Electrical help needed!

Buzz · #1 (**permalink**) 02-01-2003, 04:32 PM

On our way home last night, my headlights suddenly went out. Lucily we were only a couple of blocks away and on a private road. Hazzards, turn signals and brake lights still worked but headlights, park lights and dash lights were dead. On examination today, I found the fuse on the light switch was burned. I replaced the fuse but I now find that it gets wery hot when the headlights are on and only a bit warm with only the park lights running. Also, another thing I had noticed before is that my fuel gauge is unresponsive when the lights are off but jumps towards the full mark when they are turned on. I have checked and double checked all my light connections as well as the connections to the fuel gauge and sender. Everything is as specified in the manual that came with the (Prodesign) harness. With the fuel gauge and sending unit disconnected, the light switch fuse still heats up with the lights on. I don't know if the two problems are connected but the car has 650 miles on it since I first wired it up and this is the first time that fuse has blown. Help!

RACER X #99 · #2 (**permalink**) 02-01-2003, 04:52 PM

Buzz,
Most auto electrical problems seem to start with bad grounds. With glass cars you have many ground connections. Start checking.

Cranky

computerworks · #3 (**permalink**) 02-01-2003, 05:04 PM

Buzz...
do you have a wiring diagram?
Listening to the fuel gauge "not responding" unless the lights are on...seems to indicate a miswire or an "open" with a 'sneak-path' back to the fuel gauge (maybe a grounding problem at the dash)

I would check the diagram and see if the fuel gauge fits in with the light circuit.... shouldn't.

Fuses are thermal-responding devices, so a high amperage fuse will be warm to the touch when its circuit is carrying current.

Was the fuse the proper rating? If you have the diagram, look and see all the lamps that are powered by this circuit, find the specs on the bulbs and add up their operating current (in Amps).
The total current drawn by the circuits should typically be 75% of the fuse rating... if they all add up to 15 amps, use a 20 Amp fuse.

Is your fuse box in a very hot area? If so, you may have to up the fuse value slightly to "derate", or compensate for the extra heat.

Last observation.. is this lamp circuit also powering the instrument panel lights? .. if so, you may have a wire misplaced on the fuel gauge, such that indicator lamp voltage is powering the meter not the lamp.

Hope some of this helps.

computerworks · #4 (**permalink**) 02-01-2003, 05:05 PM

....if not....use a bigger fuse!

Buzz · #5 (**permalink**) 02-01-2003, 05:06 PM

Thanks, Cranky, will do. Ron, all wiring to the fuel gauge is as specified in the wiring diagram. The only possible connection that I can see is the individual gauge lights which are connected in series. Problem is, even with the fuel gauge light disconnected, the pointer still jumps towards full when the headlight switch is on. It even seems to be semi functional as it indicates closer to full with more fuel in the tank. Am I correct in assuming that the gauge operates on resistance in the ground circuit and therefore indicates a grounding problem? Thanks for the replies.

Buzz · #6 (**permalink**) 02-01-2003, 05:23 PM

To answer the other questions Ron, the fusebox is located behind the dash - not particularly hot. The fuse is a 15amp which came with the switch. I will check the rating of all the lamps on the circuit and upgrade to a 20amp if applicable.

computerworks · #7 (**permalink**) 02-01-2003, 05:24 PM

...the sender in the tank varies the resistance to ground and completes the meter circuit.

Roscoe · #8 (**permalink**) 02-02-2003, 07:24 AM

May sound stupid but do you have a relay on the headlamps?

Roscoe

427 S/O · #9 (**permalink**) 02-02-2003, 07:49 AM

Roscoe is on the mark, relay!!!!!!

Buzz · #10 (**permalink**) 02-02-2003, 12:24 PM

Not a stupid question at all, Roscoe. I'll probably turn out to be the only dummy here. I did some searching through the archives before I hollered for help and I found quite a bit of discussion on relays. Since my harness came with literally everything including the fusebox in a labelled , step by step connection package custom made for a Unique with my engine, I assumed that any necessary relays, fuses, etc would already be there. I looked but cannot find a relay for the headlights.
At Ron and Cranky's advice, I went over every connection and cleaned and reconnected my main ground lug (needed it) along with all other grounds. I did have one mistake in my headlight hi/lo beam connection which I corrected. All dash wiring, gauges, switches, etc is by the book. Damn thing is that while the headlight switch doesn't seem to be getting quite as hot as before, the friggin fuel gauge still moves up towards full when I turn on the lights. If I disconnect the ground at the sending unit it makes no difference. If I disconnect the signal wire, then it remains unresponsive. Any ideas?

