M38 wiring help

JahRafa · Post by **JahRafa** » Fri Nov 11, 2016 8:27 pm

Are there any circuit breakers/fuse box on the M38 wiring system? I am installing a wire harness but do not want to burn down the vehicle. And I wish not to cut any wires to connect any fuse assemblies unless absolutely necessary.

Post by **wesk** » Fri Nov 11, 2016 11:24 pm

Early M38's had a set of circuit breakers on the inboard side of the cowl battery box:

and one on the back side of the instrument cluster:

The early main light switch did not have a built in CB but the later switches did.

This is the early wiring diagram showing the circuit breakers

This is the late M38 wiring diagram without circuit breakers.

If you are installing a correct M38 reproduction harness you should have been advised by the manufacturer to choose the early or late harness?

JahRafa · Post by **JahRafa** » Sat Nov 12, 2016 7:47 am

Thank you Wes! How can I find out if I have an early or late model M38? Mine is 1952 so I guess that will be late since that was the last year for the M38 model if I am not mistaken. When I purchased the harness I was asked if I had circuit breakers and I chose the ones without, because I did not see any then. But my dad had the vehicle since I was a year old, and there has been many modifications done and it is currently 12 volts. I am trying to bring it back to original 24v. If it is the late model, then are there circuit breakers still or anywhere to put fuses? I appreciate all your help and wisdom

Post by **wesk** » Sat Nov 12, 2016 10:54 am

The group of three Circuit Breakers were last installed in MC 65927.

The instrument cluster circuit breaker was last installed in MC65042

The old style light switch without a circuit breaker was last installed in MC66734.

JahRafa · Post by **JahRafa** » Sat Nov 12, 2016 7:45 pm

Wes. Mine is MC 69612 therefore no circuit breakers. So is it safe to install the harness? or does the light switch has a safety inside? just worried about a short and not having fuses or breakers. Does it have anything for safety feature?

Thanks again.

Rafael

Post by **wesk** » Sat Nov 12, 2016 11:02 pm

Only the late style light switch has a circuit breaker inside of it. For the late M38's that was the only circuit protection in them.

The left and center switches are the early switches and they had no built in circuit breaker. The right switch is representative of all the later switches that came with an internal circuit breaker.

The harness was safe without a lot of circuit breaker or fuse installations as long as it was carefully maintained.

Still it is good insurance to add a battery cut off switch at the negative post of the underhood battery so if a serious short circuit develops you can quickly disable the batteries.

JahRafa · Post by **JahRafa** » Sun Nov 13, 2016 6:05 am

Wes, Thanks again for your wisdom.

Rafael