It's almost a plug-and-go operation. The Ford dash regulator has connection points like a 9V battery. Any junk radio with these conectors will do. Simply split in half and press on the appropriate terminal then connect to the wiring harness. It is also marked IGN on the terminal. Mine is working like new again for the cost of less than $1.00 I hope this helps others as well. The donor car was a 79 ford LTD. I have also found this part on a '66 mustang, 79 XL and Mercury Comet."

Caution: Don't ignore problems with the 7V regulator. As mentioned above, a faulty 7V regulator can quickly fry both fuel and temp gauge which is an expensive problem to solve.

Note: If only one of the two gauges (fuel and coolant temp) is acting up, the problem is not with the 7 volt regulator.

See also: Tech Tip: Fuel Sender Issues

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