johnmeister.com/jeep/sj - Copyright © 1995

Over Voltage Protection Relay

Sun Jul  5, 2009
From: Edward Pomeroy 

John - for your database on the OVP relay and repairing it.


Final report with pictures -  Removed battery, moved first ECU out of the
way. The trick to getting the OVP relay out is that on one side of the
plastic frame that holds it, there is a hole (closed slot) that receives the
tang on one side of the relay box, on the far side closest to the firewall,
it is not a closed but a knife slot.

* **The trick to removing is to carefully twist the relay slightly clockwise
(facing the rear of the can that has the tangs) then pulling/pushing the
relay and blade that goes into the closed pocket outwards (towards the
firewall) at which point the whole relay can be moved away from the plastic
holder and unplugged from the connector. *

Remove the 10A fuse (or two if yours had two), then pry the crimps on the
base of the can away from the plastic pin holder.  It is a very tight fit, I
did minor damage (visible pry marks) on the can.

Picture 25 shows can, relay and minor damage.
Picture 26 show what the relay looks like board side, notice the oxidized
rosin where the factory had re-soldered several point.  Also note the lead
almost in the center that seems to have boulders around the pin, this was
the bad connection, intermittent like all get out. Crystalized tin and
corrosion all round this one point. Of course, this was the one point not
re-soldered at the factory and thus failed. It also happens to be one leg of
the contact feeding the relay contact as best I can determine.
Picture 27 -s looking down from the top, can see the relay coil and big
honking diode.
Picture 28 side view, again looking at relay and large diode in heatsink the
full size of the can wall.
Picture 29 - after cleaning with fine wire brush, re-flowing all the bad and
questionable connections (with high quality 60/40) and then cleaning with
deoxit.

End result!  The ABS light is off, the idle control is back to normal and as
a bonus, now the cruise control which had gone totally random and mostly non
functional, WORKS normally again and I don't get pulsing brakes on the
downhill, which means that if you have pulsing and sometimes self shutoff of
the cruise control on downhill, it is very likely the OVP and not the actual
cruise control amplifier, though I took the latter apart and re-flowed
several questionable connections about a month back, with no change in
behaviour, hence, it was the OVP. This little beastie of a relay seems to
have come into use after 86, the earlier diesels and gassers did not use it
or at least I can't find it in the older manual.

Next, to either pay someone to dismantle the dash and repair/replace the A/C
item leaking in there or to try it myself..... leaning to paying a pro for
that, too much work involved.

Was a great 4th of July, hope everyone  enjoyed the weekend.

Edward