fuel gauge giving weird reading after installing spotties

[j-top paj]

i installed an extra set of spotties to the fron of the trol a couple months ago and everytime i turn the spotties on now the fuel gauge drops.
when i first installed them i had a completely full tank and i went for a drive to test them out and the fuel gauge droped to 3/4 as soon as turned them on. it seems to drop it by anywhere between 1/4 and 1/2 of the original reading.
i cant work out why its doing it
i took the triger for the relay of one of the original spotties.
it only does it to the main tank not the sub.

anyone got any ideas?

[Mr.Smith]

very interesting
i c in ur signature u have a GU, i recently purchased an 89 TD42 gq wagon and have experienced the same problem. tell us some more details how many spotties in total, how many relays u have ect

i've got 4 spotties on the front 1 relay per pair so 2 X relays sharing 1 common trigger and earthed at the same point.

if ne 1 can help or shed some light on y this happnes please do

[j-top paj]

the original pair of spotties were already wired up when i got the car and im asuming that they are trigered of the high beam.
they have a relay and a switch in the dash.
when i coneceted an extra pair i took the trigger of the positive of one of the spotties and conected it to the new relay. so the first pair actually trigger the second pair. i dont see any probs in this but something is making the fuel gauge go weird

how did you wire up yours?

[Mr.Smith]

basicly the same way as what u have
i will have to talk to some of the guys at my work and c if they know what the go is.

[j-top paj]

let me know how u go, its starting to annoy me a little.. i was hoping it would "go away" by now

[MART]

Check for voltage drop over your main power bus , also how are you feeding the lights , hopefully not from the the original source , as you might be overloading the system. Need to run a feed from battery directly via a fuse to be switched through relays to turn spotties on. The original feed should only switch relay off and on. As people upgrade there
original lights from say to 90,100,130 watts the cabling can't handle the extra load , therefore the fillaments don't get hot enough and become brittle and break due to vibration. Maybe you are taking to much power for your lights and this is affecting your fuel/sender system , might help , Cheers Paul.

[ausoops]

bad earths.

the lights are earthing through the tank sender. try running a new earth to the bullbar straight from the battery neg - or from the body not the chassis. and/or earth the chassis to the body with a earth strap.

[j-top paj]

thanks, il try the earth. but from memory i think i took the earth from the body of the car or directly off the battery... or at least i think i would have
the pair that i installed after the first pair were put in definately have the relay coming off the battery. im assuming the first two do also. (havnt traced the wires back but i think they are) the prob only started after i put the second set in so thats whats got me questioning my instalation.
il fiddle with the earth and see how i go.
thanks again

[-Scott-]

Just reading through again, and a silly thought occurred - are you sure it only started when you put the second spotties in? Are you sure it wasn't happening before, and you just never noticed it?

Disconnect your new relay, to confirm the problem goes away.

[ausoops]

thanks, il try the earth. but from memory i think i took the earth from the body of the car or directly off the battery... or at least i think i would have
the pair that i installed after the first pair were put in definately have the relay coming off the battery. im assuming the first two do also. (havnt traced the wires back but i think they are) the prob only started after i put the second set in so thats whats got me questioning my instalation.
il fiddle with the earth and see how i go.
thanks again

are they negatively switched?
the supply may be coming straight off the battery and through the relay, but the relay only has one set of contacts, it doesn't switch both the pos and neg.

[j-top paj]

nah positive swithched.

il try in acouple days when i fill up again as its hard to tell when i get down to under 1/3 on the gauge..
didnt think about removing the relay to test it

[kingchevy]

Nissan's had a slight earthing problem I would be getting a nice body earth going to the battery AND THE CHASSIS they have problems with them.

[TRAKTOR]

I had the same trouble with a set of Hella 4000's. Changed the earth lead, routed it straight to the battery, problem solved.

[Goatse.AJ]

Sounds like a funny earth loop prob....make sure your lights and the guage are earthed properly and it should fix it.

[chimpboy]

Are you sure your power supply is keeping up with the new lamps? If you've hit your alternator's limit you might be dropping from ~13.5V down to 12V or so when you turn the lamps on, which on the fuel gauge would show up as a drop in fuel level.

Just an idea. Earth also sounds like a good thing to check as others have noted.

[the_smoo]

let us know the outcome, cause its an interesting one..

[baddboy]

As mentioned previously. You should definately check to make sure you have a solid earth. You could run a new test earth and see if this fixes the problem. When you say you have 4 lights I would assume they are 100w each. Therefore 400w @ 13.8v = 28.98 amps. That is assuming your car is running and the alternator is at 13.8v. If you were to run these lights with the car of 400w @12.0v = 33.3 amps.
You need to make sure you are running these puppies off a new supply directly from the battery terminal through a fuse of suitable size. Make sure you have some big cable for the feed in, but you can drop the size down to the lights.
I would not be triggering the second relay off the positive feed of one of the existing lights. Not ideal to say the least although will work.
Hope this helps

[Jester]

Hi ya

Just a note on the fuel gauge, I have a 99 GU anmd when I put the spotties on it I had the same problem, pulled over in the middle of the night looking for a fuel leak, and then later discovered it was when I had the spotties on that the gauge moved alo and very quickly, ended up being a bad earth, either through my wire connectors or chassis earth, ended up cleaning the connections, soldering them and running earth to the battery and the problem went away.

Cheers

[j-top paj]

yes it seems to be the earth.
i ran a extra cable to the new lights and it fixed the problem.
all i need to do now is find the time to wire it up nice and tidy.

thanks for the info guys