electrical challenge !

[shithotfast]

Notice that when I tun on the ign the dashboard voltmeter shows 12 volts - ok. If i switch on some lights and heater fan, volts drop to around 8 volts. I thought the battery was duff, but if I check the voltage at the battery terminals it show 12.5 volts at all times, but the volt meter is showing 12 down to 8 or less. When I crank the engine volts drop off the scale on the dashboard, but stays high at the battery terminals? Engine cranks very slowly.

Some kind of earth problem I guess. Anyone had this? Ideas? Also... when driving, charging voltage shows 14 volts at all times even when (new) battery is fully charged.

[Steve_D]

The volt meter should be connected to a very heavy wire so there is no voltage drop and ideally direct to the battery but this would leave the gauge on all the time and run the battery down. It must also have a heavy earth.

If you don't already have one, an ignition load relay would be the ideal way to wire the gauge with heavy lead from the battery through the relay and then to the gauge and anything else the ignition switches. Turning on the ignition would then only operate the relay. This is worthy of note to any owners who suffer the 'Hot ignition switch' syndrome.

If this is all related with a slow cranking then the earth fault is between the chassis and the battery.

Steve

[San Diego GTR]

I had this problem too when I first started testing the wiring. My battery had sat for nearly a year without a charger on it and it simply needed a good long charge. Does the voltage read the same at both the battery and the voltage gauge in the cab?
Paul

[shithotfast]

San Diego GTR said:

I had this problem too when I first started testing the wiring. My battery had sat for nearly a year without a charger on it and it simply needed a good long charge. Does the voltage read the same at both the battery and the voltage gauge in the cab?
Paul

The battery is good 12.4 volts even under load - lights/fans - but the voltage gauge says 8 ish volts. I am going to re check every earth wire.

[SimonMaidenhead]

When this happened to mine, I found that the earth wire between the alternator and chassis was loose at the chassis end. I also took a bit of emery cloth to the powder coating, just to ensure a good earth.
Worth a look?

[Silverspyder]

Had a similar prob on my spyder a year or so ago - eventually traced the problem to the main earth leads to the chassis. Removed them all and cleaned both the terminals and the surface contact points on the chassis.
Not only cured the problem but made a huge difference to engine start cranking speed, which had always been slower than I thought it should.
Hope you get it sorted.....

[SplatSpeed]

hi paul do you want me to come round and have a look

there is a voltage drop somewhere due to resistance

the voltmeter should be running very low currant

something in the voltmeter line is using a lot of currant and therefore not reading correctly

should take a couple of mins to find and my daily commute is past your place now

Sean

[shithotfast]

SplatSpeed said:

hi paul do you want me to come round and have a look

there is a voltage drop somewhere due to resistance

the voltmeter should be running very low currant

something in the voltmeter line is using a lot of currant and therefore not reading correctly

should take a couple of mins to find and my daily commute is past your place now

Sean

Sean, That would be great. The problems are getting even stranger now.... Headlights looked a bit dim, measured the voltage at the lamps - 6 volts?! Battery says 12.5 volts. Side lights are fine... rear lights are fine.....

I have replaced the floor dip switch - no change, and the dashboard on/off light switch - no change.. cleaned all earth wires /straps - no change..... I have lost my wiring diagram if anyone has one (link on FAQ doesn't work) Could it be the relays ? I need an electrification expert!! !! I will send you my mobile number - perhaps we could have a chat....

Edited by sthotfast on Wednesday 18th June 20:20