71 MSA fuse box question and blowing fuses

[timsz]

I keep blowing fuses for park/tail/amp. What is amp ? I see on old fuse box, ammeter amp. I did the voltmeter swap. I'll check wires again. Thank you.

[jfa.series1]

That would be a 20 amp fuse, same as OE. Blowing a fuse repeatedly says you have a dead short somewhere.

[SteveJ]

If the fuse is blowing, it's time to look closer at the circuit than to just keep plugging fuses into the fuse box.

Look at the wiring harness for splices.

Make sure there isn't anything poking up under the fuse box that could short the fuse.

Examine bulb sockets for corrosion and loose wires. (I had a loose wire on a socket that I found last December.)

Make sure you have the proper wattage/type bulbs if you're using incandescent bulbs.

[timsz]

The small white wire that powers the stop light is connected to the big white wire on pass. side. 1 side goes to voltmeter (swap) and other side goes to starter motor and alternator. Is that too much power ? Is that right ? What else does that small white wire power ? MSA fuse box.

[SteveJ]

 

1 hour ago, timsz said:

The small white wire that powers the stop light is connected to the big white wire on pass. side. 1 side goes to voltmeter (swap) and other side goes to starter motor and alternator. Is that too much power ? Is that right ? What else does that small white wire power ? MSA fuse box.

 

Irrelevant. That wire is before the fuse. What you're looking for is a problem between the fuse and the light bulbs.

[jfa.series1]

2 hours ago, timsz said:

The small white wire that powers the stop light is connected to the big white wire on pass. side. 1 side goes to voltmeter (swap) and other side goes to starter motor and alternator. Is that too much power ? Is that right ? What else does that small white wire power ? MSA fuse box.

We just went over the small white wire a couple of weeks ago - it goes to the horn and you posted that you found the matching female connector.  I just pulled my old fuse block - the wire coming off the fuse you indicated that is blowing is a small gauge green with white stripe.  Trace that wire to your likely short.  BTW - the stop light wire on the left side of the fuse block is a medium gauge green with yellow stripe but that's not the fuse problem you identified.

Edited July 10, 2018 by jfa.series1

[timsz]

I've been working on the electric for about 3 weeks. My brain is getting a blown fuse. Thank you.

[Phil Z]

I've been working on the electric for about 3 weeks. My brain is getting a blown fuse. Thank you.

When does the fuse blow? Stepping on the brake pedal? Just inserting the fuse in the holder? Turning the key to accessory? Turning the key to on? If I blows when you step on the brakes then disconnect the tail light assemblies and the park and side lights. Insert fuse. Step on brakes. If the fuse doesn’t blow then plug one item at a time back in and step on brakes. Did your old fuse block blow the same fuse and that is why you bought the new one? I looked at the pictures you provided earlier the first one shows the old fuse holder next to the new one. The old one shows two white wires with the same female connector both burnt somewhat. What does the writing on the wire tags say. Since both connections look identical and your new fuse block has two yellow connectors that look like splices, and in your latest picture you seem to have electrical tape wrapped around them. I am not familiar with the 71 wiring and long pigtails so I am guessing they go somewhere in the ammeter circuitry one possibly positive the other negative, but I am not sure. When you replaced the ammeter with voltage gauge did you observe the polarity? Are the two white wires observing the possible polarity? Someone jump in here that knows more than me! When does the fuse blow?


Phil Smith

[Phil Z]

When does the fuse blow? Stepping on the brake pedal? Just inserting the fuse in the holder? Turning the key to accessory? Turning the key to on? If I blows when you step on the brakes then disconnect the tail light assemblies and the park and side lights. Insert fuse. Step on brakes. If the fuse doesn’t blow then plug one item at a time back in and step on brakes. Did your old fuse block blow the same fuse and that is why you bought the new one? I looked at the pictures you provided earlier the first one shows the old fuse holder next to the new one. The old one shows two white wires with the same female connector both burnt somewhat. What does the writing on the wire tags say. Since both connections look identical and your new fuse block has two yellow connectors that look like splices, and in your latest picture you seem to have electrical tape wrapped around them. I am not familiar with the 71 wiring and long pigtails so I am guessing they go somewhere in the ammeter circuitry one possibly positive the other negative, but I am not sure. When you replaced the ammeter with voltage gauge did you observe the polarity? Are the two white wires observing the possible polarity? Someone jump in here that knows more than me! When does the fuse blow?


Phil Smith

Also, for curiosity’s sake, take apart your MSA fuse holder and inspect it for shorts to ground. Don’t mount the fuse holder to the car to see if that stops the fuse blowing. Good luck. Don’t be con•fused •


Phil Smith

[jfa.series1]

10 hours ago, Phil Z said:

When does the fuse blow? Stepping on the brake pedal? Just inserting the fuse in the holder? Turning the key to accessory? Turning the key to on? If I blows when you step on the brakes then disconnect the tail light assemblies and the park and side lights. Insert fuse. Step on brakes. If the fuse doesn’t blow then plug one item at a time back in and step on brakes. Did your old fuse block blow the same fuse and that is why you bought the new one? I looked at the pictures you provided earlier the first one shows the old fuse holder next to the new one. The old one shows two white wires with the same female connector both burnt somewhat. What does the writing on the wire tags say. Since both connections look identical and your new fuse block has two yellow connectors that look like splices, and in your latest picture you seem to have electrical tape wrapped around them. I am not familiar with the 71 wiring and long pigtails so I am guessing they go somewhere in the ammeter circuitry one possibly positive the other negative, but I am not sure. When you replaced the ammeter with voltage gauge did you observe the polarity? Are the two white wires observing the possible polarity? Someone jump in here that knows more than me! When does the fuse blow?


Phil Smith

Phil - The pic you referenced was mine, not Tim's.  The female spade connectors were not burnt, merely had aged covers and as best I recall I had them labeled as Main A and Main B as were the male sides of the harness before I disconnected them.  The MSA unit has butt connectors in place of spades, probably for the simple reason of the difficulty of getting the correct size female connector.  With the MSA unit, you have the choice of cutting off the large male spade connectors and hard wiring the matching dash harness into the fuse block wiring or moving the old female connectors to the new fuse block - the option I took after this pic was made.

Here's a pic of the backside of my OE fuse block (actually in excellent condition).  You can see that both large gauge white wires go to the same place, how they are connected to the dash harness becomes irrelevant.

[Phil Z]

Thanks for showing me the back side and I would agree that those two white wires are actually sharing the power as the 72 Z had a single larger wire. We wait for a reply from timsz. Thanks again.


Phil Smith

[timsz]

I'm working on the grounds. I found a 4 pin connector behind the gauges. It has the small pins. It has a lw wire that goes to rheostat, bulbs, radio. 2 other wires that I can't remember what they are. It has a black wire on 1 side of the connector ( going to ground, I checked ) the mate on the other connector is a 1 inch white wire, apparently cut. I have no idea how it got like that.