Dash ground problem

[hdavis]

>
>-- [ From: Eugene Fisher * EMC.Ver #2.5.3 ] --
>
>I had this problem and spent a lot of time trying to fix the dash ground
>. Finally I ran a large wire from the dash ground to "Mother ground"
>the engine .
>
>A symptom of a bad dash ground is that the oil and fuel gauges change
>readings when the lights are turned on. The heavy load causes the
>ground to jump. The new wire went around the problem which is the dash
>connections and fixed the problem.
>
>Chicken I know, but the wires is just too hard to reach behind the dash.

I can tell you about difficult to get to!

I tried the "master dash ground extra wire" trick. No luck. Then on to cleaning all of the dash connections. And resoldering
some of the instrument connections. Still have the gauges jump when the headlights are turned on - but not as much.

Maybe an excuse to buy one of those fancy dash replacements!

Actually, I plan on rerouting the headlamps through relays that are switched by the headlight switch instead of running real
power through the switch.

I'll let you know how it turns out (I'm also considering switching to H4 bulbs ina replacement lamp).

Henry

Henry Davis Consulting, Inc / new product consulting
PO Box 1270 / product readiness reviews
Soquel, Ca 95073 / IP reviews
ph: (408) 462-5199 / full service marketing
fax: (408) 462-5198
http://www.henry-davis.com

 

[hdavis]

>
>-- [ From: Eugene Fisher * EMC.Ver #2.5.3 ] --
>
>Most headlight switches have a safety feature like an auto reset breaker
>so if there is a short your lights will not fail just come on and off. I
>will have to look at the GMC manual to see if this one is the same. I
>guess what I am saying, be sure you are not going to put in some more
>weak link components in the light circuit.
>gene
>

Actually the reason why I'm planning on re-wiring has nothing to do with the intrinsic safety of the existing setup. It's
based on my desire to move from the current sealed beam lights to a replacable bulb H4 type of set up. The current wiring is
inadequate for higher wattage bulbs in my opinion - especially if I add other driving lights.

So my alternatives are to replace the existing switch and wiring, or add a relay controlled circuit for the headlights only.
In the spirit of making as few physical changes as possible in the dash area, I'll use the headlight switch as a control
circuit that carries little current to the relays.

As a side benefit the relay controlled circuit should reduce my grounding problem in the dash. Note: my grounding problem
seems to be a high resistance ground path that I can't find, not an electrical grounding of a live circuit.

The "new" headlight circuit will be less reliable than the existing one because of the two added compoents (relays). The drop
in reliability as measured by MTBF is not a significant issue since it's pretty small. And, in comparison to not being able to
use a newerr headlight system, I'll take the trivial added complexity and associated reduction in reliability.

Henry

Henry Davis Consulting, Inc / new product consulting
PO Box 1270 / product readiness reviews
Soquel, Ca 95073 / IP reviews
ph: (408) 462-5199 / full service marketing
fax: (408) 462-5198
http://www.henry-davis.com

 

[zachary zehnacker]

Henry,

You're right about needing relays to put any more current on the lighting
circuit. We plug our trailer into the GMC for the running lights, tail
lights, and brake lights. We just tied into the original wiring as we had
on several previous tow vehicles. The setup worked fine for several years,
but apparently the connector on the headlight switch eventually corroded,
and the switch melted and just about started a fire. We replaced the
switch and now use a relay to control all the running lights on both the
motorhome and trailer. We still use the headlight switch to flip the relay
and give current to the headlights though. As far as reliability goes, we
use the Potter Brumfield automotive relays quite a bit on our race cars and
have never had a failure. We even used a little relay "logic" for our
cooling system on the race cars. We have also used the Bosch relays with
the good results.

I'm interested in hearing about your results when you switch to the H4
bulbs. We have switched over to the rectangular headlights, and they seem
better than the round ones used to be, but we can always use more and
better focused light. Do you have the round lights or have you also
switched to the rectangular ones?

Zak

>Actually the reason why I'm planning on re-wiring has nothing to do with
the intrinsic safety of the existing setup. It's
>based on my desire to move from the current sealed beam lights to a
replacable bulb H4 type of set up. The current wiring is
>inadequate for higher wattage bulbs in my opinion - especially if I add
other driving lights.
>
>So my alternatives are to replace the existing switch and wiring, or add a
relay controlled circuit for the headlights only.
>In the spirit of making as few physical changes as possible in the dash
area, I'll use the headlight switch as a control
>circuit that carries little current to the relays.

>Henry