Replacing Relays, What Kind ?

[bigjon42]

A long time motorhomer here, and current executive owner. I need to stock up on Bosch ? relays to replace ones when they go bad. Exactly what do I need ?
Always on ? Normally off ? I looked them up and am confused as to what to get. HELP.

[dons2346]

If they are plug in, remove one and see if it has a diagram on the side/ Take it to a NAPA or CarQuest auto parts store and let them match it up

[bigjon42]

I thought about that, but didn't know if they were all the same. Jon

[twinboat]

The bosch style relays are configured for both NC and NO use. Some have 4 blades and some have 5 blades.

Its the amp rating that's important, that should match.

A 5 blade will work in a 4 blade application, the socket is wired using only 4 blades.

[jacwjames]

Most of the relays on my coach are the same, attached is the parts page with the number on it.



There are a couple of other relays also in front drivers side electrical bay, they are attached to wiring harnesses loose under the black plastic cover.

Hamsar 42-006 is the ALT-Fail relay.
Hella 12193611 is for the fog lights.


Best thing to do is look in all your bays and list anything that may different and take pictures. That's what I've been doing. Comes in handy down the road.

[Wadell]

In the run bay, there is a relay socket that looks like all the other relay sockets that has DRL wires attached to it. That is NOT a relay. It is a logic module that has the same "footprint" as a relay. Plug a 5 blade relay, you wont be able to turn lights off, 4 blade, and you will blow headlight fuses. IF that DRL module fails, best short term solution is unplug it. Many fuses were lost in finding this out, prior to tracing schematic.

[rpasetto]

There are many relays of the 87-87a type. Bosch sold the division which made those relays; sold to Tyco, I believe.

Here's a reference on the connections for the above type of relay: https://www.delcity.net/images/lined...%20Diagram.pdf

[jacwjames]

On Monday I actually had a problem where I couldn't start the rig. It ended up being the rear start switch but when I was going through all the possible problems the number of the relays used is substantial. The best I could do at the time was switch out a couple relays in the starting circuit with one not in the starting circuit.

So I went ahead and ordered 4 new ones to have as spare, cost was ~$27. Cheap insurance.

[Outbound]

While your at Napa I would also order for stock 80 amp continuous duty solenoid/relay, they look like the old ford starter solenoids.