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In a recent thread, a known hijacker asked about a fuel pressure gauge I mentioned installing on my truck. I won't mention the hijacker's name, because I don't want to embarrass 'WhatsAChevy'. Not wanting to fully hijack that discussion, I'm posting details here instead.
On my '84 F250 (351W 2bbl), I've added a Holley 26-503 fuel pressure gauge:
The sending unit is located on a tee fitting added at the carb inlet. Adding this tee moved the fuel filter about an inch closer to the radiator, so it was necessary to shorten the metal fuel line and reflare the end.
Clearance was very tight to install the sending unit. The adjacent coil doesn't leave a lot of room. It was necessary to angle the sending unit up slightly to clear the coil. The sending unit is about 2" diameter and 1.5" tall, plus another .5" for the wire terminal stud on the top. It has the same 1/8" MPT threads as the fuel filter.
Note the heat shield around the front of the carb and the cooling air line feeding air diverted from the AC plenum. The cooling air line is a steel tube inside a braided heat shield.
If you are eagle-eyed, you'll also notice the coil in this picture is not connected to anything. This is the stock location, but I recently installed a new coil on the back of the bracket for the AC compressor. The old coil was left in place as a hot spare if the new one should ever fail:
If I were to ever redo the whole thing, I'd probably remove the coil from the stock location. This would have give me a lot more room to install the fuel pressure sending unit. But since the coil is already there and it does clear the sending unit (if barely), it's staying.
Here's the view of the gauge, installed in a bracket under the lip of the dash:
The gauge works very well. It reads downstream of the fuel filter, so it shows exactly what is going on at the carb inlet.
Actually, I'm going to stick to your original question. This is a family-friendly forum, so let's stick to talking about trucks.
It's a momentary-on switch to run the electric fuel pump. I removed the stock mechanical pump and installed a blocking plate. I only have an electric pump (Carter P4600HP) now, installed just forward of the tank selector valve.
The circuit goes through an oil pressure safety switch, to shut off the pump in the event of a loss of oil pressure. This isn't so much to protect the engine, but to protect me and any passengers. If a fuel line were to break (in a crash or otherwise), the electric pump would not know and would keep running and potentially feed a fire. Adding the oil pressure safety switch mimics the general safety standard of a mechanical pump, i.e. if the engine is turning, it is already receiving fuel, which hopefully means the fuel lines are intact so it should be safe to continue feeding it fuel. If the engine stops turning for any reason, the pump also stops. You can't use an ordinary on/off toggle switch and assume you'll be able to manually shut it off in an accident. The risk of creating a Car-B-Q is just too great to not have an auto shutoff feature.
The switch has a pilot light, which I've wired to show when power is reaching the pump. This is optional, more of a gee whiz thing.
I use the switch's momentary on feature to bypass the oil pressure safety switch to refill the carb if the truck has been sitting for a few days and fuel has evaporated from the carb. You don't have to crank and crank and crank like with a mechanical pump. The engine starts instantly, no matter how long it has been sitting. In addition, if the oil pressure safety switch were to fail open, I could limp home by holding the switch to the override position.
After being stranded twice due to heat apparently affecting the fuel system, it was time for drastic measures. I think the issue was caused by too much heat reaching the carb, and was not a traditional vapor lock problem in the lines reducing fuel flow to the carb.
When I ditched the mechanical fuel pump and went electric, I also added the gauge to monitor fuel pressure just in case I had been having a problem getting fuel to the carb.
So far fuel pressure from the electric pump has been spot on at 6-8 psi. I've had zero fuel issues since converting to the electric pump and keeping the carb cool as described in the link above.
I just wish I had the gauge back when the truck acted up, so I could be positive what was causing the trouble at the time.
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