[GoThingNC]

Originally Posted by Alan Herod

As a reliablility measure, I by-passed the fuse block located fuel pump fuse with an in-line bayonet style fuse. I also replaced the fuel pump relay and carry a spare. I think the correct fix is to replace the old fuse panels with new panels. The fuses and contacts themselves corrode and build up high resistance at the connection leading to sometimes dire consequences. Part of this could be in part because of off-gassing from a battery undercharge in a confined space with the fuse panel.

Alan,

Thanks for the info.

The fuel pump fuse looks like it was by=passed and the bayonet fuse had the meltdown and it ignited the plastic on the relays.

Here is the link to my friends SC that I mentioned earlier
Photos are on the second page of the thread.

http://forums.pelicanparts.com/showt...=377084&page=2

Within the last six months he:
Replaced the CDI box
New Bilsteins
New pads & rotors
Complete Rennaire A/C kit - Compressor, hoses, etc...
Strut-Bar
Rota 17 inch Fuch Replicas with new tires (only put 100 miles on them)
Leatherique treatment on the seats
Fuel Pump
Front Bumper smile strip
H-4 Head Lights
Door Seals
930 steering wheel
replaced the engine fan

[HoodPin]

Originally Posted by Alan Herod

.....I think the correct fix is to replace the old fuse panels with new panels. The fuses and contacts themselves corrode and build up high resistance at the connection leading to sometimes dire consequences. Part of this could be in part because of off-gassing from a battery undercharge in a confined space with the fuse panel.

FWIW, I don't think battery off-gassing is even required. My '71 Datsun 240Z surprised me with smoke from the console while driving it one day. Several of the fuse holders had gotten hot enough to melt the fuseblock, without blowing any of the fuses . And yes, the fuses were all the correct sizes.... It was a hot, smokey, glob until I disconnected the battery. Fuse block was nowhere near a battery. Ended up replacing the fuseblock with new. Discovered later that it was a common problem on early Z's. Attributed to the metal composition which gradually degraded over many years of conducting electricity. Resistance apparently increased to the point where heat became excessive despite current flow still insufficient to pop fuse.

If nothing else, this thread is a good reminder to check fuseblock condition on older cars. I think I've found another use for my infrared temp reader...

[GoThingNC]

Well I found out why the fuse was bypassed - the original holders were broken.

Per the Bentley a red wire is supposed to be connected from the top of the fuel pump fuse and joined to the top of the hazard/backup light fuse.

I finally finished splicing in the new fuel pump relay socket along with the window relay and new by-pass blade fuse (20 amp quick burn) and decided to start the car to see what would happen.

1st turn of the key and she fired up plus my dash brake light/seat belt light works

Now I can go about replacing the 10-fuse block and double checking the draw at the pump

Bentley manual states that the draw at the pump should only be 4 to 6 amps, but why is the fuse rated at 25 amp?

[HoodPin]

Originally Posted by GoThingNC

Bentley manual states that the draw at the pump should only be 4 to 6 amps, but why is the fuse rated at 25 amp?

Glad to hear you were able to solve the problem. I believe the 25 amp fuse may be required to deal with the fuel pump startup. AFAIK, most motors have an increased load at startup, and then level off to an operating level.

[GoThingNC]

Tony,

Thanks for the info.

I finished up replacing the 10-fuse block holder and it's now wired back to stock without the bypass fuse and the motor started up again

Now I just want to double check the amperage draw from the pump before I take a test drive.

[GoThingNC]

All is going well (knock on wood)and the pump is working fine, runs great, no heat build up at the fuses or relay.

Just out of curiosity, is it possible to check the current draw from the pump by hooking up a multi-meter in place of the fuel pump fuse holder so thay I don't have to jack up the car and check from underneath if I don't have to?

I'm just a little paranoid about the possibility of having another melt down.

Thanks !

[HoodPin]

I'm not an expert, and don't want to suggest anything that could damage your meter or pump. But it appears to be possible to measure at the fuseblock. The MM needs to be in series, not parallel, with the circuit in order to measure the current flow. Below is a link (I found via ask.com) that describes using the MM in place of the fuse.
http://p199.ezboard.com/fbasicelectr...picID=27.topic

I wonder if its possible to include the fuse in your circuit, just in case. Also, appears important that you set you MM on a high enough scale initially. I believe the easier method is to use a clamp type meter around the wire, but not everyone has one of the those....myself included.

[GoThingNC]

I
Tony,
Thanks for the link, it helped explain a lot
My neighbor has a MM with a high scale amperage rating with a built in fuse I can borrow.

I've seen on the market some of the clamp on MM, do they work by just clamping around the wire?

[smdubovsky]

Originally Posted by GoThingNC

I've seen on the market some of the clamp on MM, do they work by just clamping around the wire?

Yes, BBBUUUUTTTT most of those are AC only. There are AC/DC versions but they are more expensive. I use one here at work all the time (the DC version - I design battery chargers). VERY handy for currents above 10A where most multimeter fuses blow.

If you use/buy one, dont let the ends 'snap' shut. There is ferrite inside the C shaped part. Its a pressed magnetic ceramic powder thats brittle. Its easy to break it you expose it to shock loads. Then your readings go funny...

[HoodPin]

Originally Posted by GoThingNC

I
I've seen on the market some of the clamp on MM, do they work by just clamping around the wire?

Yes, they can sense the current flow and measure it. I believe its based on the same principle as the school experiment we all did by generating current by moving a magnet in & out of a coil of wire. I believe the meter is measuring the magnetic field generated by the current flow.