Relays and Euro lights

Bernie Benz b.m.benz at
Tue Jun 4 07:27:11 EDT 2002

Welcome back, Scott.  Good to hear from you.

Sounds like you need to use better relays, or move from Chicago.  A 4 pin
relay is not the best choice for this high current, two relay application,
IMO.  Bosch and PB make a 5 pin cube relay specifically for this type app.
in which there is a common input to two sets of 30A NO contacts and dual
outputs, thus dividing the current between two sets of contacts and output
terminals.  This has great wiring advantages in that only one #12 wire need
go into each socket connector.  In your enviroment maybe the relay cover
needs to be replaced with a little silicone caulk.

In my 44s I've had my dual relays mounted on the frame member just behind
the pass headlight, near where the jump post used to be (it's now airborne).
No heat, no corrosion, no fuses, no problems, and wiring runs are as short
as possible.  In the 89 chassis they are mounted on top of the pass strut


> From: QSHIPQ at
> Date: Tue, 4 Jun 2002 08:34:00 EDT
> To: b.m.benz at, brianl at
> Cc: 200q20v at, urq at
> Subject: Re: Relays and Euro lights
> --
> [ Picked text/plain from multipart/alternative ]
> Just read this one....  The case of "new" spec vs element exposed reality.
> The problem with relays is they have a life, specifically, they have a half
> life.  The harsher the environment they operate in, the shorter the half
> life.  In the case of my "underhood" installed relays in my urq for instance,
> the crap wiring job from alt to relays located them right beside the radiator
> (heat and water/salt).  Which reduced the half life of my relays to less than
> two months.  When these pups get hot and/or wet, there is no guarantee of
> spec.  In fact, in my case '83 urq, the relays would randomly arc closed,
> this is *with* a 30 amp inline fuse (then run the battery down).  This
> wouldn't happen if it was sunny, pretty much a guarantee if it was
> raining/snowing (after shut down the lights would either stay on, or the heat
> buildup would turn them on in the middle of the night)
> I put up with this for 4 changes of relays in 6 months, until I recently
> moved and properly mounted them in the glovebox area, and strung 10/12guage
> wire from the battery.  Nary a problem since.  The problem with applying
> 200amps relays is a couple fold.  IF your relays are marginal (not new) you
> DO risk the chance of not only arcing them, but welding them closed AND
> blowing the bulbs out.  I'm only sharing BTDT.  I assure you Bernie, I have
> and understand  the operating specifications of *new* 12v 4pin relays.
> I'm only sharing what I see in practice, and personal experience.  If you
> routinely replace your relays *before* failure, your theory/specification
> applies.  IME, few routinely replace relays before failure.  In the land of
> winter salt, underhood relays fail quite regularly, so do those high amp
> unprotected connections between relay and wiring.  Mounting them near the
> battery post means you put them near the hottest heat generator too (turbo),
> which means half life ain't great.
> "Don't fix if it ain't broke" - ok, but when it does, "Fix it right the first
> time" (?)
> My .02
> Scott Justusson
> practical relay install specialist
> In a message dated 5/31/02 3:20:11 PM Central Daylight Time,
> b.m.benz at writes:
> Do you normally jump start your car with the headlites on?  200 amps will
> flow through a discharged battery with an applied voltage at the jump
> terminal of less than, or very little more than the normal system opperating
> voltage, and rapid chargers are voltage regulated, restricting the peak
> applied voltage to about 15 volts.  They are designed to be idiot proof!
> Further, the arc over voltage of an open relay is well in excess of 600
> volts.
> Bernie
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