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1969 Giulia GT Junior, with 2 litre conversion
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Discussion Starter #1
Hi. I have a 1969 GT Junior, which now blows fuse #6 when ever the ignition switch is turned on.

In my car there is only a single pink wire coming from the cold side of the fuse, which feeds the dash gauges. I've not made any changes to the car recently, other than late in 2019 I fitted some LED BA9S bulbs in the water temp and fuel gauges and also the speedometer, which when tested were a significant improvement on the standard bulbs (these are on a seperate fuse in the fuse box). At the time, the fuse #6 was intact and did not blow.

I came to start the car about a week ago, and went to crank the car over with the plugs removed to ensure there was oil pressure prior to the first start. The (veglia) oil pressure gauge in the side of the tacho didn't move and the low oil pressure warning light also didn't light. The fuel gauge also didn't move. I checked fuse 6, which had blown. I swapped out another known good fuse, which instantly blew when I turned the key suggesting a short to ground.

I've now tried the following:

1) with all 4 dash connectors (oil pressure gauge, warning lights in speedo, water temp and fuel level) disconnected, there is no connectivity between the cold side of fuse 6 and ground (I'm using the steering column as a ground reference point).

2) with the fuel level gauge connected, and again placing the multimeter between the cold side of fuse 6 and ground there is no beep on the continuity tester, but a resistance of around 75 ohms, which is commensurate with half a tank of fuel. The fact that resistance is greater than zero is good as this suggests no short to ground.

3) when gradually connecting the other 4 connector blocks, the resistance falls to around 5 ohms total. This is confusing me, as I thought resistance was additive?

4) I've tested the individual feeds into the back of the connector blocks for the oil pressure warning light, the oil pressure sender, water temp sender and found that in isolation, all of these have a resistance of 0.6 ohms along the cable (i.e. these are not broken) and when removed from their various senders are not shorting to ground anywhere.

Short (if you pardon the pun) of just throwing fuses at the situation, I'm running out of ideas.

To confirm, my dash lights are on another circuit. My reverse lights are on another circuit. All my vehicle lights are on alternative circuits.

Any suggestions as to what to try next?
 

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This is confusing me, as I thought resistance was additive?
Resistance in series is additive. Resistance in parallel is lower than the lowest resistor. The formula is simple for two resistors and becomes more complex for more resistors.
I would put the loads back in one at a time until the fuse blows and the last one connected is most likely the problem.
 

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I had a similar problem after replacing the dash lights with LED's on my Spider. What I eventually (and I do mean EVENTUALLY) found was the wires on the back of the tach or speedo (can't remember which) were bent at a 90 degree angle when installed and touching the metal housing. The angle was such that the end of the wire was exposed (but only when bent), and when power was applied, the fuse would blow. I would retrace your steps with the bulb install and check all of the wires. Maybe pull the speedo and tach out and turn the key on and see if the fuse holds.

Chuck
 

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1969 Giulia GT Junior, with 2 litre conversion
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19 Posts
Discussion Starter #4
Thanks guys. Sounds like a logical way forward. I will pull the dash out at the same time to see what else I can tidy up wiring wise. It also provides a clear view of what's happening when I re-connect each of the instruments to the main dash harness.

Chuck - I don't suppose you can recall which wires were touching the back of the speedo/tacho? I will also pull all of the LEDs out of each instrument to check if there is any wierd grounding issue going on.
 

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If I had to guess I would say it was the generator warning light wires. That connector stick out further than the normal lights.
 

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1969 Giulia GT Junior, with 2 litre conversion
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19 Posts
Discussion Starter #6
Solved! As expected, it was something simple. The crescent shaped bracket which is used to fix both the fuel and water temp gauges wasn't fully located on both pins on the water gauge which give the opportunity for a short. Hard to spot at a glance!
 

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1969 GTV 1750 Australia
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316 Posts
Good pick up. I have to do the gymnastics to climb under the dash to trace some dead bulbs and missing connections. Has been on the top do’ list for a while, but low on priority and enthusiasm.
 
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