Hot ignition switch solved, melted insulation

[YIIHAA]

I know this is a subject to be filed under "old chestnut", but I fitted a relay after fuse 1 (15 amp) today (following Steve D's guidance from another thread).

This has reduced the peak current through the ignition switch from about 10A, down to the 12mA to power the relay. My dash voltmeter now reads battery voltage even with the blower running at full power, as opposed to before when it read up to 1.7V lower depending on the current draw. Now my ignition switch doesn't even get warm.

Before I fitted the new relay I did some checks and was getting a voltage drop of about 1 volt just across the switch. What was more worrying was the insulating sleeve on the connector of the white wire had melted (the one that feeds fuse 1 and most of the cockpit electricals). This can't be good.


Don't know if the factory have changed the design since I built mine (2001), or if I have a defective switch.

[davefiddes]

How many white wires do(did) you have going to your ignition switch? I have two wires going to both terminals and I've not noticed the ignition switch getting warm or the voltage reading dropping. Mine is a June 2002 loom. Looking at your picture it could be that it was the contact<->wire interface that was heating up rather than the switch contact itself???

[GTRMikie]

My car suffered exactly the same symptoms as YIHAA. After one run with "everything on" I actually burnt my thumb and forefinger when I turned off the ignition! The key and ignition switch were extremely hot with molten terminal insulator as in the picture. However the insulation on the wires was undamaged. I assumed the problem was a very bad, high resistance contact between the spade terminal on the cable and the switch or a faulty switch. I ensured a good contact and replaced the ignition switch. Since then I have had no trouble, but I find myself feeling the ignition key every few miles just to make sure! My loom is also an early one (1998) and the relay sounds like a good idea!

[YIIHAA]

davefiddes said:

How many white wires do(did) you have going to your ignition switch?

Two wires each in two connectors, like yours. One of the connectors (the melted one) seems to provide all the power to the cockpit(blower fan, instruments) and fuel pumps. The other I presume feeds the coil (after reading all of the wiring notes).

The problem isn't the spade connection with the switch, as I measured voltage drop across the switch terminals. So it's just a crappy switch, that probably isn't designed to carry that much load.

Or maybe it's just MY switch (along with about 10 other people on here)

[davefiddes]

YIIHAA said:

Or maybe it's just MY switch (along with about 10 other people on here)

I think I saw on somebody's price list that it was rated at 25A. Sounds like this is more an aspiration than anything...

You can bet that the inductive surge from fuel pumps and the like will be a lot more (and cause arcing).

A big relay is a lot cheaper than a new ignition switch...even a cheap and nasty one.

[ultimasimon]

davefiddes said:

YIIHAA said: Or maybe it's just MY switch (along with about 10 other people on here) I think I saw on somebody's price list that it was rated at 25A. Sounds like this is more an aspiration than anything... You can bet that the inductive surge from fuel pumps and the like will be a lot more (and cause arcing). A big relay is a lot cheaper than a new ignition switch...even a cheap and nasty one.

..and the fuel pumps are fed directly from there as well?? No wonder why my volt guage bombs out when I flick the AC on. I thought the pumps would be on a relay? Going to consult the build manual.

[YIIHAA]

Item 42, Fuel tank change over switch:
Common on one pole of the switch is the white positive supply from the ignition switch. (fed from the second pair of white wires on the switch, that feed the coil/fuel pumps, so not affected by my fuse 1 modification)

Common on the other pole of the switch is the sender feed.

Output of the switch is to white/purple or white/green, which supply the fuel pumps via independant 10amp fuses (3 and 4 when looking left to right from the front)

>> Edited by YIIHAA on Thursday 8th July 17:46

[ultimasimon]

YIIHAA said:

Item 42, Fuel tank change over switch: Common on one pole of the switch is the white positive supply from the ignition switch. (fed from the second pair of white wires on the switch, that feed the coil/fuel pumps, so not affected by my fuse 1 modification) Common on the other pole of the switch is the sender feed. Output of the switch is to white/purple or white/green, which supply the fuel pumps via independant 10amp fuses (3 and 4 when looking left to right from the front)

Thanks Paul. That should be easy to modify then. I have modified my fueling setup to allow for the extra demand when used with the nitrous. I joined both my two #6 fuel lines at the bottom, then fed them into a Mallory 140 gph race pump, which draws twice the current that the standard one did. The pump on the other side is used to provide the extra fuel when the nitrous is 'having it' so I can bung this on its own supply at the same time.

As my tank changeover switch does nothing other than read tank levels, I can pick up the relay feed from that point and then just run a bigger auxillery feed. I am going to run all the circuits through my AVO and measure all the current readings in all different situations.

I also want to add a power relay for the fan I put on the oil cooler, which has not yet been connected. I will set this to run only when switched manually with the cooling fans. I am also toying with fitting a rear canopy fan, to agitate the air when stationery.

If anyone else has any advice on other electrical 'mods' that have caught their attention while in the build, please let me know, as they could be done at the same time.