typical fuel gauge/instrument cluster question
is it safe to assume that there wouldn't be much harm in installing a solid state regulator without disassembling the fuel gauge to remove the old mechanical?
Only if it's completely dead, which is often not the case. If the needle still moves at all, it must be getting an input voltage from somewhere... and at 40+ years old, that input is usually not reliable, which is why you asked the question in the first place.
First, some theory. The old mechanical "regulator" is essentially a buzzer. It oscillates between supplying 0V and 12V, which averages out to about 5V or so. Because the gauge needles are bi-metal thermal units, they move slowly enough to damp out the vibrating input supply. (A switching signal is not really "old school" except in how it's created... nowadays, we see these kinds of signals created electronically, varying the duty cycle (the on/off ratio) to create pulse width modulation controls, etc.)
Adding a new electronic regulator is a fabulous idea, and results in renewed gauge reliability for probably another lifetime worth of driving. Here's a pictorial article that Daryl wrote about his 64 Valiant...
http://earlycuda.org/tech/gauge-convert.htm
Note that this type of surgery is complicated only on the older style, when the regulator is actually internal to the gauge. The newer style regulator is a separate little external metal canister that plugs into the back of the circuit board-- it's comparatively quite easy to perform surgery on that one.
Here is a list of internal/external voltage regulator applications.
Those mechanical buzzer units have amazing longevity, but eventually any of them will die-- or partially die, or change behavior based on different temperatures or phase of the moon or what you ate for breakfast... which is the reason I wouldn't recommend trying to run two regulators in parallel. If you're going to go to the trouble of incorporating a reliable regulator to give you years of driving pleasure, it's certainly not a lot of extra work to disconnect the old one. The gauge will be much more predictable when it has only one (rock solid) source voltage.
- Erik
64 Valiant, 170 3-spd
82 Volvo wagon, 5.0 5-spd :)