Rick Parker · #11 (**permalink**) 02-02-2003, 02:22 PM

Buzz
Is power for the fuel gauge being pulled from the same fuse/circut as the lights? If so check for a short in the wire leading to the fuel sending unit, or disconnect it from circut and check for overheating at fuse. You may also be experiencing voltage fluctuation with lights on that is effecting fuel gauge. Suggest isolating the lighting with a relay on separate circut so amprege for light circut is not directed through switch itself. Electrical gremlins are difficult to isolate. Take it one step at a time. Be sure wire size (gage) is sufficient for load being carried too. 16 is ok for lights from relay to lamps themselves.

.......Rick

wilf leek · #12 (**permalink**) 02-02-2003, 02:31 PM

15A sounds low for a headlamp circuit. Two 60Watt lamps alone draw 10 amps, without the sidelights etc. I would have thought 20A minimum for the fuse.

Headlamps (and other high-current-draw things like radiator fan)should run through a relay so that the switch is only switching the (low) relay coil current. Even so, the feed to the relay (i.e. high power side) should still run through a fuse.

Fuel gauge feed is usually via a voltage stabiliser to elimintae guage fluctuations from varying system voltages.

HTH

computerworks · #13 (**permalink**) 02-02-2003, 02:40 PM

Quote:

Originally posted by wilf leek

to elimintae guage fluctuations from varying system voltages.

Feminine, plural (...or genitive)....no Latin allowed, Wilf

Buzz, the purpose of a relay, in this case is to switch the rather large current 'remotely'..such that a high-amperage line is not run over a long distance and in need of a High-amperage switch.
The dash switch closes the relay with low current to a coil...and the relay contacts close the circuit to the lights.
BUT... the light circuit still runs from a fuse, for protection.

Buzz · #14 (**permalink**) 02-02-2003, 05:27 PM

I appreciate the replies, guys. Sounds like I need to install a relay in the headlight circuit which should be easy enough, but what about the voltage stabiliser? Is that a normal hardware store item that connects in line on the positive feed to the gauge?

wilf leek · #15 (**permalink**) 02-03-2003, 03:37 AM

Buzz - if you take a look through the current forum threads, you will another one entitled "Electrical help needed". In it you will find stuff about voltage stabilisers.

Computerworks - morde mei!

Buzz · #16 (**permalink**) 02-03-2003, 04:00 AM

Thanks Wilf, I'm on it.

Buzz · #17 (**permalink**) 02-03-2003, 06:47 AM

Update. Just to satisfy myself that the problem wasn't in the wiring harness between the dash and the sender, I disconnected the signal and ground wires from the gauge and ran jumper wires directly between gauge and sender. Same symptoms. The only constant is the positive lead to the gauge. All other gauges are fine. I did notice however that the needle also jumps a bit when I turn on the windshield wipers. It still remained unresponsive with the ignition on and lights off. I think I will order a new gauge and sender along with a voltage stabilizer and see what happens.
PS; I drove around quite a bit last night with the lights on and no problems with the fuse - fixing up my grounds seems to have worked, but should I still install a relay?

wilf leek · #18 (**permalink**) 02-03-2003, 03:13 PM

Buzz - try fitting a voltage stabiliser first, it's the cheapest option, and yes, I think you should have a relay to feed the headlamps.

Your gauge is reacting to supply voltage fluctuations caused by various loads coming on and off. The voltage stabiliser will eliminate all of that.

Buzz · #19 (**permalink**) 02-03-2003, 03:45 PM

Sounds good Wilf. The thing that worries me though, is that the system is really nonfunctional in that at no time does it give me an accurate idea of my fuel level. Is it likely that a stable input current could fix that too or do I have two separate problems ie: voltage fluctuations AND a defective gauge and/or sender?
I will install the relay - thanks. Amazing that the "factory" electrical system doesn't include one. I was hoping to get some input over at the Unique owners forum others who are using the same system but no such luck.
On another note, I watch "Top Gear" on the BBC every week where they run various cars on a closed course with the same expert driver to see which car is top dog. From a Pagani Zonda to a Lotus Seven - type replica and everything in between. Really interesting. Why don't some of you UK Cobra guys try to get some snakes on the show to see how they stack up?

fordnut · #20 (**permalink**) 02-03-2003, 08:23 PM

Buzz, I have had a problem much like yours,with the fuel gauge. disconnect the dash light from the gauge. that is the common connection between the lighting system and the gauges. next hook up a temporary ground from the battery direct to the fuel gauge and also to the sending unit. do this before you change componers. alot cheeper. your problem sounds like a ground problem for the gauges and too small of a fuse on the lights you should have a circuit breaker on lights it will self reset when it cools down and allow the lights to come back on. ford cars have a circuit breaker built into the head light switch. (30 amp)