914 Fuel Pump fuse on relay board blows Options

[Sea Dragon 914]

Does anyone know what are common causes of blowing the fuse on the engine relay board for the fuel pump and how to diagnose it? Would a bad fuel pump cause this?

Thanks,

[Dave_Darling]

The most common cause is that the aux air regulator wire is shorting to ground. Either where the wire goes into the bottom of the "can", or the wire is unplugged and touching ground that way.

--DD

[Sea Dragon 914]

Thanks Dave. I'll check it out this morning.

SDR

The most common cause is that the aux air regulator wire is shorting to ground. Either where the wire goes into the bottom of the "can", or the wire is unplugged and touching ground that way.

--DD

[Sea Dragon 914]

Kind of worked. I disconnected the Aux Air valve connector and electrical taped the ends. Car fired right up. Drove about a mile and a half and the fuse blew again. Do you have any other suggestions of where to look?

Thanks,
SDR

The most common cause is that the aux air regulator wire is shorting to ground. Either where the wire goes into the bottom of the "can", or the wire is unplugged and touching ground that way.

--DD

[Mike Bellis]

Looks like the heater fan may come from that circuit.

[Sea Dragon 914]

If I'm reading the schematic correctly, there should be a 25 amp fuse. Is that correct? Mine had a 16 amp.

SDR

Looks like the heater fan may come from that circuit.

[Mike Bellis]

If I'm reading the schematic correctly, there should be a 25 amp fuse. Is that correct? Mine had a 16 amp.

SDR

Yes

[euro911]

The low-rating fuse is the probable cause, but check the path for corroded connections as well. Corrosion on terminals will cause a higher current draw in a circuit.

[Dr Evil]

But, also consider that the heater fan (decent amp draw) and AAR do share that current path. So, place in proper rated fuse, check all wires at those two pieces, and relax (IMG:style_emoticons/default/smoke.gif)

[9won4]

Thank you...thank you!! Just ran into this problem yesterday and was about to have the car towed. It was that little little wire not protected underneath the auxiliary air valve. Love this forum...you guys are the best!

[Tom]

SDR,
A lot of folks started using a 16 amp fuse in that spot. Unless you have the rear window defrost, a 16 amp is adequate. That fuse protects ( used loosely ), the following; fuel pump - about 5 amps, heater fan - about 5 amps, rear window defroster Don't know the amps for this. and last the AAR - about 1 amp. So if you are not using or don't have a rear window defroster, your normal draw max would be about 11 amps. No reason a 16 amp would not be enough. If you have been running a 16 amp for some time and have no rear window defroster, you have something else going on. Putting a larger fuse in could lead to overheated wires on the circuit that is causing increased current flow.
The wires for the AAR are sized for about 10 amps max continuous. If the wire to the AAR starts to short to ground and causes increased current flow, this has happened to several members here, it can cause a fire in the ignition harness. With a 16 amp fuse being used and the fuel pump running, there is a better chance that the fuse will blow before a fire starts. Every member that had a fire caused by the AAR was using a 25 amp fuse. Had they been using a 16 amp, the outcome might have been different. The other thing that you can do is run a 25 amp but install a 5 amp in-line fuse where the AAR plugs into the harness wiring.
Tom

[euro911]

A bad ground will tend to cause an increase in current draw as well. Make sure all your grounding points are clean and have tight connections.

[screenguy914]

The low-rating fuse is the probable cause, but check the path for corroded connections as well. Corrosion on terminals will cause a higher current draw in a circuit.

To be most correct, if voltage is constant, additional circuit resistance decreases, not increases current flow. Same with faulty ground connections.

Except for a partial or complete short to ground (via circuit path or a malfunction in the load itself, bulb, motor, heating element, etc.), circuit current is a result of the total current requirements of the load(s) in the circuit and how the circuit path is wired.

However, if a circuit connection point, e.g. splice, connector, etc. has excessive resistance due to corrosion or bad contact, that will 1. reduce voltage and thus current available to operate the load and 2. Create resistance and thus heat at that location. If the loads normally have high current needs (e.g. motors, heating elements, etc.), heat will be created at the point of excessive resistance.

I suggest isolating the branch circuit(s) by disconnecting the source wires for each of the loads until the offending load is identified.

Oops. Looks like you found the source of the excessive current draw. Congrats on your diagnosis and discovery and suggestions from others.

Sherwood

[velum]

Looks like the heater fan may come from that circuit.

Thanks for the diagrams! I had the same problem and studying them helped me to understand what was connected to the same fuse as the fuel pump. I removed the auxiliary air regulator to measure its resistance, but it was ok, so I also unplugged the rear defogger relay, and my fuel pump is now working. I could not tell though whether removing the rear defogger relay or unplugging and replugging the AAR solved the issue, but it is probably the former one.

[Alaska914]

Where is the aux air regulator wire located. I’m having the same issue keep blowing fuses. Also I noticed in my Manuel it calls for a 30 amp fuse is this correct? Thanks in advance